-
Title (dcterms:title)
-
Eng
Northern Red Legged Frog (Rana Aurora Aurora) Terrestrial Habitat Use in the Puget Lowlands of Washington
-
Date (dcterms:date)
-
2004
-
Creator (dcterms:creator)
-
Eng
Schuett-Hames, Joanne P
-
Subject (dcterms:subject)
-
Eng
Environmental Studies
-
extracted text (extracttext:extracted_text)
-
NORTHERN RED-LEGGED FROG (RANA AURORA AURORA)
TERRESTRIAL HABITAT USE IN THE
PUGET LOWLANDS OF WASHINGTON
By
Joanne P. Schuett-Hames
A thesis submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
February 2004
This Thesis for the Master of Environmental Studies Degree
By
Joanne P. Schuett-Hames
has been approved for
The Evergreen State College
By
___________________________
Dave H. Milne, PhD
Member of the Faculty
___________________________
Marc P. Hayes, PhD
Research Scientist
Washington Department of Fish and Wildlife
___________________________
Mary O’Brien, PhD
Conservation Biologist
___________________________
Tim Quinn, PhD
Adjunct Faculty Member
___________________________
Date
ABSTRACT
NORTHERN RED-LEGGED FROG (RANA AURORA AURORA) TERRESTRIAL
HABITAT USE IN THE PUGET LOWLANDS OF WASHINGTON
Joanne P. Schuett-Hames
The Evergreen State College
February 2004
From August 2000 to November 2002, I studied northern red- legged frogs (Rana aurora
aurora) on a 2 ha terrestrial site near Olympia, Washington to better understand their
patterns of terrestrial habitat use. As northern red-legged frogs are thought to be
terrestrial during most of their active season, understanding how they use terrestrial
habitat is crucial to our ability to protect them because terrestrial habitat loss to
development is an increasing pattern in the Puget Lowlands. I used time and areaconstrained searches, telemetry, drift fences with traps, video records, and measurement
of selected environmental and habitat characteristics to obtain demographic and
behavioral data on the terrestrial life history of northern red- legged frogs. In 2001, I
obtained a Schnabel population estimate of 60 frogs (95% CI +/- 81) for the study site;
alternative methods indicated that a minimum of 54, up to a maximum of 78 northern
red-legged frogs used the study area. Demographic data revealed that post- metamorphic
frogs ranging in size from small juveniles to large adults (36-79 mm snout-vent length)
occupied the site from April to November. Individual frogs had an active-season home
range that included forest, forest-edge, a forest opening with a yard and garden, and tidal
mudflat margins. Some frogs returned to the same home range annually. Spring to midfall growth was greater than annual growth (p = 0.0023) suggesting terrestrial conditions
may be important for feeding. Video analysis revealed that diurnally, frogs were highly
conservative in their movements; movements were brief and rapid and frogs remained
motionless 99.5% of the time. A preliminary ethology of the northern red- legged frog in
its terrestrial environment is presented. Behavior categories include postural, distance
and in-place movements, movement patterns and home ranges, physiology,
predator/danger responses, habitat modification, vocalization and social structure. I also
present a preliminary model to explain the behavior of terrestrial northern red-legged
frogs in response to seasonal changes. In spring, moisture and temperatures do not
appear to limit habitats available to frogs for feeding and other needs. By mid-summer,
dry and warm conditions restrict moist temperature-attenuated habitats and frog behavior
patterns shift in ways that appear to be strategies for obtaining moisture and preventing
desiccation. Late fall to early winter cool temperatures limit frog activity. Overall, frogs
alter their behavior and habitat utilization patterns in differing ways that may allow them
to maintain terrestrial activity such as feeding from spring through early winter (including
during overwintering). Significant conservation implications of this study were: (1) in
terrestrial locations similar to the study area, forest habitat appears to be a requirement
for northern red- legged frogs during both active and overwintering seasons, and (2)
migration routes that cross roads may present a substantial risk. Based on interviews
with amphibian biologists, I outlined a system for achieving the long-term maintenance
of robust populations of this species in Washington.
TABLE OF CONTENTS
LIST OF FIGURES .............................................................................................................v
LIST OF TABLES ..............................................................................................................vi
ACKNOWLEDGEMENTS .............................................................................................. vii
CHAPTER 1. INTRODUCTION ...................................................................................... 1
Need/Rationale and Conservation Overview .................................................................. 1
Geographic Range and Life History Overview............................................................... 6
Terrestrial Habitat Use Overview ................................................................................... 7
CHAPTER 2. METHODS ............................................................................................... 13
Site Description............................................................................................................. 13
Demographics ............................................................................................................... 14
Environmental Conditions ............................................................................................ 19
Terrestrial Natural History and Behavior...................................................................... 21
Data Analysis ................................................................................................................ 23
CHAPTER 3. DEMOGRAPHIC RESULTS ................................................................... 26
Population Numbers (Year 2001) ................................................................................. 26
Size, Gender, and Age ................................................................................................... 30
Deformity and Mortality Characteristics ...................................................................... 35
CHAPTER 4. ENVIRONMENTAL CONDITION RESULTS ...................................... 36
Study Site Temperature and Moisture Conditions ........................................................ 36
Tidal Channel Salinity .................................................................................................. 40
CHAPTER 5. NATURAL HISTORY AND BEHAVIOR RESULTS ........................... 43
Telemetry...................................................................................................................... 43
Temporal Extent of Terrestrial Use .............................................................................. 44
Migratory Patterns and Migratory Stop-Overs ............................................................. 45
Home Ranges ................................................................................................................ 47
Northern Red-legged Frog Ethology and Natural History in Terrestrial Habitat ......... 51
Behavior Patterns in Response to Seasonal Environmental Variables of Temperature
and Moisture ................................................................................................................. 60
Summary of Terrestrial Behavior ................................................................................. 65
CHAPTER 6. DEMOGRAPHIC, ENVIRONMENTAL CONDITIONS, AND
NATURAL HISTORY AND BEHAVIOR DISCUSSION ............................................. 68
Demographics ............................................................................................................... 68
Analysis of Hypothesis Regarding Attraction to Human-Created Openings ............... 70
Synthesis of Moisture and Temperature Data and Behaviors....................................... 71
CHAPTER 7. SPECIES CONSERVATION................................................................... 77
Introduction................................................................................................................... 77
Results and Discussion ................................................................................................. 78
This Study’s Contribution to Conservation of the Northern Red- Legged Frog, and
Recommendations for Further Study............................................................................ 80
CHAPTER 8. KEY FINDINGS ...................................................................................... 81
Demographics ............................................................................................................... 81
Behavior........................................................................................................................ 81
Conservation ................................................................................................................. 82
LITERATURE CITED ..................................................................................................... 84
iii
APPENDIX A. Year 2001 survey type and number of frogs. ......................................... 89
APPENDIX B. Area-constrained survey data. ................................................................ 90
APPENDIX C. Schnabel population estimate. ................................................................ 91
APPENDIX D. Frog size, gender and age. ...................................................................... 92
APPENDIX E. Growth data. ........................................................................................... 93
APPENDIX F. Study site temperature and moisture conditions. .................................... 97
APPENDIX G. Telemetry results. ................................................................................... 98
APPENDIX H. Behavior descriptions. .......................................................................... 104
APPENDIX I. Conservation Surveys. ........................................................................... 109
iv
LIST OF FIGURES
Figure 1. Map of Washington State showing the range of the northern red- legged
frog, the Puget Lowland Ecoregion, and the study site ......................................1
Figure 2. The study area location and the road mortality survey route ...........................13
Figure 3. Locations of drift fence/trap arrays and thermographs .....................................16
Figure 4. Frequency distribution: number of frogs found during 2001 areaconstrained searches..........................................................................................27
Figure 5. Frequency of tagged frog capture through all survey types, during 2001 ........28
Figure 6. Comparison between area-constrained data expanded to the full study area
and the Schnabel population estimate...............................................................30
Figure 7. Red-legged frog snout-vent length measurements by gender ..........................31
Figure 8. Red-legged frog weights by gender May 2001 through October 2002 ........... 33
Figure 9. Red-legged frog snout-vent length and mass ...................................................34
Figure 10. Seasonal moisture and temperature regime at the study site in 2001 ..............36
Figure 11. Precipitation, and air and ground temperatures ...............................................37
Figure 12. Bi- weekly mean moisture conditions in the study area open and forest
habitat..............................................................................................................38
Figure 13. Mean daily temperatures at core sites showing reversal of air versus ground
temperatures.....................................................................................................41
Figure 14. Salinity in the tidal channel and in sand bar or mudflat substrate ...................42
Figure 15. Telemetered frogs home ranges and migratory patterns in 2001 ....................43
Figure 16. Telemetered frog 501C400240 map of 2001 mid- fall cold weather
migratory stop-over, mid-fall possible migratory route, and mid-fall
through early winter home range ................................................................... 48
Figure 17. Cold-weather migratory stop-over temperature and rainfall conditions .........48
Figure 18. Spring through summer home range and macro-habitat use by female
telemetered frog 424E61451B ........................................................................49
Figure 19. Locations of three frogs found during summer of 2002, that were previously
found in 2000 and/or 2001 ..............................................................................51
Figure 20. Movement rate for frog 501C750D68 .............................................................58
Figure 21. Proportion of each type of behavior in 122 total seconds of movement
for frog 501C750D68 ......................................................................................58
Figure 22. Case study for frog 501C750D68 ....................................................................59
Figure 23. Frog 5028025B2D visibly moist while in a deep crouch position on
moist soil on a hot summer day.......................................................................61
Figure 24. Mid- fall structural locations within a sword fern and maple leaf complex
that were used at differing temperatures by female frog 501C400240 ...........64
Figure 25. Frog visibility, structural location, and temperature .......................................65
Figure 26. Seasonal frog use of the study area in 2001 ....................................................66
Figure 27. Model showing observed responses to moisture and temperature gradients ..73
v
LIST OF TABLES
Table 1. Washington and Puget Lowland Ecoregion amphibian conservation status .......3
Table 2. Thermograph and statio n characteristics ...........................................................20
Table 3. Time-constrained and area-constrained search catch per hour ......................... 27
Table 4. Drift fence catch per trap day.............................................................................27
Table 5. Schnabel population estimates ...........................................................................29
Table 6. Population comparison ......................................................................................29
Table 7. Ratio of newly tagged versus total number of frogs caught seasonally.............30
Table 8. Core and supplemental station temperatures .....................................................40
Table 9. Distances moved by frogs within their home ranges .........................................50
Table 10. Preliminary northern red-legged frog ethology and natural history in its
terrestrial habitat ...............................................................................................52
Table 11. Red- legged frog video analysis overview.........................................................53
Table 12. Video analysis of number of frog movement behaviors and seconds of movement activity......................................................................................................54
Table 13. Area-constrained survey number of frog observations and 3-day antecedent
rainfall, early summer through early fall...........................................................62
Table 14. Components of a system to achieve the goal: “To maintain robust populations of northern red-legged frogs throughout their historical range within
Washington State.”.............................................................................................79
Table A-1. Frog survey data .............................................................................................89
Table B-1. Area-constrained survey catch totals ..............................................................90
Table C-1. Tag status of area-constrained search day frog captures ................................91
Table D-1. Frog measurements .........................................................................................92
Table E-1. One year snout- vent length growth, by gender, for six frogs .........................93
Table E-2. Within-year snout-vent length growth, by gender, for 12 frogs .....................94
Table E-3. One year mass growth, by gender, for three frogs ..........................................95
Table E-4. Within-year mass growth, by gender, for 12 frogs .........................................96
Table F-1. Seasonal temperature and moisture regimes at the study site .........................97
Table G-1. Overview of telemetry results for 10 female red-legged frogs.......................99
vi
ACKNOWLEDGEMENTS
I thank my advisor Dave Milne, readers Marc Hayes, Mary O’Brien and Tim Quinn,
and MES Program Director John Perkins. I appreciate your extensive support,
recommendations, creative thinking, and dedication to healthy ecosystems.
I am very grateful to Dave Schuett-Hames for assistance with making and installing
traps, field set- up, assisting with frog capture and photography; Carolyn Comeau and
Tiffany Hicks for trap construction; and Nobi Suzuki, Kelly McAllister and Bill Leonard
for helpful discussions.
Thank you to Marc Hayes, Klaus Richter, Kelly McAllister, J. Tuesday Shean, and,
Mike Adams for participating in conservation surveys.
Winter telemetry data collection represented a cooperative project with Marc Hayes,
Tiffany Hicks, Merrie Diehl and Rob Price of Washington Department of Fish and
Wildlife. In addition, I appreciated access to the land of neighbors near the study site to
search for telemetered frogs, and study assistance and access to the frogs’ winter home
ranges by Liz, Sam, McKenzie and Cooper Devlin.
I dedicate this thesis to my family.
vii
viii
CHAPTER 1. INTRODUCTION
Need/Rationale and Conservation Overview
Between 2000 and 2020, the human population of counties within the Puget Sound
region of Washington State is expected to grow by two million, an overall increase of
29% (Washington Office of Financial Management 2002). This growth will convert
undeveloped habitat to landscapes with substantial area that is hostile to northern redlegged frogs (Rana aurora aurora), e.g., roads, parking lots and other impervious
surfaces and human structures. As roughly half of northern red- legged frog range within
Washington lies within the Puget Lowland Ecoregion (Omernik 1987; Fig. 1)1 , this
species will be vulnerable to habitat modification through a large portion of its range.
Puget Lowland Ecoregion
Study Site
Figure 1. Map of Washington State showing the range of the northern red-legged frog,
the Puget Lowland Ecoregion, and the study site. Base map from Dvornich et al. (1997).
Ecoregion boundary from Omernik (1987).
In the late 1980s, scientists became aware that amphibian population declines were a
global phenomenon. By the early 1990s, documented declines and extinctions focused
1
I am using data for the Puget Sound region as a rough approximation of the expected trend for the
ecoregion. Readers are referred to Washington Office of Financial Management (2002) for additional
specifics.
1
further attention on this issue (Tuxill 1998). Amphibians with permeable skins and
unshelled eggs are especially susceptible to environmental insult such as chemical
pollutants and increased ultraviolet light. Moreover, their use of both aquatic and
terrestrial habitat presents opportunity for a greater range of environmental conditions to
adversely affect species survival (Mattoon 2000). Habitat loss, pollution, climatic
instability, increased ultraviolet light, disease, and introduced predators are among factors
that have been identified in association with amphibian species decline in case studies
(Mattoon 2000; Tuxill 1998). Synergisms among factors are also suspected, e.g.,
climatic change may stress amphibian immune system function, allowing ordinarily
benign fungi or bacteria to become virulent pathogens (Mattoon 2000; Tuxill 1998).
In a recent status survey of about one-eighth of the world’s amphibian species, 25%
were judged to be endangered or vulnerable, and 5% more were nearing threatened status
(Tuxill 1998). Amphibian data for Washington State and the Puget Lowland Ecoregion
(hereafter Puget Lowlands) (Table 1) also indicate high levels of decline or concern. Of
25 amphibian species indigenous to Washington, 36% have a state conservation
designation of endangered (8%), sensitive (4%), or special concern (24%). None of
Washington’s amphibians are federally listed as threatened or endangered, however, 36%
have federal candidate or species of concern status.
Sixteen native amphibian species occupy the Puget Lowlands. Of these, 19% have
state conservation designations and 31% have federal designations. Based on state
classification, 28% of anurans (frogs) in the Puget Lowlands have a specific conservation
status, and at the federal level, 57% have a conservation status (Table 1), indicating
conservation concern for Puget Lowland anurans. One species, the western toad (Bufo
borealis) has incurred a large decline in the Puget Lowlands since the mid-1990s (Adams
et al. 1999, McAllister, pers. comm. 2002). Why this ecoregion-wide decline has
occurred is unknown (McAllister, pers. comm. 2002).
The northern red-legged frog has no state conservation classification in Washington,
but it is included as a federal species of concern (Washington Department of Wildlife
2002). It is however, classed as a sensitive species in both Oregon (Oregon Department
2
Table 1. Washington and Puget Lowland Ecoregion amphibian conservation status (sources:
Washington Department of Fish and Wildlife 2002; Leonard et al. 1993; Dvornich et al. 1997).
Washington State Indigenous Amphibia
Amphibia
Total No. Species
State
Endangered
Threatened
Sensitive
Candidate
Total:
b
Addt. Monitor
Federal c
Endangered
Threatened
Candidate
Concern
Total:
Caudata
(salamanders)
No.
%
a
Anura
(frogs, toads)
No.
%
No.
%
25
100
14
100
11
2
0
1
6
9
7
8
0
4
24
36
28
0
0
1
4
5
3
0
0
7
29
36
21
0
0
1
8
9
0
0
4
32
36
0
0
0
3
3
0
0
0
21
21
Puget Lowland Indigenous Amphibia
Amphibia
Caudata
(salamanders)
No.
%
a
Anura
(frogs, toads)
No.
%
No.
%
100
16
100
9
100
7
100
2
0
0
2
4
4
18
0
0
18
36
36
1
0
0
2
3
3
6
0
0
13
19
19
0
0
0
1
1
2
0
0
0
11
11
22
1
0
0
1
2
1
14
0
0
14
29
14
0
0
1
5
6
0
0
9
45
55
0
0
1
4
5
0
0
6
25
31
0
0
0
1
1
0
0
0
11
11
0
0
1
3
4
0
0
14
43
57
a
There are two established introduced frogs: the bullfrog (Rana catesbeiana ), and green frog (R. clamitans). They are not included
in this chart.
b
For Washington State, all state E,T,S and C species are also priority species and monitor species. Species without E,T,S or C
status may be categorized as monitor. This line lists the number of additional monitor species.
c
All species with federal designations additionally have state designations, except the red-legged frog. This species is a federal
species of concern, but has no state designation.
of Wildlife 1997) 1 and British Columbia (COSEWIC 2002) 2 .
A separate sub-species of red-legged frog found in California, the California redlegged frog (R. aurora draytonii) was listed under the Federal Endangered Species Act in
1996. This sub-species has incurred a 70% reduction in range, and in its southern
California range extent, only one of 80 previously known sites is currently known to have
this species extant. Decline of this sub-species is attributed to habitat loss and alteration,
over-exploitation for food in the late 1800s and early 1900s, and impacts from exotic
predators (U.S. Fish and Wildlife Service 2000).
1
This designation is given to Oregon species that may become threatened or endangered, to assure
protective measures are put in place (Oregon Department of Wildlife 1997). The Willamette Valley
populations have a sub-class of vulnerable “Species for which listing as threatened or endangered is not
believed to be imminent and can be avoided through continued or expanded use of adequate protective
measures and monitoring.” The Oregon Coast Range, West Cascades, and Klamath Mountain populations
are sub-classified as undetermined status “Species for which status is unclear. They may be susceptible to
population decline of sufficient magnitude that they could quality for endangered, threatened, critical or
vulnerable status but scientific study would be needed before a judgment can be made.”
2
The status in British Columbia is a federal status “special concern” due to “…characteristics that make it
particularly sensitive to human activities or natural events.”
3
Although there is no definitive data on population decline for the northern red- legged
frog for the Puget Lowlands, there are indications that decline may occur in this
ecoregion under development and urbanization scenarios. For example, McAllister (pers.
comm. 2002) has observed that the northern red- legged frog is absent from highly
urbanized areas, e.g., downtown Seattle, or downtown Olympia. Additionally, in rapidly
developing areas within King County, Washington, Richter and Ostergaard (1999)
recorded red- legged frogs at 25% fewer wetland sites in 1997 than when they initiated
surveys in 1993.
Development almost invariably changes watershed hydrology, and stormwater ponds
represent one remediation strategy often implemented to attempt to ameliorate such
changes. Ostergaard (2001) studied amphibian use of 52 stormwater ponds in
developments within King County. Overall, she found “…some stormwater ponds may
function as biological traps for native amphibians, and some may function as sources.”
Red- legged frogs were found in 50% (26) of the ponds. Her results indicated that
landscape condition (percent total impervious surface condition within a 1,000- m radius
of a stormwater pond) was the most important of 29 factors measured in explaining
northern red-legged frog abundance. Northern red- legged frog abundance was also
negatively correlated with maximum water level fluctuation, and egg mass numbers were
greater at sites that had not been cleaned out within the last 1.5 years.
Direct sources of mortality observed by Ostergaard (2001) were: (1) egg mass
stranding due to rapid water level drops, especially in newer ponds with steep banks; and
(2) children “…collecting amphibian eggs and larvae to throw, play with, and take home
to raise.” Exotic fish that are potential predators of amphibians (koi, Cyprinus carpio;
goldfish, Carassius auratus; and blue gill, Lepomis macrochirus), were also found in
three stormwater ponds. Bullfrogs were present in 44 of the 97 pond bays and were most
abundant in permanent ponds. Ostergaard (2001) did not find a bullfrog effect on native
species richness, and bullfrogs were not important in logistic regression models
predicting the occurrence of native amphibian eggs and larvae. However, it is unknown
as to whether unstudied effects from bullfrogs might be occurring.
Another aspect of habitat loss is the disproportionate loss of small wetlands and
shallow portions of larger wetlands (reviewed by Adams 2000). Adams (1999) found
4
survival of larval red- legged frogs to be generally lower in permanent ponds, and he
pointed out that maintaining a diverse mix of wetland types, (including ephemeral
wetlands), may help promote native amphibian conservation.
Roads can be a substantial source of mortality for amphibians due to the fact that road
locations cross landscapes that frogs use seasonally. For example, in a study in southern
New York that included telemetry of green frogs (R. clamitans) en-route to overwintering
habitat, three of four frogs that crossed a busy road were killed by automobile traffic.
The frog that survived likely did so due to crossing at 0200 hr (Lamoureux & Madison
1999), presumably during an interval when traffic levels were low.
Citing study results for the green frog that indicate adult overwintering habitat might
be as important for sustaining populations as is breeding habitat, Lamoureux and
Madison (1999) have highlighted the importance of examining “amphibian habitat
requirements at all times of the year, not just during the breeding season.” Until recently,
northern red-legged frogs were largely unstudied during their active season, which has
been shown to be largely terrestrial (Ritson & Hayes 2000; Haggard 2000). Paucity of
research has hindered understanding the importance of northern red- legged frog
terrestrial habitat.
My study was intended to help develop better understanding of how northern redlegged frogs use terrestrial habitat (including that modified for residential use). I focused
on gathering demographic and behavioral data on a 2- ha site of largely mature forest but
which contained an opening with a home, yard and gardens. My study site was located in
the southern portion of the Puget Lowlands, near Olympia, Washington (Fig. 1).
The primary research question that I attempted to address was:
“Do northern red-legged frogs show a preference for a human-created forest opening
with grasses, forbs, and gardens over adjacent undeveloped forest?”
I additionally investigated demographic and natural history questions in support of
the primary research question, and to add to knowledge of how red-legged frogs use
terrestrial habitat. These were:
1) Population demographics
a) How many frogs use the study site?
b) What are size, gender, age and mortality characteristics of the frogs?
5
2) Temporal use of upland habitat and movement patterns
a) When do frogs use the study site?
b) What movement patterns do frogs engage in?
3) What are the temporal, spatial and habitat characteristics of frog home ranges?
4) What are observable frog behaviors and activity patterns?
I also performed a series of conservation interviews/surveys with amphibian
biologists to clarify conservation issues and status for this species in the Puget Lowlands,
and western Washington.
The primary field research period was April through December 2001.
Reconnaissance field research occurred August and September of 2000, and
supplementary data were collected from April through November of 2002. Conservation
interviews were accomplished July 2002.
Geographic Range and Life History Overview
Geographic Range
Northern red- legged frogs range from southwestern British Columbia through
western Washington (and in the Columbia River Gorge east to White Salmon), western
Oregon, and into northwestern California (as summarized by Leonard et al. 1993;
Nussbaum et al. 1983; and Dumas 1966). They occur from sea level to 860 m in
Washington, and up to 1427 m in Oregon (Leonard et al. 1993).
This species is relatively widespread and appears to be generally common over most
of its range in Washington. Although broad-scale geographic studies are lacking, studies
at scattered locations in the Puget Lowlands have revealed occupancy patterns of
50%
of study sites. Adams et al. (1998) found red- legged frogs at 58% (23 of 40) of lentic
study sites within Fort Lewis. Similarly, Adams et al. (1999) found this species at 58%
(14 of 24) of lentic study sites on Navy lands in the Kitsap and Toandos Peninsulas.
Ostergaard (2001) observed red- legged frogs at 50% (26 of 52) of surveyed stormwater
ponds in King County.
Life History
Breeding, hatching and metamorphosis-- Northern red- legged frogs breed from
January to March in western Oregon and Washington (Dumas 1966), and from February
6
to March in British Columbia (Licht 1974). Specifically, Adams (1999) reported redlegged frogs breed at Fort Lewis in Washington in early March. Storm (1960) reported
that in the Corvallis, Oregon, area, they breed in January and February, hatch in 6 to 7
weeks, and metamorphose in June and July. Licht (1974) reported metamorphosis in July
for British Columbia. Adams (1999) found the beginning of metamorphosis in late July
for Fort Lewis frogs. Brown (1975) reported late July for metamorphosis at a breeding
area near Bellingham, Washington, whereas Ostergaard (2001) found metamorphosis as
early as May in shallow, warm stormwater ponds in King County.
Northern red- legged frogs are thought to reach sexual maturity at 2 years at a size of
ca. 50 mm snout-vent length (SVL) for males and ca. 60 mm for females (Storm 1960).
In contrast, male frogs near Olympia developed nuptial pads during late summer their
first year (Hayes & Hayes 2003) and began to call (Hayes et al. 2004). Females are
thought to breed every year (Licht 1974).
Whether northern red- legged frogs have a meta-population structure is unknown
(Hayes, pers. comm. 2003).
Size-- Recently metamorphosed juveniles near Corvallis were 20 to 25 mm SVL
(Storm 1960), and near Bellingham 26 to 30 mm (Brown 1975). The maximum SVL for
adult red- legged frogs near Corvallis was 68 mm for males, and 100 mm for females
(Storm 1960). The size range of nine breeding females from the Corvallis area was 72 to
93 mm SVL (mean 84 mm), and for 11 breeding males was 49 to 65 mm (mean 59 mm).
According to Nussbaum et al. (1983) males are < 70 mm.
Survival rates-- Licht (1974) found mean survival of eggs to hatching of 91 to 92%,
but from hatching to metamorphosis of < 1%. After one year, there was a minimum of
52% survival of those frogs that had metamorphosed the prior year. Licht (1974) also
reported a yearly minimum survival rate for frogs > 1 year old, of 69%.
Terrestrial Habitat Use Overview
Terrestrial Habitat Characteristics
In northern California, Haggard (2000) found 52% of telemetered northern red-legged
frog observations were in closed canopy thicket/forest macrohabitat. An additional 19%
of sightings were in forbs, 17% in emergent (wetland) vegetation, 8% in grassland, and
7
4% under human-created habitat such as under boards. Although not assessed, Haggard
(2000) mentioned sword ferns might be an important microhabitat for the frogs.
Home Range Size
In northern California, Haggard (2000) identified a mean range length (the distance
between the expected breeding location and the furthest location that the frog was found)
for northern red- legged frogs of 73 m (s = 67.2 m, range: 5 to 221 m).
Seasonal Movement
Collectively, observations indicate that northern red-legged frogs engage in
movements during three discreet periods: pre-overwintering (fall), breeding (winter), and
post-breeding (spring). In the South Umpqua basin of Oregon, Hayes et al. (2001) found
that northern red-legged frogs can travel long distances after they exit the breeding pond
seasonally. They reported adults up to 2.4 km from the breeding pond where they had
been originally captured, and more recent data has found frogs up to 4.8 km from the
breeding pond (Hayes, pers. comm. 2004). At this site, seasonal movement upwards of
1.0 km from the breeding pond appear to be routine (Hayes, pers. comm. 2004).
Conversely, Haagard (2000) reported the furthest distance northern red- legged frogs
moved from a northern California (expected) breeding area was ca. 20 to 280 m (mean =
149, s = 83.6).
When temperatures dropped in the fall, Ritson and Hayes (2000) found that three
female telemetered frogs each made a pre-overwintering move of over 40 m from
terrestrial habitat to water at a lower Columbia River site in Oregon (Ritson and Hayes
2000).
In studies conducted near Corvallis, Oregon from 1950 to 1953, Storm (1960) found
that male frogs arrived at breeding ponds first (as early as 8 December). No females
were seen until at least 11 January. Females appeared to move to the breeding pond after
1 January when air temperatures were 10 C (50 F) or above during at least moderate
rains. Licht (1969) reported northern red-legged frogs in southwestern British Columbia
emerged from hibernation in February and March, and moved to breeding sites when the
air was a minimum of 5 to 6 C.
8
In a Thurston County, Washington telemetry study completed in 2001, Shean (2002)
found post-breeding female red- legged frogs remained at the breeding pond until midApril. At this time, coincident with warmer air and water temperatures, females moved
to other wetlands or in one case, uplands until 25 May 2001, when the study concluded.
Local Movement and Daily Activity Patterns
Haggard (2000) studied the movement ecology of 11 female and one male northern
red-legged frogs at Freshwater Lagoon, Humboldt County, California. Through the use
of telemetry, she determined for the March to July 1999 period of study, that most of the
frogs (11 of 12) stayed on land 90% of the time, and although daily moves of up to 87.5
m were made, most moves were
5 m (mean = 3.7 m, s = 5.1 m). She found no seasonal
or daily weather response pattern, and no synchronous pattern of movement between
study frogs for movements
20 m. Overall, the frogs “tended to stay
5 m from water.”
Storm (1960) describes northern red- legged frog terrestrial use as follows: “Frogs
often forage in damp well-shaded areas during the day and are active during warm rains
at night.” Chan-McLeod (2003) studied northern red-legged frogs May through October
in terrestrial plots. She found they were often not visible, and were “burrowed into
coarse wood, ground vegetation, loose ground substrate, or cavities.”
Chan-McLeod (2003) found northern red- legged frogs primarily utilized forest rather
than clearcut habitat. When movement into a clearcut occurred, it was more likely to be
by a frog with a larger mass, and to be positively related to rainfall.
Overwintering Behavior
Ritson and Hayes (2000) found three adult female northern red- legged frogs along the
lower Columbia River in Oregon, overwintered and remained in water when it was cold,
but emerged onto land during warmer winter intervals. Licht (1969), reporting
overwintering in southern British Columbia in “both river and woods” may have found a
similar pattern, but his study was not focused on overwintering.
Diet and Feeding
Nussbaum et al. (1983) summarized the scant literature, largely based on Fitch (1936)
on diet items of northern red-legged frogs. The frogs eat beetles, caterpillars, isopods,
and other small invertebrates. They may occasionally eat vertebrates that are small
9
enough; Rabinowe et al. (2002) reported ingestion of a 45- mm Columbia torrent
salamander, Rhyacotriton kezeri, that was subsequently rejected.
Licht (1974) found in a sample of 104 collected northern red-legged frogs, that all had
food in their stomachs. He also tested starvation tolerance for 20 newly metamorphosed
northern red-legged frogs and found that 50% died at a mean age of 32 days.
Moisture Requirements and Adaptations
Rates of hydration and dehydration-- Dumas (1966), studying Pacific Northwest
Ranidae, separated them into “pond frogs” (R. pretiosa, R. luteiventris and R. cascadae)
and “wood frogs” (R. aurora and R. sylvatica) based on their natural history. In
particular, he described pond frogs as rarely “found more than a few yards from water.”
In contrast, wood frogs “are not as closely confined to the immediate vicinity of water as
are the pond frogs. Adult aurora are commonly found among rank, damp herbaceous
vegetation or among tangled complexes of logs as much as 1,000 yards [ca. 920 m] from
the nearest [fresh] water.”
To support his categorizations, Dumas (1966) performed tests among the five species
to determine whether differences existed in rates of dehydration and rehydration. For all
taxa, the rate of water loss was greatest in the first hour and the most rapid rehydration
rate occurred in the second ½ hr. Dumas (1966) found that wood frogs lost and gained
water more rapidly than pond frogs. He surmised that it could be ecologically useful for
a wandering terrestrial frog to rapidly gain moisture if it was approaching a lethal
desiccation level.
Hydrotaxis-- To further test the difference between wood and pond frog groups,
Dumas (1966) placed five each of aurora, cascadae and pretiosa within an enclosure
13.4 m (44 ft) from a shallow pan of water. By 42 min, all of the cascadae and pretiosa
found the water, but it took 87 min for all the aurora to find the water. This suggests
water is important to all the taxa studied, however getting to water fast may have been
less important to aurora, possibly due to a greater tolerance to dehydration (e.g., see
Shoemaker et al. 1992).
Behavior during drought-- The Pacific Northwest has a temperate, maritime, wet
climate. However, Norse (1990) describes another aspect, summer drought: “Although
renowned for wetness, it experiences summer drought unknown in moist regions of east
10
Asia, eastern North America, or western Europe.” Chan-McLeod (2003) identified that
extreme high temperatures decreased the likelihood that northern red- legged frogs would
enter a clearcut as compared to an old growth forest. However, behaviors used to survive
drought have not been described.
Temperature Requirements and Adaptations
Preferred body temperature -- In studies of preferred temperatures, Brattstrom
(1963) reported a body temperature mean of 13.3 C (range: 9.8 – 19.0 C, n = 13) for R.
aurora1 , which was the lowest mean of the 12 Rana species studied. The mean for the
Ranidae was 21.6 C.
Mechanisms of heat gain and loss-- Brattstrom (1963) reported that R. aurora uses
solar radiation (e.g., basking) to raise its body temperature. However he noted “…the
species usually remains in cool, moist places apparently so that the body temperature will
not reach high levels.” Brattstrom (1963) found that the primary ways amphibians gain
heat are basking in sun, conduction from substrate and water, and convection from air.
Heat loss occurs through conduction and radiation to the substrate (water and air),
convection to air, and evaporative cooling. These mechanisms allow amphibians to be at
somewhat different temperatures from those of the surrounding environment.
Critical thermal maximum and minimum-- These data are lacking for northern
red-legged frogs. Brattstrom (1968) presents data from amphibian tests of the critical
thermal maximum and minimum (the high and low temperatures where an amphibian
turns onto its back, and is unable to escape from conditions that result in death). Of
these, information for R. cascadae, pretiosa, boylei and sylvatica from British Columbia
and California are likely the most relevant to R. aurora. Critical thermal maxima for
these species were between 30.3 and 34.8 C. The critical thermal minimum (R. cascadae
and pretiosa only) was –1.0 C. Brattstrom and Lawrence (1962) found that acclimation
to lower or higher temperatures for 1 to 3 days lowered or raised (respectively) the
critical temperature for amphibians. Specifically, the critical thermal minimum for R.
pipiens decreased by 3.3 C, and the critical maximum increased for R. palustris by 1.7 C
and R. clamitans by 5.1 C.
1
This study does not specify subspecies or location making it possible that the California red-legged frog
(R. aurora draytoni) was either the focus of or was included in these results.
11
Response to Active Season Habitat Loss
No studies directly addressing effects of active season habitat loss on northern redlegged frogs exist. However, the results of one study (Chan-McLeod 2003) indicate that
clearcutting forest habitat sharply reduces northern red- legged frog active season use of
that habitat. Chan-McLeod (2003) found 86% of frogs during 120 trials, each averaging
22 days, used old-growth forest habitat nearly exclusively as compared recent clearcut
habitat. Those frogs that primarily used the old growth forest but also used the clearcut
only moved short distances into the clearcut and only for short (unspecified) lengths of
time.
The remaining 14% of the frogs stayed in the clearcut for several days, or moved
through it (Chan-McLeod 2003). A higher proportion of frogs (28/40) ventured into a
clearcut with a young stand of trees < 4 m high, than into clearcuts with sparse newly
planted young trees (3/40 and 5/40). In addition, frogs that moved into the clearcut
stayed close to the forest edge (12.7 m) whereas those in the forest stayed 44.3 m from
the edge.
Causes of Mortality to Terrestrial Red-Legged Frogs
Predators of the red- legged frogs during terrestrial habitat use include the common
garter snake (Thamnophis sirtalis pickeringii) (Gregory 1978, 1979; Shean 2002), mink,
otter, and potentially raccoons (Appendix I). Human caused (or related) terrestrial
mortality factors include vehicle traffic (Beasley 2002). Although skin toxins of northern
red-legged frogs are generally thought to be effective in preventing predation by domestic
cats (Hayes, pers. comm. 2002) domestic cats have been observed to catch and play with
this species, which can lead to mortality (Milne, pers. comm. 2002).
12
CHAPTER 2. METHODS
Site Description
The 1.95-ha study area (Fig. 2) is in the Puget Lowland Ecoregion (Omernik 1987),
within Thurston County, Washington. The climate is temperate, with cool wet winters,
and warm dry summers. Annual precipitation in this ecoregion is 88 to 125 cm (Omernik
and Gallant 1986). Approximately 40% of the study area perimeter (along the north and
west sides) is bordered by forest. The other 60% of the perimeter is tidal. A tidal cove
borders the east portion of the site, and an estuarine channel runs along the southern
boundary. The upstream- most 20 m of estuarine stream at the site is tidally inundated
only at the highest tides, whereas the rest of the channel is typically inundated at every
high tide.
N
Road mortality
survey route
Study area
Figure 2. The study area location and the road mortality survey route. Base photo from
Thurston County Geodata.
The study site includes 1.59 ha of forest and 0.36 ha of open habitat. The forest has
mature trees including grand fir (Abies grandis), big- leaf maple (Acer macrophyllum),
Douglas- fir (Pseudotsuga menziesii), western red cedar (Thuja plicata) and red alder
13
(Alnus rubra). The shrub layer is dominated by sword fern (Polystichum munitum). In
spring the herbaceous layer has dense candyflower (Montia sibirica), water- leaf
(Hydrophyllum sp.) and bleedingheart (Dicentra formosa), most of which die back by late
summer. Abundant coarse and fine downed wood, combined with leaf litter and shrubs
create a complex near-ground structure through most of the forest.
The open habitat is a human-created opening within the forest. It includes areas of
grass/forbs, garden, shrub, and remnant forest/shrub. This area also includes a house,
gravel driveway, and wood chip paths. Interspersed remnant patches of forest exist
within the opening.
Potential predators of the northern red- legged frog that I have observed at the study
site are river otter (Lutra canadensis), mink (Mustela vison), raccoon (Procyon lotor),
great blue heron (Ardea herodias), and garter snake (Thamnophis sirtalis).
Additional animal species that I have observed at the study area that typified the
animal community include black-tailed deer (Odocoileus hemionus), chickaree squirrel
(Tamiasciurus douglasi), northern flying squirrel (Glaucomys sabrinus), opossum
(Didelphis virginianus), barred owl (Strix varia), belted kingfisher (Ceryle alcyon),
winter wren (Troglodytes troglodytes), golden-crowned kinglet (Regulus satrapa),
American robin (Turdus migratorius), black-throated gray warbler (Dendroica
nigrescens), Wilson’s warbler (Wilsonia pusilla), spotted towhee (Pipilo maculatus),
song sparrow (Melospiza melodia), northwestern salamander (Ambystoma gracile), longtoed salamander (Ambystoma macrodactylum), rough-skinned newt (Taricha granulosa),
western red-backed salamander (Plethodon vehiculum), ensatina (Ensatina eschscholtzii),
Pacific chorus frog (Pseudacris regilla), banana slug (Ariolimax columbianus), Western
tiger swallowtail butterfly (Papilio rutulus), and Clodius parnassian (Parnassius clodius).
Non-native species present included: domestic dog, cat, and various slugs.
Demographics
Study Site Set-Up and Location Reference
The study area had a staked 10 by 10 m (100 m2 ) grid established for use with
random selection of visual encounter survey quadrats. I recorded data within each 100
m2 area to an accuracy of 6.25 m2 by locating 1/16 sections within the larger area. I used
14
aerial photography to determine the locations of telemetered frogs that traveled outside
the study area.
Study Site Stratification
The sample design utilized forest and open areas as strata. Within the forest, substrata
(macro- habitats) were shrub, herbaceous, shrub/ravine, shrub/slope to shoreline,
shrub/shoreline cliff, tidal channel, and branch pile. Open area substrata were
grass/forbs, garden, shrub, and remnant forest/shrub.
Off-site forest substrata were shrub/hillslope plateau and shrub/hillside.
Survey Techniques
Time-constrained searches-- Prior to completion of the site grid, I conducted seven
1-hr time-constrained searches April through the end of May 2001. Each survey included
20 min in the open stratum, and 40 min in the forest stratum. Surveys were done by
walking with no specific pattern, but through as much of a stratum as possible within the
indicated time limits, closely observing and listening for any signs of frogs. The netting
on a butterfly net was used to lightly disturb ground and shrub vegetation for a swath ca.
1.5 m, in front and to the sides of the walking path. If a frog was observed, the time was
stopped, and then restarted after data collection on the frog and habitat was completed.
Area-constrained searches-- From June through October 2001, I conducted areaconstrained surveys in the forest and open strata using a stratified random sample design.
Sample quadrats were randomly chosen each week based on the use of an octal table
(Heyer et al. 1994), and I alternated the survey start order between open and forest strata
each week. During each weekly survey, I searched for 6 min in each of nine 100 m2
quadrats in the forest and six 100 m2 quadrats in the open for a total search time of 90
min. The boundaries of quadrats to be searched were typically roped at waist level the
day prior to the survey to provide clear delineation of survey areas.
Surveys were done by walking an inside perimeter corridor and searching a ca. 3 m
swath, and then searching between both sets of opposite corners with a focus on the
interior area of the quadrat, while observing for frogs, and listening for noise that could
be from frog movement. As in time-constrained searches, a butterfly net was used to
lightly disturb ground and shrub vegetation for a swath ca. 1.5 m along the walking path.
15
As time allowed, downed wood was picked up, or lightly jostled, and the area beneath
sword ferns was more closely observed. If a frog was observed, the time was stopped,
and then restarted after data collection was complete.
Drift fence/trap arrays-- I also captured frogs using drift fence arrays. I established
10 arrays. Seven were in the forest, two were in the open area, and one was on the edge
between open and forest strata (Fig. 3). I randomly selected the placement of arrays with
the additional constraints that arrays could not be within 20 m of each other, and that
forest arrays would be dispersed within different sectors of the forest. The latter
dispersion was accomplished based on breaking the full forest area into three ca. equalsized areas which each had two randomly placed arrays, and one area that was ca. ½ the
size of the other three, that had one randomly placed array.
0
10
N 20
Study area boundary
30
40
50
Tidal Cove
60
Distance (m)
70
80
90
FOREST
100
OPENING
110
120
130
Tidal Cove
140
150
160
170
Drift fence/trap array
180
Thermographs - core stations
190
Thermographs - supplemental stations
Tidal Channel
200
0
10
20 30
40
50 60
70
80 90 100 110 120 130 140 150 160 170 180 190
Distance (m)
Figure 3. Locations of drift fence/trap arrays and thermographs.
16
Each array had three drift fence spokes; each spoke was 4 m long and at least 20 cm
high. Spokes were joined at one end in the center of each array and placed at equidistant
angles, with one spoke facing east. I used logs, wood planks, or garden fabric for fence
material. The base of each fence was buried or positioned in a manner to prevent frogs
from traveling under.
Each array included six funnel traps. These traps were placed mid-way along each
side of each fence. I constructed traps from 0.9 cm mesh plastic garden fencing. Each
trap was 70 cm long, had a 20 cm radius, and had a 6 cm wide inverted funnel entry at
each end. I used plastic cups to close the funnels and ensure that animals did not enter
when the traps were not in use. I concealed traps with pieces of old wood, moss, and
clipped sword fern fronds.
From July to November 2001, I opened traps following the completion of weekly
area-constrained searches. My standard protocol was to leave the traps open for 2 days
and during this time, and to check each trap once daily. However, during hot weather, I
only kept traps open for 1 day, and I checked traps in warmer exposed locations twice
daily to lessen the likelihood of trapped animal mortality. In the fall, traps were checked
daily but left open for longer periods of time (maximum 7 days).
Initially, I left traps concealed as described above and investigated for frog catch by
looking into the traps with a flashlight. However, using this method caused me to
overlook three frogs (all the same week), that subsequently died before the next week’s
surveys. After this occurrence, I changed my methodology to completely remove traps
from their concealed location to ensure I found any trapped frogs.
Drift fence arrays were operated for 33 days. All but the first two days included the
full set-up of 10 arrays, with six traps per array, giving an overall trapping effort of 1894
24 hr trap days.
Opportunistic sightings-- The opportunistic sightings survey type included any frog
that I observed at the study area that was not part of the other survey techniques described
above.
Road mortality-- Road mortality surveys were done by foot on 6, 8, 9 and 10
November 2002 along a 0.5 km stretch of road (Fig. 2). I chose this timing as it was after
17
a heavy rainfall during the fall, making it likely that frog movement would be occurring.
I conducted the surveys by closely observing one lane and the road edge while walking
one side of the road, and then doing the same in a return loop along the other side of the
road. All animals found were removed to prevent recounting on subsequent trips. Most
animals were pulverized and dispersed, preventing their measurement and preventing an
exact count. Snout-vent length was measured if possible, and general size categories of
small, medium, or large were used where reasonable. Other amphibian species besides
northern red-legged frogs were recorded during the surveys.
Frog Data and Techniques
Standard data were taken when a frog was observed. These included date and time,
frog measurements, tag number (see below), behavioral observations, habitat
characteristics, environmental measurements, and location. I was not able to catch all
frogs that I observed. I collected data as follows for those frogs that were caught (study
years 2001 and 2002), (1) SVL and shank length to the nearest mm, (2) weight with a 100
g Pesola scale to the nearest 1 g as a mass equivalent, (3) frog gender (or potential
characteristics where I was not able to discern gender), (4) moisture condition (categories
of dry, moist, wet, determined typically by holding the frog: dry was dry to my touch,
moist was some moisture evident, and wet was where a frog exuded water, causing my
hand to drip), (5) condition appearance (ventral skin folds evident versus appearing wellfed and rotund), and (6) behavioral observations. In 2000, only frog location and SVL
were taken. Frog measurements were typically taken at monthly intervals in 2001 if
frogs were recaptured. In 2002, measurements were taken weekly if recaptures occurred.
Using sterile techniques, I inserted a passive integrated transponder (PIT) tag
(Biomark, Inc., 134 N. Cloverdale Road, Boise, ID) under the dorsal skin of all frogs
caught (except those that escaped before I was able to insert the tag). The tags were 125
kHz, 11.5 by 2.1 mm in size. Each tag contained a unique 10-digit alphanumeric code
that allowed individual frogs to be subsequently identified. I used a Destron Pocket
Reader model HS9250L1 which can scan a tag that is within 5 cm, to read the tags.
Captured frogs were held until the end of the survey (typically a maximum time of 3
to 5 hr) in mesh minnow traps, and then released at their capture locations.
18
Environmental Conditions
Environmental Data Taken at Frog Observation Sites
Environmental data that I collected at each frog observation site included (1) air
temperature 1 cm above ground, (2) ground temperature 1 cm below the ground, and (3)
ground surface moisture. Air and ground temperatures at frog sites were taken 5 to 20
min following the frog capture or observation time. Air measurements in 2001 were
taken with a digital thermo- hygrometer (accuracy 0.1 C), and ground temperatures were
taken with a Taylor temperature probe (read to the nearest degree C). In 2002, a model
Temp 5 Oakton electronic thermometer (accuracy 0.2 C) with probe was used for all
temperature measurements.
Ground surface moisture was determined using the following scale: (1) dry, no
evidence of moisture; (2) moist, soil color looks damp and soil feels damp to the touch;
and, (3) saturated with soil visibly full of water and wet to the touch.
Study Site Environmental Measurements
Additional data were taken to provide a broader characterization of survey quadrats
and the study area. These measurements included (1) quadrat moisture condition, (2) air
and ground temperature, (3) precipitation, and (4) tidal channel salinity. In addition, offsite precipitation and air data were obtained.
Quadrat ground moisture condition-- Quadrat moisture condition was determined
during area-constrained searches through visual observations of surface moisture, and by
examining leaf duff and wood to check for indications of moisture. I visually estimated
the ca. surface area percent of the quadrat that contained moisture.
Temperature -- Continuously recording thermographs were installed at the study area
to characterize differences between strata, and between ground and air, and one branch
pile. Air thermographs were installed at three “core” sites on 4 June 2001 to provide
broad scale coverage of near shoreline, in forest, and open (near garden) study area
conditions. On 9 August 2001, ground thermographs were added to the core sites, and
“supplemental” thermographs were additionally installed at three locations where frogs
had been observed (Fig. 3). Table 2 provides information on thermograph make, model,
settings, and field deployment locations. Air temperature data from The Evergreen State
College were used for dates that preceded the installation of study site thermographs.
19
Table 2. Thermograph and station characteristicsa.
Location
Core
b
Open site A
c
Open site A
d
Forest site A
e
Forest site A
f
Forest site B
g
Forest site B
Supplemental
h
Forest site C
i
Forest site C
j
Forest site D
k
Forest site D
l
Forest site E
m
Forest site E
Roving
Description
Type
Stratum
Near garden
Near garden
Near shoreline
Near shoreline
In forest
In forest
Air
Ground
Air
Ground
Air
Ground
Cliff at shoreline
Cliff at shoreline
Ravine
Ravine
Edge branch pile
Edge branch pile
Air
Forest
Ground Forest
Air
Forest
Ground Forest
Air
Forest
Under pile Forest
Air
All
Start
End
Make
Model
Open 4-Jun-01 11-Jan-02 Onset Stowaway XTI
Open 9-Aug-01 11-Jan-02 Onset Optic Stowaway
Forest 4-Jun-01 11-Jan-02 Onset Stowaway XTI
Forest 9-Aug-01 11-Jan-02 Onset Optic Stowaway
Forest 4-Jun-01 11-Jan-02 Onset Stowaway XTI
Forest 9-Aug-01 11-Jan-02 Onset Optic Stowaway
9-Aug-01 11-Jan-02
9-Aug-01 11-Jan-02
9-Aug-01 11-Jan-02
9-Aug-01 11-Jan-02
9-Aug-01 11-Jan-02
9-Aug-01 11-Jan-02
9-Aug-01 11-Jan-02
Onset
Onset
Onset
Onset
Onset
Onset
Onset
Optic Stowaway
Optic Stowaway
Optic Stowaway
Optic Stowaway
Optic Stowaway
Optic Stowaway
Optic Stowaway
a
Settings for all instruments: interval frequency 1 hr, 100 points, average mode. Pre and post
calibration results excellent. All instruments within 0.25 C of each other.
b
Installed 20 cm above ground, 100% cover, site with remant vegetation.
c
Buried 4 cm under soil, plus under 7 cm of light duff, site with remnant vegetation.
d
On tree side 20 cm high, 100% shade. Site has slight slope aspect toward cove.
e
Buried 4 cm under soil, plus under 7 cm of light leaf duff. Slight slope aspect toward the cove.
f
On post 20 cm from ground. Partial sun, probe case covered with leaves for additional shade.
g
Buried 4 cm down in soil, plus under 6 cm of light duff. Partial sunlight.
h
Placed in opening under root wad. This site 2.0 m above mudflats, in overhanging ledge on 3.0 m
high cliff. Site faces SE to mouth of tidal channel.
i
Buried 4 cm under soil and 6 cm of leaf duff. Rest same as for note h.
j
Placed at top of duff (16 cm deep) on tree. Site has south aspect. Instrument is 5.0 m from
stream, 3.5 m high on side of ravine.
k
Buried 4 cm under soil and under 10 cm of leaf duff. Rest same as for note j.
l
Placed 4 cm above ground, shaded by large down wood.
m
Under old branch pile. Instrument inserted 60 cm deep into middle of pile, close to ground.
Pile is 0.7 m high, 4.0 m long and 1.2 m wide.
Thermographs were calibrated according to Schuett-Hames et al. (1999). All
temperature equipment was checked against a certified reference thermometer (HB model
23421) to ensure instrument accuracy.
Precipitation-- The primary source of precipitation data was the weather station at
The Evergreen State College, 3.5 km southeast of the study area. I estimated missing
records using data from the National Weather Station gage located at the Olympia
Airport, 15.5 km southeast of the study site.
20
Tidal channel salinity-- I used a Hach conductivity meter, model 2510 with an
accuracy of +/- 2% of full scale to measure salinity. I took salinity measurements during
an incoming tide at 12 locations within the flowing channel that forms the southern
boundary of the study site, each at 10 m intervals longitudinally along the channel.
Samples taken at distances 100 m and 110 m were of incoming tidal waters, all other
stream samples were taken upstream of tidal waters. I also took samples from five pits
(dug for this purpose) within 2.5 m of the flowing stream and within the tidal zone, to
represent potential locations where a frog might sit. The pits were left to fill through
subsurface infiltration for 1 hr before sampling.
Salinity readings were taken in micromhos/cm and converted to mg/l sodium chloride
through use of a conversion chart provided with the instrument. For analyses, this data
was further converted to ppt sodium chloride.
Flow was estimated at the upstream end of the channel within the study area using a
rough approximation of flow depth, width, and velocity.
Terrestrial Natural History and Behavior
Radio Telemetry
I attached radio transmitters to 10 frogs between mid-July and the end of December
2001. No more than two or three frogs were tracked simultaneously. I used standard
(BD-2G) and temperature sensitive (BD-2GT) transmitters (Holohil Systems, Ltd., 112
John Cavanaugh Road, Carp, Ontario, Canada KOA 1LO). An external waist belt was
used to attach transmitters to frogs. It was made of either satin ribbon (0.3 mm to 0.6 mm
wide) or bootlace material (0.7 mm wide) sewn to a custom-sized fit on each frog.
Varying transmitter/belt combinations weighed 2.0 g to 2.5 g.
Transmitters can impede frog movement, potentially affecting frog behavior, so
transmitter mass should not exceed 10% of an animal’s mass (Richards et al. 1994).
Based on this I attached radios only to frogs with a mass
30 g ( 7% of frog mass). I
radio-tagged only females because no males were large enough to meet the criterion. In
my original study design, I had planned to use only frogs found during trapping or areaconstrained searches, but due to the difficulty in finding enough suitably sized frogs, I
ended up using any frogs found that met the mass criterion.
21
Abrasion from attached belts can cause open sores on anurans (Rathbun & Murphey
1996; Chan-McLeod 2003). I treated the first signs of dorsal abrasion with antibiotic
cream (Neosporin, Polymyxin B Sulfate – Bacitracin Zinc – Neomycin Sulfate). If sores
reached
3 mm in length, I removed the telemetry gear.
I located telemetered frogs typically once a week using a Telonics Model RA-14
antenna with a Telonics TR-4 receiver. Either apparent loss of reception from selected
transmitters or inability to find frogs (i.e., reception occurred but the frog could not be
found) led to less frequent data collection intervals in some cases. Intensive effort on
additional days (such as during video data collection) also occurred. During October to
December 2001, with assistance from Washington Department of Fish and Wildlife
personnel, frog locations were checked as often as daily to better resolve possible
seasonal movements.
Video
Video data were taken of frogs in undisturbed locations and postures on 13 and 26
August, and 4, 13, 17 September (late summer), and 23 September (early fall) 2001.
During these sessions, four different frogs were taped. One of these frogs was observed
on 3 days, one on 2 days, and two each on 1 day.
A Sony 24x Digital Zoom 8 mm camera, model CCD-TRV21 was used. The camera
was attached to a tripod, and set up 1.5 to 7.0 m away from an individual frog, which was
beyond the typical flight distance I observed of ca. 0.5 m. Using the zoom function, the
frog was brought into close-up view, with between 10 and 20 cm of surrounding habitat
also visible. After set-up, I left the area to reduce the likelihood that human presence
affected frog behavior, and typically returned once per hour to assure that the frog was
still in the observation area and that the camera was still running. Video footage was
taken until the tape or battery ran out, the frog left the video location, or it became too
dark for observation.
Frog Data and Techniques
Standard data were taken when a frog was observed as described earlier. Additional
observations included a description of movement behavior (e.g., number of hops) if the
22
frog had moved when I approached. If the frog was observed in an undisturbed location,
body posture and structural location (e.g., on ground or elevated on fern) were described.
Habitat Data Taken at Frog Observation Sites
Habitat characteristics recorded were (1) stratum and sub-stratum (described earlier),
(2) microhabitat (i.e., a brief description of the 5 cm area around the frog), (3) distance to
the stratum edge if it was within 5 m, and (4) distance to and description of refuge habitat
containing complex vegetative or wood structure.
Data Analysis
Demographics
Catch per unit effort (CPUE)-- I calculated CPUE for time and area-constrained
searches for spring, early summer, mid-to- late summer, early fall, and mid-fall.
Population numbers -- Estimates were developed for 2001 data using three methods.
1. The number of frogs caught during area-constrained searches was expanded to the
full study area by multiplying the number of frogs per sample quadrat in each stratum by
the number of quadrats in the stratum, and the n adding the totals for the two strata
together. This was accomplished for each survey week, and the sum for the week with
the largest extrapolated value was used for the population estimate.
2. The total number of uniquely identified frogs from all survey types in 2001 was
determined. This was derived from a direct count of PIT tagged individuals and nontagged trap mortalities.
3. A Schnabel mark and recapture population estimate based on recaptures of PIT
tagged frogs was performed. Tag and non-tag data from area-constrained searches and
from frogs found opportunistically during area-constrained search days were used for the
Schnabel population estimate (following Smith 1974). This method allows for
accumulation of captures and recaptures. One cond ition of the method is that the
population be closed, but because some of the study frogs were likely migratory, I cannot
assume this condition was met. Confidence intervals for the Schnabel estimate were
based on Hall (1992).
23
Capture rates in open versus forest strata-- I used a non-parametric Wilcoxon
Rank Sum Test to evaluate whether rates of frog capture for the two strata (forest, open)
were significantly different.
Size, gender and age-- Analysis of size, gender and age was done only for those
frogs that were caught, and with the exception of three frogs from 2000 that lacked PIT
tags, all data was for frogs to which I gave unique marks. In the analysis of these
parameters I assume that the untagged frogs were not recaptured.
I found gender difficult to determine. I identified the larger, round-shaped frogs as
females, however, I was unable to determine the gender for many frogs of small and
intermediate sizes. Hayes (pers. comm. 2001, 2002) identified the gender of two frogs. I
based positive identification of males on the presence of darkened thumb-pads. During
data analysis I further identified any frogs that were > 69 mm and not already identified
to gender, as females, based on Nussbaum et al. (1983).
I computed annual changes in SVL and mass for frogs with more than one year of
data using measurements with the closest dates to a one-year interval. I computed
within- year SVL and mass growth rates for frogs with more than one measurement date
over a minimum interval of 4 weeks. To do this, I used the earliest and latest (through
mid- fall 27 November) measurements within the year for each frog. I normalized both
sets of data by computing a daily rate.
I used a t-test based on unequal variances to determine the significance of differences
between within- year and annual SVL growth rates.
Environmental Conditions
Seasons -- Seasonal periods used in analyses were based on the standard dates for
spring, summer, fall and winter. I further divided the seasons (e.g., early summer) based
on visual analysis of the 2001 temperature and precipitation data, for intervals where the
environmental conditions were changing.
Study area moisture conditions -- I analyzed the percent of open and forest habitat in
the study area that contained ground level moisture (i.e., moist soil, humus, leaf-duff, low
plants and downed wood) for bi-weekly intervals from early April to late December
2001. For this analysis, I utilized quadrat moisture conditions from area-constrained
surveys (June through late October 2001), and developed a mean moisture condition for
24
each survey, for both open and forest habitat, and then developed the mean for the biweekly periods by averaging the means from each consecutive two adjoining weeks. For
time intervals before and after the completion of area-constrained surveys, I relied on
field notes and precipitation data to estimate the ground moisture condition.
Air and ground temperature variances-- I used a two sample F-test for variances to
determine whether the mean daily maxima for the ground for the three core stations
fluctuated less than the mean daily maxima for the air at the three core stations. Data
tested were from 9 August to 31 December 2001.
Natural History and Behavior of Terrestrial Northern Red-Legged Frogs
Fall movement patterns -- I computed the ratio of newly captured and tagged frogs
within each season, to the total number of uniquely identified frogs caught within that
season, to discern movement into the study area by frogs in the fall. I also used seasonal
differences in catch per hour for area-constrained searches to infer whether fall
movement might be occurring.
Active season and winter home ranges-- Active season home ranges were
developed as follows. A length was determined for the distance between the two
observation points furthest from each other. A maximum width was determined by
taking the greatest width (perpendicular to the maximum length line) of the polygon
drawn around all observation points.
Video-- I transferred 8 mm imagery to VHS and analyzed frog movement by
observing the images on a VHS equipped television. I briefly described each frog
movement. Time, behavior category (based on a system I developed for this study), and
movement duration in seconds were determined. Total time for each frog observation
period was determined through a time stamp on the footage, or through the embedded
time system in the tape. Many activities occurred in
allocated a minimum of 1 sec for data analyses.
25
1 sec, but all activities were
CHAPTER 3. DEMOGRAPHIC RESULTS
Based on all survey types except telemetry, I recorded a total of 116 frog sightings or
captures in 2001 (Appendix A). Of these, nine were from time-constrained searches, 29
from area-constrained searches, 69 from opportunistic encounters, and nine from traps.
In this chapter I report population numbers for 2001 using three different analyses:
CPUE for time and area-constrained surveys, a direct count of uniquely identified
individuals, and a Schnabel mark and recapture population estimate. I also report size
and gender data for a longer interval (2000 to 2002), and provide limited data on frog
age, deformities, and mortality.
Population Numbers (Year 2001)
CPUE
The CPUE1 combined average for all time-constrained and area-constrained searches
was 1.0 frog per hour (Table 3). Area-constrained searches had a lesser overall CPUE of
0.9 frogs per hour. Seasonally, I observed substantial changes in CPUE among the five
time intervals where area-constrained searches could be compared. Mid- fall (CPUE 1.5)
was the most productive interval. This was followed by early summer (CPUE 1.0), early
fall (CPUE 0.9), and mid-to- late summer (CPUE 0.8), which had similar values. Spring
(CPUE 0.4) had the lowest value among area-constrained intervals.
Drift Fence Catch
Drift fence efficiency was low (Table 4). Nine frogs were captured in the traps for a
mean of 4.8 frogs per 1000 trap days. Five of the frogs were caught in the same array
(located in the forest near the shoreline) in the fall; of these, four were caught in the same
trap. The two western-most arrays in the forest caught frogs in late summer (two frogs
were caught at different traps in one array, and the other array caught one frog). These
latter three trapped frogs escaped my detection and died in the traps. In early fall, an
array in the open stratum caught one frog. Between 16 October and the termination of
trapping on 5 November, frogs were only observed through trap catch (n = 3), or through
telemetry.
1
In this context, catch also includes frogs that were observed but which evaded capture.
26
Table 3. Time-constrained and area-constrained search catch per hour (2001).
No.
Surveys
All time-constrained and area-constrained surveys
a
1.5
42.0
43
1.0
3
1.5
4.5
2
0.4
2
7
5
1.5
1.5
1.5
3.0
10.5
7.5
3
8
7
1.0
0.8
0.9
4
21
1.5
1.5
6.0
31.5
9
29
1.5
0.9
Early Summer
Mid to Late Summer
Early Fall
a
Catch/
Hour
28
Area-constrained only
Spring
Mid Fall
Totals for area-constrained surveys
No. Hours/ No. Hours No. Animals
Survey
Total
Total
Time-constrained surveys were before 4 June and were each 1 hour. For this calculation, the pre 4 June
number of animals was multiplied by 1.5.
Table 4. Drift fence catch per trap day (2001 data).
No. Survey
No.
No. Trap No. Animals Catch/
a
Days
Traps Days Total
Total
Trap Day
Early Summer
Mid to Late Summer
Early Fall
Mid Fall
Totals for all survey days
2
7
9
15
33
17
60
60
60
60
34
420
540
900
1894
0
3
2
4
9
0.0000
0.0071
0.0037
0.0044
0.0048
a
Trap surveys were 1 day (24 hours) each. On 3 July, 14 traps were used; on 4 July,
20 traps were used. All other days had 60 traps.
Area-Constrained Catch Totals
A total of 29 frogs were caught (or
observed) during the 21 areaconstrained surveys (Fig. 4, Appendix
B). These data do not differ
significantly from a Poisson
distribution (Chi-square test: ÷2 =
0.8070; p = 0.6669).
7
6
5
No. of 4
surveys 3
2
1
0
0
Based on area-constrained catch
results, I caught a mean of 1.38 frogs
per survey with 95% confidence limits
1
2
3
4
5
6
No. of frogs
Figure 4. Frequency distribution: number of frogs
found during 2001 area-constrained searches.
27
of 0.65 and 2.11. When samples were extrapolated to the entire study area (i.e., 195 100
m2 quadrats), the mean number of frogs represented was 18, but the weekly-extrapolated
numbers ranged from 0 to 78 (Appendix B).
Frog Observation Numbers Open Versus Forest
I had a higher rate of frog capture (and non-capture observations) during areaconstrained searches in the open versus the forest habitat strata (Appendix B). The mean
number of frogs located per 100 m2 quadrat was 0.12 in the open stratum (i.e., 1 frog for
every 833 m2 searched) and 0.07 in the forest (i.e., one frog for every 1,429 m2 searched).
Due to the large number of surveys with no catch (62% of forest surveys and 48% of
open stratum surveys), catch data were extremely skewed. The capture rate in the open
habitat was not significantly greater (p = 0.14) than that in the forest.
Frog Numbers Based on Unique Identification
In 2001, I recorded 51 different frogs using unique PIT tag marks. With the addition
of three non-tagged frogs found dead in traps, I estimated a minimum population size of
54 frogs.
Schnabel Mark and Recapture Population Estimate
Through all study methods, the
35
30
51 tagged frogs were involved in
84 captures for 2001. Figure 5
shows the frequency of capture for
tagged frogs (excluding data from
25
No. of
tagged 20
frogs 15
6
5
0
were captured just once. A total of
1
2
3
1
1
0
1
4
5
6
7
No. of times captured
14 frogs were captured two or
frogs were captured four, five and
8
10
telemetry). Most frogs, (n = 34),
three times. Additionally, three
34
Figure 5. Frequency of tagged frog capture through all
survey types, during 2001.
seven times.
Due to the overall low recapture frequency of tagged frogs, I utilized all data for frogs
that were captured on area-constrained search days for the Schnabel population estimate.
28
Thus a total of 35 frog observations including seven recaptures were used for the analysis
(Appendix C).
The mark-recapture analysis indicated a maximum study area population estimate of
60 (95% confidence interval of 60 +/- 81) frogs for 15 October 2001 (Table 5). This was
based on 25 marked individuals and seven recaptures over the analysis interval.
Table 5. Schnabel population estimates (using frog observations from area-constrained
search days in 2001).
Date
4-Jun
18-Jun
25-Jun
16-Jul
30-Jul
6-Aug
13-Aug
20-Aug
26-Aug
3-Sep
10-Sep
17-Sep
24-Sep
30-Sep
8-Oct
15-Oct
A
B
No.
Caught
No.
No. Marked
Marked
in Area
(A)*(B)
1
2
2
2
1
2
1
1
6
4
1
2
2
4
3
1
C
1 ----------------- --------------2
1
2
1
3
6
1
4
8
1
5
5
1
6
12
1
7
7
1
8
8
5
9
54
3
14
56
1
17
17
0
18
36
2
18
36
2
20
80
3
22
66
1
25
25
(A)*(B)
Sum
RecapSum of
tures Recaptures
(A)*(B) Sum/
(C)
Est. Pop.
0 ------------------------------------------------------2
0
0 -------------------8
0
0 -------------------16
1
1
16
21
0
1
21
33
1
2
17
40
0
2
20
48
0
2
24
102
0
2
51
158
1
3
53
175
0
3
58
211
2
5
42
247
0
5
49
327
2
7
47
393
0
7
56
418
0
7
60
Summary of Population Estimates
The three estimates of the study population size are similar (Table 6). The direct
count of uniquely identified animals provided the lowest value. Analysis of seasonal
ratios of newly tagged frogs (Table 7) indicates that new frogs were found at a rate of
50% or higher throughout the study.
Table 6. Population comparison (2001).
Method
Total Frogs Est.
95% C.I.
Area-constrained searches weekly estimates
a
Direct count of uniquely identified frogs
Schnabel estimate
0 - 78
54
60
+/- 81
a
PIT tagged individuals and three frogs found dead in traps.
29
Table 7. Ratio of newly tagged versus total number of frogs caught seasonally (2001).
Total No. Frog
Captures a
No. of Frogs Newly
Tagged
Ratio
New/Total
20
20
27
17
15
10
15
11
0.75
0.50
0.56
0.65
Spring - Early Summer (2 May - 8 Jul)
Mid - Late Summer (9 Jul - 21 Aug)
Early Fall (22 Aug - 24 Sep)
Mid - Fall (25 Sep - 3 Nov)
a
May have more than one recapture per frog. Note: on 21 August three no-tag frogs died in traps. Because
they were unable to become part of the tag data set, they were not included in these numbers. In addition,
frogs found and caught through telemetry are not included.
Maximum population estimates based on area-constrained searches (n = 78) and the
Schnabel estimate (n = 60) were both larger than the direct count. Figure 6 shows that
between 26 August and 15 October, the Schnabel estimates cluster between 42 and 60
frogs. The peak of 78 on 30 September from the area-constrained surveys estimate is
90
80
70
60
50
40
30
20
10
0
22-Oct
8-Oct
24-Sep
10-Sep
27-Aug
13-Aug
30-Jul
16-Jul
2-Jul
18-Jun
Area-constrained expanded catch
Schnabel population estimate
4-Jun
Estimated no. of frogs
also in the same time interval.
Date (2001)
Figure 6. Comparison between area-constrained data expanded to the full study
area, and the Schnabel population estimate.
Size, Gender, and Age
Gender, lengths, weight, and, where possible, an estimate of age for frogs caught
during 2000 to 2002 are provided in Appendix D Table D-1. I made 136 measurement
episodes on frogs. Of these, I measured 56 frogs only once. The remaining 80 episodes
involved repeated measurements on 24 different frogs. In 2000, SVL was the only
measurement taken. From 2000 to 2002, I obtained 135 SVL, 113 shank measurements,
30
and 115 masses. Gender was identified on 25 different frogs: three were males and 22
were females.
SVL
Frog SVL ranged from 36 to 79 mm. The SVL of known females during 2000 to
2002 ranged from 49 to 79 mm. The mean of the maximum SVL measured for known
females in 2001 was 69.3 (n = 16; s = 3.0). The SVL of known males ranged from 51 to
59 mm (mean of the maximum yearly SVL 2000 to 2002 = 55 mm, s = 3.5, n = 5 1 ).
Figure 7 shows SVL data. Known females comprised the larger frogs, whereas
known males fell into the middle and lower portions of the size range. The SVL
measurement history for 23 frogs (nine females, three males, and 11 of unknown gender)
illustrates growth.
80
75
70
Length (mm)
65
60
55
50
45
40
Gender unknown
Known females
Known males
Au
g0
Se 0
p00
O
ct
-0
0
No
v00
De
c00
Ja
n01
Fe
b01
M
ar
-0
1
Ap
r-0
1
Ju
n01
Ju
l-0
1
Au
g01
Se
p01
O
ct
-0
1
No
v01
De
c01
Ja
n02
M
ar
-0
2
Ap
r-0
2
M
ay
-0
2
Ju
n02
Ju
l-0
Au 2
g02
Se
p02
O
ct
-0
2
No
v02
35
Figure 7. Red-legged frog snout to vent length measurements by gender, August 2000
through November 2002. In addition, the length growth patterns for 23 frogs with repeat
measurements are indicated.
1
One male was measured in 2000, 2001, and 2002.
31
Growth data are within-year and multi- year. Six frogs had multi- year SVL data (Fig.
7; Appendix E Table E-1). Of these, four females with recaptures spanning two years
had a mean annual growth of 13.1 mm (range: 9.92 to 15.29 mm). One male caught in
each of the three survey years grew 3.2 mm between 2000 and 2001, and 3.3 mm
between 2001 and 2002. A frog of unidentified gender grew 13.9 mm between 2000 and
2001. The mean annual growth for all six frogs was 10.37 mm (range: 3.19 to 15.29
mm), equivalent to a mean daily growth of 0.03 mm (range: 0.01 to 0.04 mm).
I had within- year SVL growth data for six females (one had data for each of the 2
years), one male, and six frogs of unknown gender (Fig. 7; Appendix E Table E-2). The
mean daily growth for females was 0.06 mm (range : –0.01 to 0.14 mm, n = 7), for the
one male 0.11 mm, and for frogs unidentified to gender 0.11 mm (range: 0.05 to 0.21
mm). The mean daily growth for all frogs with within-year growth data was 0.09 mm
(range: –0.01 to 0.21 mm) and was significantly greater than the annual rate (expressed as
a daily rate) (Student t-test: p = 0.0023).
Shank Length
Shank lengths ranged from 21 to 45 mm (Appendix D Table D-1). Those of known
females during 2001 to 2002 ranged from 28 to 45 mm. The mean of the maximum
shank length measured for 15 known females in 2001 was 40.2 mm. Three known males
in 2001 to 2002 had shank lengths that ranged from 30 to 36 mm.
Mass
Frog masses ranged from 3 to 48 g (Fig. 8; Appendix D Table D-1). May to
November 2001 the masses of most frogs clustered between 10 and 36 g, and fewer data
for 2002 showed a similar pattern. Larger frogs were female, and the masses of males
overlapped little with known females. Small frogs (5 to 6 g) appeared in late July and
early August 2001, and only large frogs (35 to 48 g) were found November through
December 2001.
The masses of known females during 2001 to 2002 ranged from 11 to 48 g. The mean
of the maximum mass measured for known females in 2001 was 35.8 (n = 16; s = 5.4).
The masses of known males ranged from 11 to 23 g. Of the two known males in 2001,
one was 16 g and the other was 23 g (s = 5.0).
32
50
45
40
35
Mass (g)
30
25
20
15
10
Gender unknown
Known females
Known males
5
2
11
-N
ov
-0
ct
-O
11
-0
2
2
2
10
-S
ep
-0
2
-0
ug
-A
10
10
-J
ul
-0
02
2
nJu
9-
9-
M
ay
-0
2
2
r-0
-0
Ap
8-
ar
M
8-
5-
Fe
b-
02
02
1
5-
Ja
n-
-0
1
-0
ec
D
5-
ov
N
4-
ct
-0
1
01
4-
O
p-
01
Se
3-
3-
Au
g-
l-0
1
01
Ju
3-
n-
-0
Ju
2-
ay
M
2-
1-
Ap
r-0
1
1
0
Figure 8. Red-legged frog weights by gender May 2001 through October 2002. In addition,
the weight (mass) histories for frogs with more than one measurement point are indicated
by lines that connect measurement points.
The measurement histories for 20 frogs with greater than one mass measurement indicate
growth (Fig. 8). Appendix E Tables E-3 and E-4 provide analyses of multi- year and
within- year mass data. For two female frogs that each had a year’s data, the mean yearly
increase in mass was 13.5 g (range: 12.4 to 14.5 g; daily increases in mass were 0.03 and
0.04 g). However, the one male with data over ne arly a year lost 1.0 g, and therefore
showed no daily mass increase.
In contrast, for 13 frogs where within- year data were taken, the mean daily increase in
mass was 0.08 g (s = 0.01). The six known females had a mean daily increase of 0.08 g
(s = 0.07), the single known male’s daily increase was 0.16 g, and six frogs of unknown
gender had a daily increase of 0.06 g (s = 0.04).
33
SVL and Mass Relationships
Mass varies with SVL (Fig. 9). Notably, the relationship between mass and SVL of
known females > 64 mm was widely variable (Fig. 9a). This variability however was not
evident in spring as compared to summer through early winter (Fig. 9b).
(a) By Gender
50
45
40
35
30
Mass
(g) 25
20
15
Known females
Known males
Gender unknown
10
5
0
35
40
45
50
55
60
65
70
75
80
Snout-to-vent length (mm)
50
(b) By Season
45
40
35
30
Mass
(g) 25
20
15
Spring
10
Early summer through early fall
5
Mid-fall through early winter
0
35
40
45
50
55
60
65
70
75
80
Snout-to-vent length (mm)
Figure 9. Northern red-legged frog snout-to-vent length and mass, by gender (a), and by
season (b).
34
Deformity and Mortality Characteristics
Deformities or Injuries
I rarely encountered frog deformities or injuries. During 2000 I observed no frogs
with abnormalities. During 2001 I found one frog that was missing an eye, and during
2002 I found one frog with no right hand and misshapen digits on its left hand. Based on
the number of PIT-tagged frogs in each year, this represented an injury/deformity value
of 2% for 2001 (nPIT = 51), and 6% for 2002 (nPIT = 16).
Mortalities
The only mortality I recorded on the study site involved three frogs that I found dead
that had been caught in traps on 21 August 2001.
Fourteen piles of raccoon scat scanned with the PIT tag reader revealed no evidence
of expelled PIT tags. I found no indication of mortality among telemetered frogs over the
time interval (2 May 2001 to 29 December 2001) that I followed them.
However, using telemetry, I located a fall migration pathway used by at least some
frogs from the study site. This pathway crosses a residential road. Between 6 and 10
November 2002 I found a minimum of 15 dead red-legged frogs on a 0.5 km survey
stretch of this road (Fig. 2). The exact number was difficult to discern as most of the
frogs were not intact. I also found 34 dead Pacific chorus frogs (Hyla regilla), one dead
ensatina (Ensatina eschscholtzii), and one dead rough-skin newt (Taricha granulosa)
during the same period.
35
CHAPTER 4. ENVIRONMENTAL CONDITION RESULTS
This chapter includes year 2001 temperature, moisture, and channel salinity results.
Study Site Temperature and Moisture Conditions
Seasonal Variation
Temperature and rainfall varied spring through early winter at the study site (Fig. 10).
Early summer had the lowest seasonal percent of days with rain (17), and mean daily
rainfall and air temperature values fell between values found in spring, and mid-summer
through early fall.
61
Spring (20-Mar to 20-Jun)
Early summer (21-Jun to 8-Jul)
Mid-summer through early fall (9-Jul to 24-Sep)
Mid-fall through early winter (25-Sep to 31-Dec)
41
22
17
15.0
12.3 13.9
2.3
Days with rain (%)
1.9
l 7.2
l
l
l
Av air temperature (C)
l
l
4.6
0.8
Av rainfall/day (mm)
14.4
9.0
Av ground temperature (C)
Figure 10. Seasonal precipitation and temperature regime at the study site in 2001.
The driest, warmest study interval was the 78-day mid-summer through early fall
period; the mean air temperature was 15.0 C and the mean precipitation was 0.8 mm/day.
The 98-day mid- fall through early winter period was the wettest of the study; mean
precipitation was 6 mm/day and 61% of days had rain. A sharp drop in the mean air and
ground temperatures occurred during this period. Appendix F Table F-1 provides greater
detail on the variation in seasonal conditions.
Figure 11 illustrates precipitation, and air and ground temperatures during the 2001
study period. I recorded higher temperatures during extended periods of reduced
precipitation. The only substantial precipitation event that occurred between midsummer and early fall occurred 21 to 24 August. During this 4-day interval, 53.9 mm of
rain was recorded. For the prior 54 days a total of only 5.9 mm had fallen, and only 1.5
36
60
55
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Total rainfall 3.5 km from the study site (mm)
Daily max of the averaged hourly values for 3 air
temperature core stations (C)
Daily max of the average of 3 core sites ground
temperature (C)
50
45
Rainfall (mm)
40
35
30
25
20
15
10
5
20-Mar
27-Mar
3-Apr
10-Apr
17-Apr
24-Apr
1-May
8-May
15-May
22-May
29-May
5-Jun
12-Jun
19-Jun
26-Jun
3-Jul
10-Jul
17-Jul
24-Jul
31-Jul
7-Aug
14-Aug
21-Aug
28-Aug
4-Sep
11-Sep
18-Sep
25-Sep
2-Oct
9-Oct
16-Oct
23-Oct
30-Oct
6-Nov
13-Nov
20-Nov
27-Nov
4-Dec
11-Dec
18-Dec
25-Dec
0
Date
Figure 11. Precipitation, and air and ground temperatures during spring through early winter 2001.
37
Temperature (C)
65
mm of rain fell for the 31 days following this rain event. Rain of the magnitude of the 21
to 24 August storm did not recur until the second half of October. The heaviest rainfall
during the 2001 study period occurred 10 to 16 November. The total rainfall for this
event was 124.0 mm; the peak daily value was 61.2 mm on 14 November.
On 28 November 2001, ca. 21 cm of snow fell at the study area and at a nearby
location where two telemetered frogs had moved. By 2 December, the snow had melted
in exposed areas, but some remained several days longer in shaded locations.
Ground/Surface Moisture
Moist ground (e.g., soil, leaf litter, low growing herbaceous plants such as mosses,
and downed wood) at the study site had ca. 100% area coverage in the spring, and from
mid-October through December. However, during early summer through mid-October
droughty, warm conditions, the forest and open habitat were less moist (Fig. 12). In early
summer the surface moisture began to dry, but moisture could be found in the soil, and in
humus and leaf litter under the skirt of sword ferns as well as in downed wood. As the
summer progressed, the soil and humus dried, and by 23 July, leaf litter under the sword
Open % moist
Forest % moist
1 14
29 5 to -Ap
-A
r
pr 28to Ap
13 12- r
M
27 to
a
-M 26 y
ay -M
to ay
10 9J
24 to 2 un
-J
3
un -Ju
to n
8 722 t o J u l
-J 2 1
ul
to J u l
4
5
1 9 to A u
- A 18 g
u g -A
t o ug
2 1-S
to
ep
16 1530 t o S e
-S 2 9 p
ep
-S
to e p
1 13
2 8 4 to - O
ct
-O
2
c t 7-O
to
c
1 1 10- t
25 t o No
-N 2 4 v
ov - N
to o v
9 8-D
to
e
22 c
-D
ec
100
90
80
70
60
50
40
30
20
10
0
1
to
Mean % moist area
ferns was no longer moist.
Figure 12. Bi-weekly estimated mean moisture conditions in the study area open and
forest habitats in 2001.
38
Interestingly, and evident in Figure 12, was that throughout the droughty part of the
2001 study, I observed a pattern of open habitat having more moisture available than
forest habitat. In addition, tidal shoreline remained permanently moist or flooded through
this interval. During mid-summer (9 July) through mid-October, intermittent rains
remoistened the ground surface, but this was typically spotty (e.g., 0.25 mm of rain on 15
July 2001 only reached the ground in locations in the forest where there were tree gaps).
As early as 9 July, in the early morning, open grass and forbs habitat had dew and
guttation moisture, whereas the forest did not. For example, on 20 August, open habitat
quadrats with grass and forbs had 60 to 80% of their surface area with dew and guttation
moisture, whereas in forest quadrats I only found moisture on the underside of downed
wood (ca. 1% of the quadrat surface).
By 13 August the forest and open habitats were predominantly dry. On this date I
estimated that only 1% of the ground area within the forest quadrats was moist; the only
moisture I found in the day’s area-constrained nine forest survey quadrats was along the
bottom of downed wood, and in an area of creeping buttercup (Ranunculus repens). On
this same day I found moisture in 3% of the open habitat quadrats surveyed. These moist
areas were similarly in downed wood, and in an area of creeping buttercup.
By early fall, rains began to re- moisten leaf litter in the forest while the soil remained
dry. As the sun angle became lower in the fall along with cooler air temperatures, a ca.
10 by 30 m area of the open habitat with grass and forbs no longer received sun and
became constantly moist to saturated from cumulative days of accumulating dew and
guttation moisture. On two occasions in the fall (22 and 24 September), I observed fog
drip (i.e., the forest trees intercept and accumulate fog until it drips similar to a light
rainfall) in the forest. This was coincident with warm days and cool nights. In midOctober, the soil below leaf litter began to re-moisten. Under sword fern skirts, the top
layer of leaves had become moist, but the inner core area of leaves was still dry.
Leaf-Fall
Big- leaf maple leaves began to fall in early September. On 8 October, ca. 30% of the
forest floor was covered with new leaf- fall from both maple and alder trees. By 15
October, ca. 90% of the forest floor was covered with new leaf litter. At the end of
October, 75% of the leaves were off of the trees, and completion of leaf- fall occurred late
November.
39
Air and Ground Temperature Relationships
A prominent pattern found was that ground temperatures (as daily maxima) fluctuated
less on a day-to-day basis than did the daily maxima air temperatures (F-test two sample
for variances, p < 0.0001). In addition, air temperatures were typically warmer than
ground temperatures summer through early fall, but beginning in mid-fall, ground
temperatures became warmer than air temperatures with increasingly greater frequency.
By late fall, ground temperatures were almost always greater than air temperatures.
Figure 13 shows the detail of this reversal for the three core temperature stations.
Table 8 presents air and ground temperatures for the three core temperature stations
and the three supplemental stations. The open habitat site had the highest maximum air
and ground temperatures for the late spring through early fall seasons as well as the
coolest minimum air temperatures early summer through early fall. Mid-fall through
early winter the warmest average air was at the shoreline cliff, and the warmest average
ground temperature was in the forest near the shoreline. The coolest average air
temperatures mid-fall through early winter were in the open site and at the forest edge
near a branch pile; the coolest ground was in the ravine.
Table 8. Core and supplemental station temperatures (2001).
Temperature Station
Core Group
Late Spring
Early Summer Mid-Summer through Early Fall Mid-Fall through Early Winter
6-Jun to 20-Jun 21-Jun to 8-Jul
9-Jul to 24-Sep
25-Sep to 31-Dec
Air (C)
Min Max Av
Air (C)
Min Max Av
5.4 23.0 12.6
7.2 20.2 12.2
5.3 20.7 12.2
7.9 22.0 14.0
9.5 19.7 13.8
8.3 20.6 14.0
Air (C)
Min Max Av
Ground (C)
Min Max Av
Air (C)
Min Max Av
Ground (C)
Min Max Av
0.2 16.2 6.9
0.1 16.7 7.5
-0.7 16.4 7.2
2.0 14.7 8.8
0.9 13.8 9.4
3.6 14.3 8.8
a
Open site A (near garden)
Forest site A (near shoreline)
Forest site B (in forest)
Supplemental
6.4 26.9 15.1 11.5 20.8 15.2
8.0 26.0 15.0 12.1 15.7 14.0
7.2 24.8 15.0 11.3 16.6 14.2
a
Forest site C (cliff at shoreline)
Forest site D (ravine)
b
Forest site E (edge branch pile)
11.3 19.5 15.6 12.8 18.9 15.5
8.8 19.6 13.9 12.0 15.8 14.1
7.6 22.2 14.6 5.7 21.0 13.8
1.0 15.5 8.0 1.4 15.6 9.1
0.3 14.2 7.2 3.6 13.9 8.6
-0.2 15.2 6.9 -0.3 15.2 6.7
a
Core group ground data and all supplemental stations data start mid-summer, 9 August.
Ground column data is for a location above ground, but beneath a branch pile.
b
Tidal Channel Salinity
I took channel salinity data on 4 September 2001. I estimated a flow of 0.04 cfs in
the freshwater channel on that date. Salinity sample results are shown in Figure 14. The
lowest salinity measurements (0.05 to 0.07 ppt NaCl) were found in the furthest upstream
40 m of the channel. From 50 to 90 m, salinity increased from 0.15 to 1.50 ppt. At the
stream flow/tidal water confluence (distance 100 m) the salinity was 6.00 ppt. Salinity at
40
(a) Late Summer to Early Fall Mean Daily Air and Ground Temperatures
(Air temperatures are dashed lines, ground are solid lines)
Open site A, air
Open site A, ground
Forest site A, air
Forest site A, ground
Forest site B, air
Forest site B, ground
9-Aug
10-Aug
11-Aug
12-Aug
13-Aug
14-Aug
15-Aug
16-Aug
17-Aug
18-Aug
19-Aug
20-Aug
21-Aug
22-Aug
23-Aug
24-Aug
25-Aug
26-Aug
27-Aug
28-Aug
29-Aug
30-Aug
31-Aug
1-Sep
2-Sep
3-Sep
4-Sep
5-Sep
6-Sep
7-Sep
8-Sep
9-Sep
10-Sep
11-Sep
12-Sep
13-Sep
14-Sep
15-Sep
16-Sep
17-Sep
18-Sep
19-Sep
20-Sep
21-Sep
22-Sep
23-Sep
24-Sep
Temperature (C)
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-1
(b) Late Fall to Early Winter Mean Daily Air and Ground Temperatures
(Air temperatures are dashed lines, ground are solid lines)
Open site A, air
Open site A, ground
Forest site A, air
Forest site A, ground
Forest site B, air
Forest site B, ground
15-Nov
16-Nov
17-Nov
18-Nov
19-Nov
20-Nov
21-Nov
22-Nov
23-Nov
24-Nov
25-Nov
26-Nov
27-Nov
28-Nov
29-Nov
30-Nov
1-Dec
2-Dec
3-Dec
4-Dec
5-Dec
6-Dec
7-Dec
8-Dec
9-Dec
10-Dec
11-Dec
12-Dec
13-Dec
14-Dec
15-Dec
16-Dec
17-Dec
18-Dec
19-Dec
20-Dec
21-Dec
22-Dec
23-Dec
24-Dec
25-Dec
26-Dec
27-Dec
28-Dec
29-Dec
30-Dec
31-Dec
Temperature (C)
Date (2001)
Date (2001)
Figure 13. Mean daily temperatures at core sites showing reversal of air versus ground
temperatures between late summer to early fall (a), and late fall to early winter (b).
the last sample site (110 m) was of incoming tidal water; salinity at this site was 11.50
ppt. Results from substrate samples taken adjacent to the channel generally showed a
parallel trend, but had uniformly higher salinity than stream samples at the same distance.
41
12
11
In tidal channel
Near channel
10
35
6.
50
4
0
00
0.
05
05
07
05
0.
0.
0.
0.
47
Upstream
0.
2
6.
5.
6
09
NaCl (ppt)
8
.5
0.
05
0.
07
0.
15
0.
27
8
0.
3
1.
08
1.
50
Confluence
with incoming
tidal waters
0
0
10
20
30
40
50
60
70
80
90
100
110
Distance (m)
Figure 14. Salinity in the tidal channel and in sand bar or mudflat substrate within 2.5 m of
the channel. Measurements were taken 4 September 2001, during an incoming tide. Points
100 m and 110 m were of incoming tidal waters; all others were taken when tidal waters were
absent.
42
CHAPTER 5. NATURAL HISTORY AND BEHAVIOR RESULTS
This chapter describes some natural history, behavioral, and physiological data about
northern red-legged frogs using terrestrial habitat. I begin first with a brief overview of
telemetry data, and then utilize a composite of data types for remaining sections.
Telemetry
I radio-tracked frogs between 16 July and 29 December 2001. Figure 15 and
Appendix G Table G-1 provide overviews of the telemetry results. These data are briefly
described here, and used elsewhere throughout the remainder of the results.
0
424E61451B (2-May
to 17-Sep)
10
N
Both frogs migrated to hill on other side of cove
20
432C744D14 (15-Jun
to 1-Oct)
30
Study area boundary
40
Tidal Cove
50
5028025B2D (26-Aug
to 7-Nov)
60
70
Migratory
direction
Distance (m)
80
4250316221F (9 to
23-Sep)
90
OPENING
100
501C750D68 (11 to
16-Sep)
FOREST
110
120
130
501C6A3723 (22-Sep
to 14-Oct)
Shared use area
140
Tidal Cove
150
5006592732 (1 to 16Oct)
160
170
501C792B1E (24 to
30-Oct; off-site
telemetry to 29-Nov)
180
190
Tidal Channel
Ravine, south side of tidal channel
(outside of the study area)
200
501C400240 (2 to 12Nov; off-site telemetry
to 29-Dec)
210
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150 160 170 180 190
Distance (m)
Figure 15. Telemetered frogs home ranges and migratory patterns in 2001. Map includes data
from telemetry and other survey types.
I initiated telemetry with seven frogs captured in the open stratum (five from
opportunistic captures, and two from area-constrained searches). The remaining four
43
frog captures for telemetry were in the forest stratum (one from opportunistic capture,
one from an area-constrained search, and two from traps). Frog 432C744D14 had
telemetry gear during two intervals (hence 10 different frogs were telemetered during 11
intervals). I lost reception on one frog after the first day. In five cases (frogs
424E61451B, 5028025B2D, 432C744D14, 425031621F and 501C6A3723), I augmented
telemetry data through captures made before or after telemetry occurred. I also made
three observations of frogs carrying radio transmitters without the aid of telemetry. I
obtained a total of 79 frog observation days (counting one observation per frog per day
found) through telemetry.
I ended telemetry on individual frogs for three reasons: injuries associated with the
attachment belts, dropped or slipped transmitters, and loss of reception. In four cases (at
22, 36, 37 and 73 days of carrying the transmitter) I removed transmitters because the
frog developed dorsal sores
3 mm long beneath the attachment belt. I reattached a
transmitter to frog 432C744D14 40 days after removal, since its injury had healed. Three
frogs slipped transmitters 1 to 2 weeks after they had been put on. I had four occurrences
of lost reception that resulted in my losing the frog with the transmitter still attached. As
these transmitters had had some previous use, I was unable to precisely estimate
remaining battery life.
Temporal Extent of Terrestrial Use
In 2001 I recorded frogs in the study area from 21 April until 12 November, and at an
off-site terrestrial location until 29 December. In 2002, I found frogs from 29 April to 17
November. The earliest three frogs I observed in 2001 were females (the first two frogs
were observed but not caught and their SVL was estimated at between 65 and 70 mm, the
third frog was measured at 67 mm SVL). I did not observe the first male in 2001 until 7
May (SVL 55 mm). In 2002, the first frog was a 79 mm SVL, unmarked female. The
first frog I observed known to be a male was on 2 July 2002. However, I observed a ca.
45 mm SVL frog on 29 May 2002 of unknown gender making it possible that male frogs
were present before 2 July.
In fall 2001, between 8 and 15 October I caught six frogs without using telemetry or
traps. These frogs were 36, 56, 66, 71, 72, and 73 mm SVL indicating that adults and
juveniles were still present.
44
After 15 October 2001, I found only adult females (n = 4), and found them solely
through trapping and telemetry. I had initiated telemetry on two of these females prior to
15 October. One (5006572732) lost its transmitter between 16 to 19 October. I tracked
the second frog (5028025B2D) until 7 November (when I removed the transmitter due to
sores). During this period, this frog made only short moves; the longest move recorded
between 24 September and 7 November was 13 m over a 2-day period on 1 to 2
November (Appendix G Table G-1).
I initiated telemetry on the other two frogs after 15 October when each was caught in
a trap. Both made long-distance moves (e.g., 501792B1E moved an estimated 511 m,
and 501C400240 moved an estimated 297 m). One, 501C792B1E left the study area
between 26 and 27 October, and the second (501C400240) left during the interval 12 and
18 November. Both moved to terrestrial locations where at least one remained until 29
December 2001.
Migratory Patterns and Migratory Stop-Overs
Spring Movement Patterns
In the two weeks prior to the first northern red-legged frog sighting in 2001 (21
April), 50% of days had rain, the largest rainfall event was 8.6 mm, and the daily mean
was 2.0 mm. Thus, no storms brought heavy rainfall during this period, but conditions
were continuously either moist or wet. The mean air temperature for the 7 days prior to
21 April 2001 was 9.3 C (TESC weather station, Fig. 11). This was the highest 7-day
mean spring value recorded to date.
I captured the first frog in 2002 over 2 consecutive days (29 to 30 April), during
which time it traveled 26 m in a southerly direction (opposite to the dominant fall
movement direction I observed in 2001).
I obtained eight captures of six different frogs during the April to May 2001 interval.
Of these, one (424E61451B) later became telemetered and was observed at the study area
every month, May through September. A second frog (424D19136) represented three of
the eight April to May captures. Overall, it was observed at the study site five times from
7 May to 18 June. Of the remaining four frogs, three (424F2E3128, 432E53200E, and
45
432E56314B), were only captured once and the fourth was captured once in 2001 (19
May), but it had been previously captured and tagged 25 September 2000.
Small Frogs
In 2000 I saw no small frogs < 10 g. However in 2001 I observed five small frogs (<
10 g). These frogs were captured each once, on 15 July, 16 July, 28 July, 6 August and 8
October with respective masses of 9.0, 8.0, 6.0, 5.5 and 3.0 g. Additionally in 2002, I
found two frogs < 10 g; both were found on 30 June, and they had masses of 7 and 8 g.
Fall Movement Patterns
In early fall 2001 the ratio of newly tagged to total frogs caught increased from 50%
to 56% (Table 7). In mid- fall 2001, this ratio increased to 65% newly tagged frogs. In
addition, the CPUE for area-constrained surveys mid- fall was 50% greater than during
earlier seasons (Table 3).
I observed a diversity of patterns and timings of movements in the fall of 2001. For
example, while telemetered frog 5028025B2D stayed within the same vicinity until at
least 7 November (Appendix G Table G-1), frog 501C792B1E, a previously untagged
frog trapped 24 October, made a 49 m move on 26 to 27 October, and 105+ m move 30
to 31 October.
In fall some frogs moved when substantial rain interrupted summer dry conditions.
During 21 and 24 August 2001 53.9 mm of rain fell. Following this on 25 to 26 of
August, I captured eight frogs of which seven had not been previously tagged (a ratio of
newly captured to total frogs of 0.88). I also determined that three dead trapped frogs had
been caught on 21 August, which brought the ratio of new to total frogs caught to 0.91.
In contrast, the new to total frog ratio for 20 frogs caught 9 July to 20 August 2001 was
0.45.
The recapture and movement data from six untagged frogs caught 25 to 26 August
provides an indication of the diversity of movement patterns seen in the fall. Four frogs
were not recaptured. I relocated one frog on 30 September 2001, 31 m southwest of the
original capture location. I radio-tracked the sixth frog (5028025B2D) and found that it
remained in the study area through at least 7 November 2001.
46
For 2002, the data show a unique set of frogs during the dry 14 August to 6 September
interval that had all been located earlier in the summer. However, I began to find
untagged frogs a day after it had rained (8 September) and onwards. In addition to
finding frogs at this time, I found them in a group, and or using the same localized
habitat. After finding the first of these frogs on 8 September, I found a different frog in
the same 6.25 m2 subquadrat on 11 September 2002. I subsequently refound this second
frog within a 5-m distance on 18, 19 and 28 September. On 19 September a new frog
was present 5- m away, and on 28 September at least three more untagged frogs were
present within 5 m of each other. After 28 September, through fall of 2002 I no longer
found frogs at this location.
Telemetry data from two female frogs (501C792B1E, 501C400240) in fall indicated a
large directional movement. Both moved northeast to the opposite side of the tidal cove
to a southwest facing forested slope and nearby forested hilltop plateau (Figs. 15&16).
Frog 501C792B1E traveled northeasterly near the shoreline edge, and then was next
located on the opposite side of a 30 to 40- m wide portion of the cove. Frog 501C400240
followed a similar route: both frogs crossed the road where I found vehicle-killed frogs.
Cold Weather Migratory Stop-Overs
Figure 16 shows the forested location along the shoreline used by frog 501C400240
during a mid-fall, cold weather period. Between 5 and 12 November 2001, average daily
temperatures at the study site were cold (4.6 to 9.3 C) and this frog made only minor
moves (e.g., < 1.0 to 4.0 m). Figure 17 shows the temperature and rainfall patterns
during the 20 October to 20 November 2001 interval when this and a second frog
(501C792B1E) made only minor moves when mean daily temperatures across study site
core group stations were at or below 9.3 C. When temperatures warmed, which in both
cases was concurrent with large rainfall events (peak rainfall of 18 mm on 31 October,
and 61 mm on 14 November), these two frogs resumed making longer directional moves.
Home Ranges
I identified two types of home ranges: primary active season (“primary”), and late fall
to early winter (“winter”).
47
Early winter home range,
18 November to 29
December
Cold weather
stop-over, 5 to 12
November
65
60
Cold weather stop-over: frog 501C792B1E
Cold weather stop-over: frog 501C400240
Core sites daily mean air (C)
Core sites daily mean ground (C)
Cold weather stop-over zone est. below line (9.3 C)
Daily rainfall (mm)
55
50
45
40
35
30
B
A
25
C
D
Rainfall (mm)
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
20
15
10
20-Oct
21-Oct
22-Oct
23-Oct
24-Oct
25-Oct
26-Oct
27-Oct
28-Oct
29-Oct
30-Oct
31-Oct
1-Nov
2-Nov
3-Nov
4-Nov
5-Nov
6-Nov
7-Nov
8-Nov
9-Nov
10-Nov
11-Nov
12-Nov
13-Nov
14-Nov
15-Nov
16-Nov
17-Nov
18-Nov
19-Nov
20-Nov
Temperature (C)
Figure 16. Telemetered frog 501C400240 map of 2001 mid-fall cold weather migratory
stop-over, mid-fall possible migratory route, and mid-fall through early winter home range.
Base photo from Thurston County Geodata.
5
0
Date (2001)
Figure 17. Cold weather migratory stop-over temperature and rainfall conditions. Point A:
frog 501C792B1E moved 49 m since the previous day. As temperatures dropped and then
increased during the 4 days shown by A to B, the frog moved 0 to 2 m/day. Point B: between
this date and the next 24 hr the frog moved ca. 105 m. Point C: between this date and the
2
next 7 days frog 501C400240 made only minor moves within a 12.5 m area. Point D: frog
501C400240 was located ca. 297 m distant, where it remained at a late fall to early winter
home range until at least 29 December 2001.
48
Primary Home Range Size and Habitat
Frogs used diverse habitats within their primary home range. Female frog
424E61451B was located between 2 May and 17 September 2001 in both open and forest
strata, and in substrata ranging from tidal mudflats and forest/sword fern, to open/grass
and open/buttercup (Fig. 18). The home range of this frog was 11 by 62 m. Similarly,
female 432C744D14, observed from 15 June to 1 October, ranged over an area 18 by 71
m, and female 5028025B2D, observed 26 August to 7 November, ranged over an area 9
by 80 m. Locations of these largely non-overlapping ranges are shown in Figure 15.
120
2-May
N
125
4-Jun
23-Aug
Distance (m)
28-Jul start of telemetry
17-Sep
130
4-Sep end of telemetry
135
26-Aug
140
145
Forest/Sword Fern
Grass
Forest/Shoreline Cliff
Buttercup
5,6,13-Aug
19,20-Aug
Tidal Mudflats
30-Jul
150
70
80
90
100
110
120
130
Distance (m)
Figure 18. Spring through summer (2 May to 17 September 2001) home range and macrohabitat use by female telemetered frog 424E61451B. Distances are from the NW and SW
corners of the study area (see Fig. 3).
49
Movement within Primary Home Ranges
The predominant movement pattern that I identified within female home ranges was
that of short distances (Table 9). My observation frequencies for the three female frogs
were 0.09 to 0.27 days. Frogs relocated at points 0.2 to 69.1 m apart between
observations, and mean distances traveled between observations ranged from 8.4 m to
15.6 m. I estimated mean daily travel distances between 1.4 and 2.3 m. Similarly, for 12
observations where location data were taken on consecutive days for these three frogs the
mean distance moved was 1.6 m (range: 0.2 to 4.4 m; see Appendix G Table G-1).
Table 9. Distances moved by frogs within their home ranges (2001).
Home
Range
Type
Frog No.
Primary
Primary
Primary
Winter
424E61451B
432C744D14
5028025B2D
501C400240
Observation
Duration
Range of Dist Mean Dist
Return
Moved Mean Dist
Total No. of
Moved
Visit
between
Moved/
No. of Obserbetween Visits
a
b
Days vations Freq
(m)
Visits (m) Day c (m)
2-May to 17-Sep 139
15-Jun to 1-Oct
109
26-Aug to 7-Nov
74
18-Nov to 29-Dec
41
13
12
21
16
0.09
0.10
0.27
0.37
<1.0 to 38.0
<1.0 to 69.1
0.2 to 39.4
0.0 to 13.6
15.6
20.9
8.4
3.4
1.4
2.1
2.3
1.3
a
This is the number of observations minus one, divided by the total number of days in the observation period.
For this calculation all measurements such as <1.0 m were treated as =1.0 m.
c
This is calculated for comparative purposes only; the actual movement distance per day is not known.
b
Multi-year use of primary home ranges-- From 2 July to 6 September 2002, I made
13 opportunistic frog observations of five different frogs. Of these frogs, 2002 was the
second observation year for two, the third year for one, and, the first year for two. Thus,
three returning frogs revealed that at least some of the same frogs return to primary home
ranges. Figure 19 displays the locations found, by year, for each of the three frogs.
Winter home range-- I documented the off-site, winter home range used by frog
501C400240 from at least 18 November to 29 December 2001 (Fig. 16, Appendix G
Table G-1). The general pattern of use was of small, but frequent moves (Table 9). The
frog exclusively used forest habitat with complex shrub, wood, and dense leaf litter.
50
100
424D5D1C4A (31-Aug
2000)
110
OPENING
N
120
424D5D1C4A (8-Aug
2001)
130
424D5D1C4A (2-Jul
2002)
Distance (m)
140
150
432E710B2C (25-Jun,
16-Jul, 6-Aug 2001)
FOREST
160
432E710B2C (10-Aug, 6Sep 2002)
170
Tidal Cove
180
5028025B2D (26-Aug to
7-Nov 2001)
190
Tidal Channel
Upland ravine, south side
of tidal channel (off-site)
200
5028025B2D (22-Jul to
24-Sep 2002)
210
0
10
20
30
40
50
60
70
80
90
100
110
Distance (m)
Figure 19. Locations of three frogs found during summer 2002, that were previously found
in 2000 and/or 2001. The year 2000 datum is square, 2001 data are triangles, and 2002
data are circles. Distances are from NW and SW study area corners (see Fig. 3).
Northern Red-legged Frog Ethology and Natural History in Terrestrial
Habitat
Preliminary Ethology
I found terrestrial frogs were usually concealed (e.g., by remaining motionless, by
employing cryptic coloration, and by using cover), and jumped upon my approach
(typically within 0.5 m). Data from my observations of undisturbed frogs (typically
found through tele metry), from video footage of frogs, and from other study data are
organized into a preliminary characterization of terrestrial northern red- legged frog
ethology and natural history (Table 10).
This ethology encompasses: postural behaviors, variation in mo vements (including
distance and in-place movements, movement patterns, and home ranges), vocalization,
physiology, responses to predators, local habitat modification by frogs, and general
aspects of social structure. Table 10 provides an overview of the categories and included
behaviors, and Appendix H provides additional description for selected behaviors.
51
Table 10. Preliminary northern red-legged frog ethology and natural history in its terrestrial
habitat. (Postural, movement, physiology, and vocalization behaviors are described
in Appendix H. Most other listed behaviors are described within the results.)
Postural
Physiology
Sit
Crouch
Lay
Eye Retraction
Breathing (throat movement)
Cryptic Coloration
Warm Light
Cold Dark
Water Absorption
Evaporative Cooling (assumed)
Distance Movement
Hop
Walk
Dive
Climb
Predator/Danger Responses
Before, or Not Caught
Crypsis
Hop(s) and Crypsis
Use of Covered Habitat to Move Away
At/After Being Caught (human, minnow trap)
Expel Liquid from Vent
Vocalization
Vigorous Attempt to Jump
Move/Squeeze through Small Space
Climb
In Place Movement
Head Turn (or Upward, or Downward)
Prey-tracking
Other-tracking
Unknown
Head Nodding
With or Post Feeding Lunge
Other
Feeding Lunge
Successful
Not Successful
Unknown
Repositioning
Body Turn
Other Minor
(Flinches, Jerks, Slight Movements)
Habitat Modification
Crouch Depression/Pad
Vocalization
Distress Calls (when human caught)
Soft Cortling
Squeaky Scream
Male Breeding Call
Movement Patterns and Home Ranges
Primary, Long Seasons Home Range
Secondary, Winter Home Range
Migratory Stop-Over
Spring and Fall Migrations
Social Structure
Shared Important Resource Areas
Migratory Grouping
Other, Pairs
Video results and analysis-- I recorded nearly 11 hours of video tape. Table 11
provides an overview of the video data and analysis. The analysis showed frogs rarely
moved. Specifically, movement occurred a mean of 0.46% (range: 0.33 to 1.73%) of the
time; conversely, frogs were motionless 99.54% of the time (range: 98.27 to 99.67%).
All frogs spent a combined total of only 181 sec moving. During those 181 sec, I
observed 123 movement episodes (activities), comprised of 149 individual behaviors.
The mean length of any activity was 1.5 sec. Table 12 provides an analysis of the
52
Table 11. Red-legged frog video analysis overview. An activity is a movement episode. Each activity may have one or
more individual behaviors.
Time
424E61451B
Seconds
Time
Mean
Activity
Length
Start and
ObserEnd
vation
c
Times
Length
hr:min:sec hr:min:sec
Descriptionb
Movement
Behaviors
Date
Season
Activities
Frog No.
a
no. no.
no.
%
sec
13-Aug-01
Mid/Late
Summer
26-Aug-01
Early Fall
17:27:00 1:04:24
18:31:24 3864 sec
11
17
16
0.41
1.5
15:47:00 0:35:36
16:22:36 2136 sec
5
6
7
0.33
1.4
424E61451B
4-Sep-01
Early Fall
09:20:36 0:45:08
10:27:11 2708 sec
12
17
15
0.55
1.3
501C750D68
13-Sep-01
Early Fall
12:58:00 3:05:58
17:12:03 11158 sec
35
41
65
0.58
1.9
501C750D68
14-Sep-01
Early Fall
13:50:03 4:42:10
18:55:30 16930 sec
41
47
57
0.34
1.4
425031621F
17-Sep-01
Early Fall
19:04:00 0:32:02
19:36:02 1922 sec
5
6
7
0.36
1.4
Frog in sit posture at dusk in dry forest edge 0.5 m from
cleared edge of open habitat. Air 13.4 C. Ground 14.0 C.
Frog does not pursue flying insect.
424E56143B
23-Sep-01
Early Fall
15:00:00 0:13:31
15:13:31 811 sec
14
15
14
1.73
1.0
Frog is elevated 33 cm on wood in sun, in flower garden.
Air 19.4 C. Ground 13.7 C.
7 unsuccessful lunges at mosquito. Dive out of video.
0.46
1.5
424E61451B
Totals:
10:58:49
39529 sec
123 149 181
Mean values:
a
All frogs with the exception of 424E56143B were found through telemetry.
b
Temperatures are from closest installed air and ground thermographs.
c
Includes additional time when video was not running; the observation length is correct.
53
Frog on small cave-like ledge on cliff face, overlooking cove. Video from above. Dry sunny condition.
Air 17.6 C. Ground 16.5 C. Successful feeding.
Frog in crouch posture on moist forest floor. Air 18.8 C.
Ground 14.0 C. Includes head turn toward ant: frog
does not pursue ant.
Frog in crouch posture, elevated 20 cm on moist, moss
covered log. Air 14.2 C. Ground 14.0 C. Video includes
repositionings, head turns, and a hop.
Frog in crouch posture, grass/forbs habitat. Dry condition. Mean air 19.2 C. Mean ground 15.3 C. Video includes a head turn, feeding lunge, head nodding sequence.
Frog in sit posture, in dry grass/forbs, 5 m from 13-Aug-02
location. Mean air 19.2 C. Mean ground 16.1 C. Includes
feeding, and non-feeding beetle and spider interactions.
Table 12. Video analysis of number of frog movement behaviors and seconds of movement activitya. Movement
types are described in Appendix H.
Frog no., Date
Dist. Movement
Physiology
Total
Eye
Retraction
Other
Other
Minor
With
Lunge
Body
Turn
Not
Successful
Repositioning
0
0
0
0
0
0
0
0
0
0
5
3
1
5
1
1
1
1
0
0
0
0
0
0
2
1
7
5
17
16
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
0
0
0
0
1
3
0
0
1
1
2
1
6
7
1
1
0
0
0
0
0
0
1
1
4
4
0
0
0
0
0
0
0
0
2
3
0
0
3
3
6
3
17
15
0
0
1
5
0
0
1
1
0
0
3
5
1
1
0
0
1
4
1
0
2
2
3
6
19
22
9
19
41
65
0
0
0
0
0
0
0
0
1
1
7
7
1
1
0
0
1
0
1
0
4
11
2
2
14
15
16
20
47
57
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
3
3
2
4
6
7
0
0
1
1
1
1
0
0
0
0
0
0
0
0
7
7
0
0
0
0
2
2
2
1
2
2
0
0
15
14
1
1
2
6
1
1
1
1
3
3
20
20
3
7
8
8
3
5
3
0
11
21
7
9
44
47
42
52
149
181
Preytracking
Othertracking
424E61451B, 13-Aug-01
no. of behaviors
sec/activity
424E61451B, 28-Aug-01
no. of behaviors
sec/activity
424E61451B, 4-Sep-01
no. of behaviors
sec/activity
501C750D68, 13-Sep-01
no. of behaviors
sec/activity
501C750D68, 14-Sep-01
no. of behaviors
sec/activity
425031621F, 17-Sep-01
no. of behaviors
sec/activity
424E56143B, 23-Sep-01
no. of behaviors
sec/activity
Grand Totals
no. of behaviors
sec/activity
Head
Nodding
Successful
Walk Dive
Feeding
Lunge
Unknown
Hop
In-Place Movement
Head
Turn/Up/Down
a
Where an activity includes more than one behavior, seconds are allocated to what appeared to be the primary behavior.
54
number of each type of movement observed, and the number of seconds involved in each
movement. In-place movements were the most frequent behaviors (103, 69%) and
comprised the greatest fraction of time movement behaviors occurred (121 sec, 67%).
Within this category, other minor movements (e.g., quick jerks, or flinches of a portion of
the frog) were the behavioral category most frequently scored (44) and took up the most
time (47 sec). Other minor movements accounted for 30% of all movements.
The next largest number of observations of a behavior for the in-place movement
category was head turn (or upward or downward). This behavior was involved in prey
tracking once (the prey was subsequently taken); three times it involved observations of
insects that the frogs did not attempt to take as prey; and 20 times I could not determine
the behavior purpose.
Four video sessions included a feeding lunge or lunges; three of these included
successful capture of prey. Based on this limited sample, the frogs had an insect capture
rate of one per 3.7 hr. In one case, the prey was a ca. 8 mm flying insect, another was a
large, winged insect. Seven unsuccessful lunges by one frog were taken towards a
mosquito.
Feeding included up to five associated behaviors. For example one feeding episode
by frog #501C750D68 on 13 November 2001 included four such behaviors:
13:25:19
13:25:35
13:25:40
< 1 second
duration
<1 second
duration
4 seconds
duration
13:29:35 1 second
duration
Head turn (prey
tracking)
Feeding lunge
Head nodding
Repositioning
Quick movement of frog’s head and
uppermost body to right.
Frog propels forward using hind legs
(exposing telemetry gear and legs), while
head is thrust forward under a leaf and into
grass. Frog retracts back to starting location
using forelegs to reposition.
Head moves up and down quickly, ca. 6X.
Left fore foot moves, then upper torso and
head move, followed by movement of all
legs; frog appears to now be closer to the
ground.
All three successful feeding lunges included head nodding. Not included in the above
example, but present in both other successful feeding lunges was eye retraction. On 14
55
September 2001 frog #501C750D68 incorporated head nodding and eye retraction into
the feeding lunge:
14:06:36
1 second
duration
Feeding lunge;
head nodding;
eye retraction
Frog extends with a forward/upward lunge ca.
70 mm and captures insect in its mouth. This
movement is hind leg propelled, which (with
feet appearing to remain planted on the
ground) act as springs to thrust the frog
upward and then back down again. As the frog
moves back down, its head moves quickly up
and down 5X; concurrently its eyes close and
open.
The movement category with the second largest number of occurrences was
physiology. In this category, the eye retraction behavior was observed 42 times (28.2%
of all observed behaviors) and was the primary behavior activity for 52 sec (28.7% of all
movement seconds). Eye retraction occurred by itself, as well as with the feeding lunge,
head nodding, head turn and upward and downward movement, repositioning, body turn,
other minor motions, hop, and walk.
Distance movement (i.e., movements where the frog did not return to its original
location) was taped only four times, with a total of 8 sec of movement. The same frog
performed two distance movements; the first was a walk, followed ca. 2 min later by a
dive from wood the frog was on. This movement sequence was as follows (distance
component is bolded):
15:11:38 1 second
duration
15:11:48 1 second
duration
Body turn
15:13:28 <1 second
duration
15:13:31 <1 second
duration
Repositioning
Body turn/walk
Dive
Frog turns body by moving feet and torso 45
degrees.
Frog turns further and walks 10 cm to edge of
wood ending in a lay position with front feet
and head perched over edge of wood (elevated
33 cm above ground).
Front legs and head drop down 3 – 5 mm.
Frog propels out and down from wood and
moves out of video field of view.
The second frog for which a distance movement was scored hopped from downed
wood and the third frog walked. Distance movements by the three frogs caused them to
56
move out of the video, however searches within 30 min to 8 hr revealed each frog to still
be present within 1 m of the observation location in all cases.
Video Case Study
Frog 501C750D68 was observed between 11 and 16 September 2001 fo r nearly 8 hr
(7 hr 48 min 08 sec) over two days by video, and through additional non-video
observations. I use the data for this frog to detail an individual frog’s behavior, and to
provide greater context for the video data.
This frog moved 122 sec out of 7.8 hr of video observation, and was motionless
99.6% of the time (Fig. 20). During the 122 sec of movement she exhibited 88 individual
behaviors, including two successful feeding lunges (Fig. 21).
Spatial locations used by this frog, daily temperature information, and a chronology of
observations are presented in Figure 22. Overall, the frog stayed within an area ca. 11 m
long by 3 m wide. The habitat included an opening with grass and forbs, partially shaded
by tree canopy, and remnant patches of na tive trees and shrubs. On most days, she was
observed at a new location. The frog was observed in open habitat with two exceptions,
when she was in remnant edge vegetation, at an old-growth cedar log. On 12 September,
the frog hopped to the base of this log when I accidentally disturbed her, and through
telemetry I found that she spent the night and morning between 13 and 14 September
under the log. On 14 September, the frog stayed within 20 cm of its daytime location
into the night, and was visible by flashlight under low cover at 2215. At 0700 the next
morning, she was still within 25 cm of the previous day’s location in a dense patch of
grass under 100% cover. She stayed within or at the margins of this dense grass at least
until the last sighting at 1024 on 16 September.
57
Frog still
Frog moving
122 seconds of movement out of
28,088 seconds (7.8 hours) of video
observation.
Frog still 99.6% of observation
period.
Figure 20. Movement rate for frog 501C750D68 (13 to 14 September 2001).
4%
Clockwise from Top
11%
32%
Walk (n=1, sec=5)
2%
3%
11%
7%
Head turn/Up/Down
(n=12, sec=14)
Feeding lunge (n=2,
sec=2, all successful)
Head nodding (n=4,
sec=4)
Repositioning (n=6,
sec=13)
Body turn (n=5, sec=8)
Other minor (n=33,
sec=37)
Eye retraction (n=25,
sec=39)
Observation length: 7.8 hours (28,088 sec)
x
Movement behaviors: n=88
30%
Figure 21. Proportion of each type of behavior in 122 total seconds of movement for
frog 501C750D68 (13 to 14 September 2001).
58
Temperatures (C) a
Remnant native
trees, shrubs,
downed wood
Grass/forbs
11-Sep
13 to 14-Sep
(night refuge
under log)
12-Sep (arrow
shows escape
route)
13-Sep, video
Remnant
native
trees,
shrubs,
downed
wood
14-Sep, video
15 to 16-Sep
Frog location.
Scale: 1 sq = 1 sq m.
Date
Type
11-Sep Day low
Day high
Observ.
12-Sep Day low
Day high
Observ.
13-Sep Day low
Day high
Observ.
(video)
Observ.
Observ.
14-Sep Day low
Day high
Observ.
Observ.
(video)
Observ.
15-Sep Day low
Day high
Observ.
Observ.
16-Sep Day low
Day high
Observ.
Observ.
Time
0742
1642
1916
0742
1642
1118
0742
1642
1231
1542
1854
2000
0742
1642
1004
1312
1842
2215
0742
1642
1110
1920
0742
1742
0800
1025
Air
9.0
19.4
17.5
9.2
20.1
16.3
9.9
20.2
17.5
19.4
19.4
17.8
11.0
20.1
13.7
17.5
19.1
15.9
10.7
20.1
14.4
18.4
11.8
14.9
11.8
12.4
Grd
13.0
16.6
16.2
12.9
16.8
13.2
13.3
17.1
13.8
14.9
16.9
16.6
13.9
17.2
13.9
14.2
17.1
16.1
13.9
17.4
13.9
17.2
13.9
14.7
14.1
13.9
11-Sep. I found the frog at dusk (1916) in dry grass/forbs. The frog was very wet, i.e., it obtained moisture
elsewhere. The most recent rain was 8 days prior. SVL: 71 mm; weight: 34.5 g; gender female. This frog
was a new catch for the study area making it likely that it had not been at the study site through the summer.
I inserted a PIT tag and attached a telemetry transmitter.
12-Sep. I relocated the frog at 1118 within 0.25 m of its 11 September catch location. I saw the transmitter
under 20% grass cover and thought it had come off the frog. However, upon reaching for it, I found it was still
on; the frog made two hops, to the base of old growth cedar log with sword ferns.
13-Sep. 1231: I found the frog within 2 m of the 12 September location on on dry leaf litter, under 20% cover
from herbaceous plants, 65% canopy cover. I made video observations between 1258 and 1712. The frog
remained in this location until 1712 when based on the video tape it walked out of view.
1854: I located the frog 15 cm from its earlier location.
2000 (dark): frog had moved under an old growth, downed piece of a cedar log.
14-Sep. 0720, 0840,1004: the frog remained under the log.
1312: frog was visible with 10% cover from grass, 73% canopy cover. I video taped from 1350 to 1855.
2019 and 2215 (dark): the frog was at or within 20 cm of its daytime location.
15-Sep. 0700: I found the frog 0.25 m from the prior day's location. It was in a 0.25 m2 grass/forbs patch that
provided 100% cover. Canopy cover was 63%. This partially open habitat was saturated with dew. I made
additional observations at: 0720, 0910, 1110, 1310, 1511, 1711, 1920 (dusk). In all observations the frog
remained under cover, within 0 to 20 cm of its 0700 location. It was likely that the frog was able to actively
observe and feed within the covered location, but it was not visible and thus could not be video taped.
16-Sep. 0800: I located the frog within 0 to 5 cm of yesterday's dusk location. Dew was on the vegetation.
1024: last time I saw the frog; I found its transmitter within 0.25 m of this location on 1-Oct-01.
a
Temperatures are from installed thermographs within 20 m of frog location. Ground temperature times are
1 - 2 hours after time shown for daily high and low.
Figure 22. Case study for frog 501C750D68, 11 to 16 September 2001.
59
Behavior Patterns in Response to Seasonal Environmental Variables of
Temperature and Moisture
As moisture and temperature conditions varied by season, I observed frog behavior
patterns as environmental variables changed. In early summer, the ground began to dry,
and I found frogs in remnant moist surface locations. As summer temperatures warmed
and the period of drought increased, the forest floor became dry, with only some downed
wood, vegetation, and adjacent tidal mudflats remaining moist. However, during
otherwise dry conditions, dew and guttation moisture were present on grass/forbs
vegetation during early morning in the open habitat stratum. By mid-October moist
conditions were again becoming nearly ubiquitous at the study site (Fig. 12). In this
section I present observations and data that allow an inference of frog behaviors related to
temperature and moisture.
Summer to Early Fall Drought Conditions and Frog Use of Moist Open Habitat
Near the Forest Edge
On several occasions, I observed frogs in the open 0.3 to 2.8 m from the forest edge
when dew and/or guttation moisture was present. For example, at 0745 hr on 9 July 2001
(11 days since the last rain), I encountered a frog opportunistically in a location as
described above. However, during the day’s area-constrained searches conducted
between 0812 and 1116, no additional frogs were found.
I made similar observations on 14, 17 and 20 July 2001. One was for telemetered frog
432C744D14, located at 1300 on 16 July 2001, under an old branch pile (50 cm high, 5.2
m long and 2.2 m wide) inside the forest edge. At 0630 the next morning I observed this
frog 2.8 m out from the forest edge in 11 cm high grass, 8.3 m from its previous day’s
location.
Summer to Early Fall Drought Conditions and Observations of Very Wet Frogs
During the extended drought, I found very wet frogs in dry microhabitats within
forested and open habitats. These frogs were water saturated such that when picked up,
copious water flowed from them. I made the first observation of a very wet frog on 8
August 2001. I found this frog near the top of a small cliff along the shoreline. I had
bumped an overhanging dry mass of live and dead sword fern leaves and the wet frog
catapulted out of the leaf mass. I re-encountered this frog at dusk (2030) on 13 August
60
2001, this time down on the moist tidal mudflat near the cliff base. Other than the
mudflats (mudflat salinity 20 m upstream was 6.35 ppt), no obvious sources of moisture
were evident nearby. I also found telemetered frog 432C744D14 “very wet” on 20
August 2001, covered by dry leaves, in the ravine 4 to 5 m from the tidal stream.
Telemetered frog 501C750D68 (earlier described in the video case study) was very
wet in a dry, visible location at dusk (1916) on 11 September. On both 13 and 14
September it was observed through video in dry, warm conditions, actively feeding.
On 10 September 2001 frog 425031621F emerged wet from an environs of moist
moss, as I disturbed the site while trying to locate the frog by telemetry. I relocated this
frog on 17 September 2001, 7 m from the prior noted location in a dry, openly visible
location at the forest edge.
Summer to Early Fall Drought Conditions and Frog Use of Moist Garden Soils,
Crouch Position and Crouch Depressions
During hot droughty conditions in the summer of 2002, I observed frog 5028025B2D
(23 July and 18 August; see Fig. 23) and frog 501C6F1873 (14 August) to be visibly
moist, while crouched on sandy loam soils. The locations were within 10 m of the forest
edge, in a flower garden that I kept watered.
On three occasions in 2002, I observed cleared, slight depressions the shape of the
frog’s ventral side, in locations where I
had been observing a frog in the crouch
position. At one of these sites (frog
5028025B2D, 23 July, Fig. 23), within
30 min of the frog’s arrival to the
location, I observed the hind legs of the
frog moving laterally outward and then
Figure 23. Frog 5028025B2D visibly
moist while in a deep crouch position
on moist garden soil on a hot summer
day (23 July 2002). Air 22.6 C, ground
19.7 C.
back to the frog’s torso, motions that
may have been clearing debris. In all
three observations, the depressions
lacked the small soil clumps or other
debris found immediately outside the
depression.
61
Observed Pattern of Home Ranges Included the Tidal Channel
All three primary home ranges included one or more locations along the tidal channel
(Fig. 15). Two frogs (424E61451B, 432C744D14) telemetered during dry summer
conditions showed the same pattern of moving to the channel vicinity at the end of July
and remaining until at least 20 August. Following the 21 August peak summer rainfall,
both frogs moved from the channel vicinity.
Shared Resource Area
The three identified primary home ranges were largely non-overlapping, but five of
nine telemetered frogs were found at least once in an open stratum location ca. 5 by 15 m
(Fig. 15). For example, on 17 September 2001, two previously telemetered frogs were
found within this area, and another two previously telemetered frogs were located within
10 m of this site. Other frogs, including the aforenoted group of migratory frogs from fall
2002, used this location as well. This “shared resource area” is a linear depression
vegetated by creeping buttercup (Ranunculus repens) and grass (Gramineae sp.), partially
shaded by remnant mature red alder and western red cedar trees. Roughly 0.5 ha of open
and forest habitat drain to this location. Other potential moisture sources include a
nearby septic mound, and native moss mulching of shrubs along the depression margin.
Seasonally, Frogs More Observable After Rain
Early summer through early fall, I found frogs more readily observable after rainfall.
The 3-day antecedent rainfall value was a useful predictor during this interval for finding
frogs (Table 13). Fourteen area-constrained surveys were done between 24 June and 29
September 2001. For seven of these surveys, the 3-day antecedent rainfall was 0.00 mm.
Of these seven surveys, only two had frog observations. In contrast, frogs were found
during all surveys with some level of 3-day antecedent rainfall. The greatest numbers of
frogs were found when rainfall was greater than 3.0 mm.
Table 13. Area-constrained survey number of frog observations and 3-day antecedent
rainfall, early summer through early fall.
3-Day
Total No.
No. of
% of
Total No. Range of
Antecedent
of
% of Surveys Surveys
Frogs
Frog No.
Rainfall (mm) Surveys Surveys w/Frogs w/Frogs Observed Observed
0.0
>0.0 to 3.0
>3.0
Totals:
7
4
3
14
50
29
21
2
4
3
29
100
100
62
2
6
10
18
0 to 1
1 to 2
3 to 4
CPUE (Mean
No. Frogs
Observed/
Survey)
0.3
1.4
3.3
Early Fall Frog Use of Moist Open Habitat
In early fall while the forest remained dry, portions of the open grass/forbs habitat was
shaded all day due to the increasingly lower sun angle. Such habitat became very moist
through cumulative days of dew and guttation moisture. During the 24 September 2001
area-constrained survey, tidal mudflats, and down wood were the only areas with
moisture in the forest quadrats. However in the open stratum, one surveyed quadrat in
the shaded grass/forbs habitat had moisture evident over 90% of the area. This quadrat
had the greatest percent of moisture of the six open habitat quadrats surveyed, and was
the only location during the day’s area-constrained surveys where a frog was found. I
opportunistically found a second frog in an adjacent similar quadrat within 4 m of the
first frog.
Mid-Fall Coloration Change
The cryptic coloration of red- legged frogs changed in mid-fall. Throughout the dry
summer through early fall 1 , frog coloration closely resembled dry, big- leaf maple leaflitter. By November, this coloration had darkened and now closely resembled the darker
brown of water saturated big- leaf maple leaves. This color change can occur rapidly, as I
have two observations where frogs I captured changed from the dark to the light
coloration within 30 min and 1 hr.
Mid-Fall to Early Winter Cold Temperatures Limit Activity and Frogs Use
Complex Habitat
Colder temperatures mid- fall through early winter were associated with altered
patterns of frog activity. The movement interruptions at temperatures below 9.3 C (Fig.
17) are an example. Figure 24 shows sword fern/maple leaves habitat used by frog
501C400240 during November 2001. This complex habitat provided an array of microhabitats, including a burrow location utilized at cold temperatures (< 7 C air and ground);
concealed open space between the extended sword fern skirt and the ground used at a
moderate temperature (9 C air and ground); and a visible, elevated location utilized when
air and ground temperatures were 12 and 11 C, respectively. For all frogs for which a
location could be precisely identified between 16 October and 29 December, I found
them exclusively in such complex native forest vegetation. This complexity was lacking
in grass/forbs and manicured shrub environments of the open stratum.
63
Visible, elevated
Cold weather
burrow
Open space between
vegetation and ground
7-Nov-2001 (1105). Cold weather burrow. Air and ground 7 C. Frog located in a 10 cm tall
chamber at the base of a sword fern. The location was vertically under a 15 cm high, leaf and
sword fern frond matrix, and horizontally behind 25 cm of sword fern fronds and maple leaves. Upon
disturbance, the frog traveled below the vegetation 0.4 m, where it was refound through telemetry.
11-Nov-2001 (0950). Above ground opening under dense cover. Air and ground 9 C. Frog
in opening beneath roof of sword fern fronds, Oregon grape (Berberis nervosa ), and maple leaves.
This location is connected to the cold weather burrow through at least one opening. Frog is probably
able to feed within this opening.
12-Nov-2001 (1417). Elevated on sword fern frond, visible. Air 12 C, ground 11 C. Frog
presumed able to feed in this open location.
Figure 24. Mid-fall structural locations within a sword fern and maple leaf complex that
were used at differing temperatures by female frog 501C400240.
Frog Visibility, Structural Location, and Temperature
Figure 25 shows six categories of frog visibility and structural location, relative to air
and ground temperatures. Frogs were found in sub-surface locations during cold
temperatures (ground and air 2.0 to 9.0 C). Sub-surface locations in which I found frogs
included: a 2.5 cm high crevice in soils along a slope (n = 1); small mammal excavations
or openings below or within sword fern boles (n = 2); location under dense twig and leaf
litter accumulations at the base of a log (n = 1); and an opening created by two
1
An exception was a wet, dark colored frog fround 0642 hr on 10 August 2002.
64
26
Visible, elevated 10 - 30 cm (n = 5)
Visible, on ground <11% cover (n = 6)
Visible, on ground 11 - 80% cover (n = 5)
Not visible, dense grass/forb habitat, >80% cover (n = 3)
Not visible, between live vegetation and ground, 100% cover (n = 5)
Not visible, sub-surface below duff, or duff and soil ( n = 14)
Ground (C)
24
22
20
18
16
14
n = 2 (for not
Ground warmer
visible, subsurface)
Figure __. Frog
location and temperature. DRAFT: ADD 2002
DATA.
than visibility,
air
12
10
Ground cooler
than air
8
6
n=2
n = 3 (for not
visible, subsurface)
4
2
0
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Air (C)
Figure 25. Frog visibility, structural location, and temperature. Temperatures were taken
at the frog site.
developing chanterelle (Cantharellus sp.) fruiting bodies (mushrooms) that were pushing
a dense twig, duff and leaf layer upward as they developed below the ground.
At air and ground temperatures
10 C air and ground, frogs were found either
elevated on wood or vegetation, visible on the ground with varying amounts of cover, or
concealed beneath leaf litter. Below 10 C air and ground, frogs were found either under
100% nearspace cover (above ground but beneath live vegetation), or in the sub-surface
locations I have described previously. An exception to this was on 21 December 2001; at
air and ground temperatures of 7 C, I observed frog 501C400240 with 70% of its body
concealed by leaves, but its head and one foreleg were visible. Below air and ground
temperatures of 7 C, frogs were exclusively found sub-surface.
Summary of Terrestrial Behavior
Figure 26 (a to d) uses data from area-constrained searches, telemetry, and trapping to
provide a visual summary of the locations of terrestrial frog observations at the study area
by season in 2001. During spring and early summer (Fig. 26a), frogs were found in a
dispersed pattern throughout the study area during area-constrained surveys. Telemetry
had not yet started, and limited trapping provided no data.
65
20
20
Study Area Boundary
40
Distance (m)
60
80
80
FOREST
Tidal Cove
100
100
OPENING
120
120
140
140
160
160
180
180
Tidal Channel
200
0
20
40
200
60
80
100
120
140
160
180
0
(c) Early Fall
22-Aug to 24-Sep
0
20
60
20
40
60
80
100
120
140
160
180
(d) Mid-Fall
25-Sep to 27-Nov
0
Area-const. survey
Trap
Telemetry 424E61451B
Telemetry 425031621F
Telemetry 501C750D68
Telemetry 5028025B2D
40
Distance (m)
Area-const. survey
Trap
Telemetry 424E61451B
Telemetry 432C744D14
40
Area-const. survey
60
N
(b) Mid-through Late Summer
9-Jul to 21-Aug
0
(a) Spring and Early Summer
4-Jun to 8-Jul
0
N
20
Area-const. survey
40
Trap
60
Telemetry 432C744D14
80
Telemetry 5006572732
100
100
Telemetry 501C400240
120
120
140
140
160
160
180
180
80
200
200
0
20
40
60
80
100
120
140
160
180
0
Distance (m)
20
40
60
80
100
120
140
160
180
Distance (m)
Figure 26. Seasonal frog use of the study area in 2001.
In mid-to- late summer (Fig. 26b), temperature and moisture conditions were typically
warm and dry. During area-constrained surveys I only found frogs in the southern-half of
the study area. Several of the area-constrained survey frogs were found along the edge
between the forest and open strata. The two telemetered frogs both traveled to far ends of
their primary home ranges to locations near the tidal channel. Both remained near the
channel until at least 20 August 2001. The largest rain of the summer began August 21.
On this day three untagged frogs were caught in traps near the western edge of the stud y
area.
During early fall (Fig. 26c), both telemetered frogs that had been along the tidal
channel moved away from the channel (one was no longer telemetered and therefore is
not shown). Except for one frog caught in a trap in the northern portion of the site, all
66
frogs were found in the southern half of the site. The forest and open edge, and the open
stratum location with accumulated dew were where most frogs were found. Telemetry
data shows a concise use-pattern of relatively small distances for three frogs, and one
frog was found to be using immediately adjacent sides of the tidal channel.
Mid-fall (Fig. 26d) revealed a broad spatial use of the study area by frogs. During
area-constrained searches, I found most frogs in the southern-half of the stud y area.
However three frogs1 found during area-constrained searches in the northwest corner of
the study area and frogs caught in traps in the northeast portion of the study area
indicated a broader spatial use of the study area, and movement pattern. One telemetered
frog was found along the tidal channel and another maintained a primary home range in
the forest near the channel until at least 7 November 2001. Using telemetry, two frogs
were tracked making longer movements along the tidal cove and both were subsequently
observed northeast of the study area across the tidal cove. Both interrupted movement
during cold weather before crossing to the other side of the cove.
1
Two were caught and one escaped. Of the two caught, one had not been previously caught and tagged,
and the other had been tagged 4 days prior.
67
CHAPTER 6. DEMOGRAPHIC, ENVIRONMENTAL
CONDITIONS, AND NATURAL HISTORY AND BEHAVIOR
DISCUSSION
In this discussion, I consider elements of observed terrestrial northern red- legged frog
use including demographics, and my research hypothesis regarding a possible preference
for human created terrestrial openings. I also provide a synthesis of moisture and
temperature data and frog behaviors.
Demographics
Population Estimate
Terrestrial northern red- legged frogs were difficult to census with a high degree of
certainty. Marking with unique PIT tags was useful for providing a minimum number of
known, unique frogs. PIT tag data analysis indicated seasonal ratios of newly tagged
frogs were found at a rate of 50% or higher throughout the study (Table 7), providing
evidence that the number of uniquely tagged frogs was a low estimate. The study
methodology of utilizing stratified random area-constrained search-day catch data along
with PIT tagged individual frogs, with the Schnabel population estimation technique, was
most useful for population enumeration.
Some frogs clearly stayed within an active season home range at the study area, but
with the exception of the time intervals of warm droughty conditions, I could not rule out
that there may have been movement not associated with a home range throughout much
of the active season. Small frogs (5 to 9 g), undoubtedly young of the year, were first
found at the study area at least 2 months after the first adults were observed. In addition,
my results and observations indicated migratory movement to overwintering habitat
might extend from mid-August into November. I also cannot rule out that this migratory
period could extend later. An implication of this for census work is that closedpopulation requirements of estimation methods such as the Schnabel population method
will be difficult to meet. However, focusing on the expected non- migratory interval
before mid-August should provide the best approach.
68
Mortality is likely to occur as well. Licht (1974) reported the requirement for no
mortality was unable to be met in his Schnabel estimates for R. aurora aurora and R.
pretiosa pretiosa in British Columbia. However, he compared the Schnabel estimates
with results from the Lincoln Index and the Schumacher method and reported finding
“nearly identical results” for metamorph life history estimates, lending confidence to the
methodology.
Traps were useful, but not effective at catching many frogs. I suspect some frogs
were caught and then escaped; on one occasion I put a robust mid-sized frog in a trap in
the evening and it was gone by morning. An improved trap design may have been able to
prevent this from occurring. In addition, setting a drift fence with traps along an
expected migratory or movement route may be more successful than random placement
of arrays. For example, the one array in my study that had the most catches appeared to
be in a migratory pathway.
Frog Growth Data
An important finding related to the three size measurements (SVL, shank length and
mass) was evidence that the primary period of frog growth was during spring through
mid- fall. Licht (1974) found postbreeding female northern red- legged frogs did not
develop eggs before July and therefore observed that food eaten before July was
apparently not used for egg production. During July on, food eaten was assumed to
include utilization for egg production. He also found larger females tended to have more
eggs. Thus the overall size and fecundity of female frogs may be dependent upon habitat
conditions conducive to feeding and growth.
Frog Ages
Frog ages were difficult to discern. Based on size, the very smallest frogs (e.g., with
masses in the 3 to 9 g range) were probably young of the year. The third year finding of
male 425D5D1C4A, (age minimum 2+, mass 15 g), indicates that low-mass frogs can be
at least 2 years old. Snout- vent length data for female frogs with two data years showed a
pattern indicating roughly three size groups, which may reflect three age classes. These
group are: 50 to 60 mm, 60 to 70 mm, and > 70 mm. For example, two females had
measurements of 51 and 52 mm (respectively) their first capture year. The second
69
capture year, they were 66 and 61 mm. A different two females had SVL measurements
of 60 to 63 mm, and 65 to 67 mm (respectively) the first year caught. During their
second year, they measured 73 to 74 mm, and 74 to 78 mm, respectively.
Mortality Factors
Both natural and human caused sources of mortality may exist at the study site, but
with the exception of trapping mortality none were evident. The largely motionless
behavior and cryptic coloration of the northern red- legged frogs may be a successful
strategy for preventing detection, which likely makes them less vulnerable to predation.
However I was unable to adequately assess whether predation was a key factor within
active season habitat (i.e., on the study site) as the fate of most frogs that were captured
only once was unknown.
Periods of terrestrial movement, especially longer movements such as occur between
breeding, active season, and overwintering habitats, may be significant interva ls during
the terrestrial life history during which northern red- legged frogs are vulnerable. These
major moves tend to occur during rainfall events and at night (e.g., Nussbaum et al. 1983;
Licht 1969; and my observations), both which likely provide some protection. The cover
of darkness and a rainfall screen may interfere with the visual field of potential predators;
moreover, rainfall could possibly reduce scent-tracking abilities of some mammalian
predators.
In developed areas, frog movement across roads is clearly a direct source of mortality
to northern red- legged frogs and other amphibians (this thesis; Beasley 2002; Lamoureux
& Madison 1999). This is an important issue that should be hypothesized as being one of
a major group of threats to northern red- legged frog populations in areas of development.
Analysis of Hypothesis Regarding Attraction to Human-Created Openings
Telemetry was essential for learning about patterns of use of the study area and
environs by the frogs. The complexity of this use exceeded my initial conceptual
expectations. The primary research question “Do northern red-legged frogs show a
preference for a human-created forest opening with grasses, forbs and gardens over
adjacent undeveloped forest?” implicitly suggested that some frogs might use open
habitat, while other frogs might use natural forest habitat. While I did have a higher rate
70
of frog observations during area-constrained surveys in the open versus forest habitat,
this was not significantly different (p = 0.14, see results). In addition, frogs may have
been easier to find in open habitats, voiding the comparability of encounter rates in open
versus forest habitats.
However, the pattern of habitat use by northern red-legged frogs proved to be much
more complex. Importantly, through varied techniques, I discerned that the same frog
could be using both open and forest strata (e.g., Fig. 18). The open habitat was more
often moist during the warm summer through early fall, warm droughty conditions (Fig.
12), and for some frogs, may have provided critical moisture needs during otherwise
droughty conditions. In addition, use of the open area by frogs found in the forest edge
indicated that open habitat was used in tandem with forest habitat. My observations were
similar to those of Chan-McLeod (2003) who reported a quick retreat into the forest from
northern red-legged frogs that moved into a clearcut, as well as their maintaining a close
distance (12.7 m) to the forest edge, and to Haggard (2000) who found that whe re
northern red-legged frogs were in grassland near thicket/forest habitat, they were “usually
near or at the edge of the thicket/forest.” Thus it is possible that open terrestrial habitat
without nearby complex forest habitat could be unsuitable for northern red- legged frog
active season use.
Furthermore, after mid-October when conditions became moist but cool, I only found
frogs in native forest habitat with complex shrub, leaf and wood accumulations. These
inferences suggest that at terrestrial locations similar to the study area, forest habitat is a
requirement for northern red-legged frogs during both the active and overwintering
seasons.
Synthesis of Moisture and Temperature Data and Behaviors
“Pity the poor frog, his behavioral and physiological problems are so complicated
and interrelated, it is amazing that we can understand them and that he is alive at all!!”
Bayard Brattstrom (1979).
Northern red- legged frogs switch from being in water most of the time immediately
post-breeding (Shean 2002), to becoming mostly terrestrial during the active season
(Haggard 2000; this thesis). Patterns of habitat use and environmental conditions that I
71
observed lead me to hypothesize that feeding is a primary driver for frogs in their active
season. However, as conditions become dry and warm as summer progresses, reduced
availability of moisture and thus potentially increased risk of desiccation, may limit frog
activity and the ability to be surface active and feeding. Late fall to early winter, the
presence of frogs above ground at temperatures
7 C leads me to additionally
hypothesize that feeding remains a priority.
This study demonstrated that the highest frog growth rates occurred spring through
mid- fall. Thus, it may be that conditions suitable for feeding and favorable for growth
and survival during the extended active terrestrial and overwintering intervals are critical
for northern red- legged frogs. I hypothesize that a limiting environmental factor during
warm droughty terrestrial conditions is moisture, and during cooler moist conditions a
limiting factor is temperature.
Preliminary Model for Hypothesized Limiting Factors (Moisture and Temperature)
Figure 27 provides a preliminary season-based model to explain northern red- legged
frog use of terrestrial habitat as a function of temperature and moisture.
Spring through early summer-- A focal assumption of the model is that until early
summer, moisture conditions (e.g., see Figs. 10, 11, 12) typically do not limit frog
activity. However, in early summer, a transition period occurs during which the prism of
moist habitat quickly begins to contract (Fig. 12), and moist sites became patchy on the
landscape. Surface visible frogs that I located during this time were found in these moist
patches. Haggard (2000) reported a similar observation for northern red- legged frogs in
northern California. Hence, the first pattern observed associated with the changing
moisture regime was the use of habitat that remained moist.
Northern red- legged frogs may prefer moist substrate, and use it as long as possible
before initiating dry habitat behaviors. This use pattern appears similar to that which
Heatwole (1961) identified for wood frogs. When wood frogs were provided with a
choice of wet muck or leaf litter and bark, the frogs were always on the moist muck.
However, when he allowed the substrate to begin drying, the frogs showed an increased
preference for being under cover.
72
SPRING (20-Mar to 20-Jun)
Moisture and thermal regimes: All
EARLY SUMMER (21-Jun to 8-Jul)
Moisture and thermal regimes: Habitat begins to dry (av. rainfall 1.9 mm/day, 17% of days have
habitat typically moist to saturated (av.
rainfall 2.3 mm/day, 41% of days have rain);
temperatures moderate (av. air 12.3 C).
Frog response and limitations: Feedings
and movement opportunities readily available.
Assumption: Moisture not limiting for frog
activities; temperatures above ca.
9.3 C provide movement opportunity.
rain); temperatures moderate (av. air 13.9 C).
Forest habitat becomes increasingly dry; microhabitats, e.g., downed wood and leaf accumulations at
sword fern bases continue to retain moisture.
Open habitat may have morning dew and guttation moisture.
Intermittent rains provide moisture to many habitats, but most quickly dry. Areas at the base of concave
topographic locations, and under dense cover retain moisture longer.
Frog response and limitations: Frogs begin to use the moist spectrum of habitats. This spectrum
spatially and temporally expands with rainfall. Use may be related to feeding, moisture retention and
absorption, temperature regulation, or other needs.
Assumption: Moisture and temperature are becoming limiting for frog activities.
MID-FALL THROUGH EARLY WINTER (25Sep to 31-Dec)
Moisture and thermal regimes: Habitats moist to
saturated (av. rainfall 4.6 mm/day, 61% of days have
rain); temperatures increasingly cool (av. air 7.2 C),
ground on av. (9.0 C), is warmer than air.
Frog response and limitations:
-Below 10 C air and ground, frogs are primarily below
100% near-space vegetation cover, and below 7 C frogs
are subsurface below leaf duff or duff and soil.
-Feeding possible in sheltered locations during cool
weather (e.g., 7 to 10 C air and ground) and openly
visible locations when air is warmer, including
conditions where air is warmer than ground (e.g., air 12
C, ground 11 C).
-Frogs may use large rain events to travel to winter home
ranges. When temps. drop below ca. 9.3 C, migration
halts and frogs use migratory stop-over sites with
complex native vegetation.
Assumptions: Cold temperatures limit frog activity.
MID-SUMMER THROUGH EARLY FALL (9-Jul to 24-Sep)
Moisture and thermal regimes: Most habitat is dry (av. rainfall 0.8 mm/day, 22% of days have
rain), temperatures warm to hot but begin to cool early fall (av. air 15.0 C), av. ground
temperatures cooler than air (14.4 C).
-In forest, only decaying down wood routinely retains moisture.
-Open habitat may have morning dew and guttation moisture; human watering creates moist
patches.
-Intermittent rains create ephemeral moist conditions with less observed moisture under conifers
than under deciduous trees or in open areas.
-Small tidal/freshwater channel and nearshore tidal habitats are moist.
Frog response and limitations:
-Use of dry sub-surface habitats presumably for protection from heat and dehydration.
-Use of rain events to become more active (e.g., emerge from sub-surface habitat, and/or move to
different locations than being used during prolonged dry spells).
-Absorption of moisture from limited sources.
-Burrowing after absorbing moisture within or under dense dry leaf litter.
-Use of dry open habitat for feeding, after pobtaining moisture elsewhere.
-Cool early morning use of open habitats near forest edge for feeding (and possible moisture
absorption).
Assumption: Moisture and temperature conditions are limiting.
Figure 27. Model showing observed responses to moisture and temperature gradients by northern red-legged frogs at a terrestrial
study site in the Puget Lowland Ecoregion from spring through early winter.
73
Mid-summer to early fall dry, warm conditions -- Varied behavior patterns were
associated with dry, warm terrestrial conditions mid-summer through early fall. My
observations of visibly moist northern red- legged frogs in crouch positions on watered
garden soils, suggest that the frogs were absorbing soil moisture cutaneously, and
utilizing evaporative cooling. Research on other anurans supports this possibility. For
example, Shoemaker et al. (1992) summarize literature on amphibian use of soil moisture
to obtain body moisture. They report that amphibians use close contact with the soil, as
well as accumulation of solutes to reduce the animal’s water potential, as adaptations that
allow intake of soil water. Carter (1979) provides an overview of literature that
documents the permeable nature of frog skin including the exceptional permeability to
water of some ventral skin areas. He also states: “It is known that many frogs adopt a
distinctive posture when absorbing water from a moist surface.” Carpenter and
Gillingham (1987) presumed that giant toads (Bufo marinus) were absorbing moisture
where they appeared to be flattened into tire tracks, or onto a moist log.
I am not aware of literature specific to the use of evaporative cooling by northern redlegged frogs. However, literature reviews and discussion by Brattstrom (1963, 1979)
provide a basis for its occurrence during heat related stress and also as a “normal
mechanism of thermoregulation.” This physiological adaptation may allow amphibians
to be “more active longer” (Brattstrom 1979).
Research by Carter (1979) suggested that water absorbed through anuran skin may be
collected in lymph spaces. This could account for the “very wet” frogs I observed during
dry conditions, and potentially indicate an adaptation of northern red- legged frogs that
allows for water collection and storage during drought conditions.
Finding northern red- legged frogs on tidal mudflats during the warm and dry midsummer to early fall period was unanticipated. However, Balinsky (1981, cited in
Shoemaker et al. 1992) has reported that 61 species of anurans inhabit or tolerate
brackish water. Hayes (pers. comm. 2002) studied the California red- legged frog at
Pescadero Marsh (south of San Francisco along the California coast) in the 1980’s. Here
at levels of 4.5 ppt salinity, embryos died, and at 8.0 ppt salinity frogs vacated the area.
74
Three different frogs in my study were found in areas routinely flooded by tidal
waters 1 , and a fourth frog was found on the other side of the channel, indicating that it
had crossed the channel. Tidal channel, and near channel substrate salinities (Fig. 14)
measured near locations where I found frogs were below the 8.0 ppt salinity level
reported as causing California red- legged frogs to leave. Frogs at my study area may
have been obtaining water in the tidal zone. However, this environment may not have
been preferred, as indicated by the movement away from the shoreline by two
telemetered frogs following the 21 August 2001 rainfall. Microsite investigation of
salinity variation, freshwater inputs, and specific northern red- legged frog locations
would be useful to provide a better understanding of this species’ possible use of the tidal
area for obtaining moisture.
Northern red- legged frogs at my study area had home ranges that appeared to include
primary and backup areas for obtaining water during warm droughty conditions. In
particular, for two telemetered frogs with identified primary home ranges, one end of
each frog’s range had an apparent primary source, the buttercup and grass “shared
resource area”. Presumably when it no longer provided adequate moisture, the frogs used
the tidal channel as a backup source.
The highest measured air temperature during the study was 26.9 C and the highest
ground temperature was 21.0 C. Mean air temperatures for the three combined core
stations (spring, 12.3 C; early summer, 13.9 C; and mid-summer through early fall, 15.0
C), reflect conditions conducive to the preferred body temperature of 13.3 C for R.
aurora reported by Brattstrom (1963) 2 . The mean air temperature mid-summer through
early fall, taken 3.5 km from the study area in a developed, non- forested portion of The
Evergreen State College, was nearly a degree higher (15.8 C), suggesting the importance
of the forest and shoreline moderated climate at the study site.
Mid-fall to early winter-- Colder temperatures mid- fall through early winter
appeared to limit frog activity as I only found frogs in subsurface burrows at temperatures
1
My three direct observations of frogs in the tidal zone all occurred when the tide was out. I observed frog
424E61451B (see Appendix G) turning toward incoming tidal waters and then away, eventually hopping to
shore, and up a small cliff, when tidal waters approached within 10 cm.
2
Note that Brattstrom (1963) does not indicate subspecies for this data hence it is possible that data for the
California red-legged frog (R. aurora draytoni) may be included.
75
< 7 C. Based on this, it appears that should temperatures drop to a critical minimum1 the
frogs would be in protected locations moderated by the ground temperature.
During the increasingly cold mid-fall to early winter period, frogs may be selecting
habitat locations with a warmer microclimate. Average air and ground temperatures at
the shoreline cliff and the near shoreline site were the warmest recorded at the study site
mid- fall through early winter (Table 8). Both frogs telemetered throughout November
used migratory stop-over habitat on a slope within 5 to 10 m of the cove and may have
benefited from the warmer conditions. Winter habitat used by these same two frogs may
also represent selection for a warmer microclimate. One frog was on a south-facing
hillslope, and the other was on the nearby hillslope plateau. Both locations had favorable
insolation, but temperature data would be needed to verify a temperature advantage to
these locations.
1
I assume this would be similar to the -1 C critical minimum identified for R. cascadae and R. pretiosa by
Brattstrom (1968).
76
CHAPTER 7. SPECIES CONSERVATION
This chapter and its associated Appendix I, provide a focus on conservation needs of
northern red-legged frogs in the Puget Lowlands, and more broadly within Washington
State. The methods, results, and discussion for conservation interviews/surveys are
presented, as is a section discussing this study’s contribution to knowledge of the
northern red-legged frog, and recommendations for further study.
Introduction
Due to the rapid development expected within the next 20 years for the Puget Sound
(Washington Office of Financial Management 2002) and thus expected extensive
incremental habitat loss, northern red-legged frog populations in the Puget Lowlands face
considerable uncertainty for the future. It is unlikely that the current, widespread and
common nature of this species can be retained without specific knowledge of its life
history needs and protective measures focused toward these needs.
Northern red- legged frogs face double jeopardy from human impacts to both land and
water environments. One frog may not only require breeding, active-season, and
overwintering habitats, but migratory stop-over locations among these frequently
spatially distinct habitats may also be important (this thesis). All of these segments of
northern red-legged frog habitat are vulnerable to varying degrees to human-caused
changes. In addition, migration routes must increasingly cross roads and driveways
adding what may be a substantial direct source of mortality.
Work done by the Science and Environmental Health Network (2001) on the role of
science in the face of uncertainty and lack of data, provides a basis to consider northern
red-legged frog needs in developing landscapes. They advocate applying the
precautionary principle as a guide. This principle, as written in the Icicle Creek
Statement (Science and Environmental Health Network 2001), is as follows:
“When an activity or condition raises credible threats of harm to ecosystems,
precautionary measures should be taken, even if cause-and-effect relationships are not
fully established.”
O’Brien (2003) discusses two approaches for use of this principle. The traditional use
is as a “triggered brake”, a way of estimating where, for example, a specific activity will
77
drive a species to an unrecoverable population, and in the face of uncertainty, taking
precautionary measures to provide protection. A second approach is using the principle
“as a means to achieve positive public and environmental health goals.” This process is
initiated by developing a positive environmental health goal. A complex of activities is
then developed and implemented to achieve the goal, and a monitoring/feedback loop to
assure the process is effective at achieving the goal is included as part of the process.
For the purposes of this thesis, I adapted concepts from the above approach as a
framework for interviewing/surveying amphibian biologists during July of 2002. For the
survey, I specified a proactive conservation goal for red- legged frogs in Washington as
follows: “To maintain robust populations of red-legged frogs throughout their historical
range within Washington State.”
Although the emphasis of my research has been the Puget Lowland Ecoregion, the
survey specified the broader spatial area of the state. The purpose for the surveys was to
gather the following information:
1. Alternatives to enable achieving the proactive population goal, and,
2. Population status and vulnerability of the northern red- legged frog in Washington.
Methods: Conservation Surveys
During July 2002 I interviewed five scientists regarding northern red-legged frog
conservation in Washington. The persons I interviewed were: Marc Hayes, Research
Scientist, Washington Department of Fish and Wildlife; Klaus Richter, Senior Ecologist,
King County Department of Natural Resources; Kelly McAllister, Regional Wildlife
Biologist, Washington Department of Fish and Wildlife; J. Tuesday Serra Shean,
Wetland Biologist, Washington State Department of Transportation; and, Mike Adams,
Research Ecologist, US Geological Service. Interviews were held in person with Marc
Hayes, Klaus Richter and Kelly McAllister, through written responses with J. Tuesday
Serra Shean and Mike Adams, and they included additional written responses from Klaus
Richter.
Results and Discussion
Respondents described Washington populations as being in the heart of the species’
range, which was expected to lend benefits for survivability. However, populations in
78
rapidly developing areas (e.g., much of King County) were felt to be vulnerable. Overall,
the survey documented that we have small amounts of demographic data, broad but not
specific location information, poor status and trends data, poor information on thresholds
of concern for population decline and for habitat loss; and some local efforts, but no
broad monitoring programs that include this species.
Based on survey results I erected a system with six components for achieving the
above- noted goal. Components are (1) a research and monitoring effort to support all
aspects of protection, (2) immediate protection needs for rapidly developing areas where
red-legged frogs are currently most vulnerable, (3) public education about the needs of
northern red-legged frogs, (4) inclusion in and adjustments to the state conservation
status program, (5) exotic species measures, and (6) adaptive management to assure new
information is incorporated into protective components and that the system is effective at
achieving the overarching goal. This system is outlined in Table 14. Further details and
additional survey results are provided in Appendix I.
Table 14. Components of a system to achieve the goal: "To maintain robust populations
of northern red-legged frogs throughout their historical range within Washington State ."
1. Research and Monitoring
4. State Conservation Status
a. Geographic presence linked with population
a. Inclusion in state monitor status
condition index sites
b. Update of state conservation system to
b. Demographic and habitat research
address regional needs
c. Landscape analysis for rapidly developing areas
5. Exotic Species
2. Protection in Rapidly Developing Areas
a. Prevent the spread of exotic fish
a. Habitat needs and normal hydrology
b. Remove exotic fish from some areas
b. Protection of population core areas
c. Maintain bullfrog-free wetlands
c. Protection of ephemeral wetlands
d. Stormwater pond measures
6. Adaptive Management
a. Share and incorporate new information
into system
3. Education
a. Volunteer egg mass surveys
b. Assure that system is achieving goal
b. Children's programs
c. Brochures for habitat needs
d. News and television programs
Each system component, potentially in combination with other wildlife protective
work, is a unit that can be accomplished. System components complement each other
79
and all provide worthwhile endeavors in support of Washington’s red- legged frog
populations.
This Study’s Contribution to Conservation of the Northern Red-Legged
Frog, and Recommendations for Further Study
There has been limited research to date focused on terrestrial habitat use by northern
red-legged frogs. This study importantly has provided a framework for recognizing some
of the complexities that are involved in terrestrial use, (e.g., demographic components,
moisture and thermal requirements, movement and differing seasonal habitat
requirements and other patterns of behavior). Overall study results indicate numerous
avenues of susceptibility to population impact from landscape changes that result from
development. It is imperative that we better understand how northern red- legged frogs
use habitat, directed at providing information that can be used for their protection.
As such, complementary to elements listed in Table 14, I recommend the following
research regarding northern red- legged frog terrestrial habitat use and conservation:
•
Terrestrial active season and overwintering habitats.
1. What are key characteristics of terrestrial active season, and overwintering
habitats (e.g., plant communities, proximity to streams or other waters including
breeding areas, factors that may elucidate insolation advantage for overwintering
habitat, and how habitat is linked to trophic structures and northern red- legged
frog diet)?
2. Development of a model that will assist with knowing where terrestrial habitat use
is most likely to occur.
•
Movement between breeding, active season, and overwintering habitats.
1. Clarification and specifics regarding when the frogs are most likely to be moving
(e.g., seasons and dates, climatic conditions).
2. What are characteristics of where the northern red- legged frogs move on the
landscape? Can these be identified and modeled before an area is developed to
provide protection for migratory pathways?
3. What measures would be effective at protecting the frogs from vehicle mortality?
•
Meta-population structures.
1. Do meta-population structures exist for northern red- legged frogs?
2. If so, how do they function, and what are necessary measures to assure their
protection?
80
CHAPTER 8. KEY FINDINGS
Demographics
• Based on a Schnabel population estimate, the number of frogs using the study area in
2001 was estimated to be 60 (95% confidence interval of +/- 81). This equates to 31
frogs per ha. Based on expanded data from 2001 area-constrained searches the
maximum population was 78 frogs. Fifty- four frogs were uniquely identified in 2001.
•
Frogs ranged from 36 to 79 mm SVL, and from 3 to 48 g. The mean of the maximum
SVL measured for known females in 2001 was 69.3 mm. The SVL of known males
(n = 3, for 2000 to 2002) ranged from 51 to 59 mm. The mean of the maximum mass
measured for known females in 2001 was 35.8 g. The masses of known males (n = 3)
ranged from 11 to 23 g.
•
Daily growths rate (as SVL) and increases in mass were greater spring through midfall as compared to the full year (SVL: p = 0.0023), suggesting the importance of this
interval in relation to feeding.
Behavior
• Frogs utilized terrestrial habitat from April through December.
•
A higher rate of capture for frogs occurred in the open stratum (during areaconstrained surveys) than in the forest stratum, but capture rates were not
significantly different between strata (p = 0.14) and potentially confounded by
differential detection rates between strata.
•
Primary active season home ranges were used for at least 4 to 5 months. Three
primary home ranges identified were 62 to 80 m long, and 9 to 18 m wide. Individual
home ranges included open and forest habitats as well as a tidal channel.
•
At least some frogs returned to the same active season home ranges in subsequent
years. In 2002, of five frogs present during the summer, two were also observed in
2001, and one had also been observed in both 2000 and 2001.
•
Two female frogs were tracked to winter home ranges. They were located on a
southwest facing forested hillslope, across the salt-water cove from the study area.
•
A preliminary ethology of northern red- legged frog behavior in its natural terrestrial
environment was developed. Categories are: postural, distance movement, in-place
81
movement, movement patterns and home ranges, physiology, predator/danger
responses, habitat modification, vocalization and social structure.
•
Video footage taken August and September 2001 showed frogs were motionless
99.5% of the time. There were 181 sec of movement during 11 hr of observation.
During these seconds, there were 123 movement episodes, and these included 149
individual behaviors (i.e., some episodes had > 1 behavior). The frogs had an insect
capture rate of one per 3.7 hr.
•
Spring through early winter moisture and temperature regimes elicited behavior
patterns from the frogs that suggested being able to remain actively feeding was
important. The frogs used multiple approaches to obtain moisture that presumably
allowed surface activity such as feeding to continue. A preliminary model was
developed to explain observed responses.
•
During early summer through early fall, the 3-day antecedent rainfall was a useful
predictor of the mean number of frogs observed during area-constrained surveys.
Most frogs were observed when there had been > 3.0 mm of rain. Only two frogs
were found during the seven surveys that had no 3-day antecedent rainfall.
•
At
10 C air and ground temperatures frogs were found sub-surface, on the ground,
and elevated on vegetation or wood. Between 7 and 10 C air and ground, frogs were
almost always found below 100% near-space cover, or in sub-surface burrows.
Below 7 C air and ground, frogs were only found in sub-surface burrows.
•
Spring and fall migrations included a diversity of timings and patterns. Migration
stopped in the fall when temperatures were below ca. 9.3 C, and reinitiated when
conditions warmed up, concurrent with rain.
•
After mid-October, frogs were only found in native forest habitat with complex shrub,
leaf and wood accumulations.
Conservation
• At terrestrial locations similar to the study area, forest habitat appears to be a
requirement for northern red-legged frogs during both active and overwintering
seasons.
82
•
The major source of observed mortality to adult frogs was vehicle travel on a
residential road crossed by frogs during spring and fall. This serious issue should be
hypothesized as being within the top group of threats to northern red- legged frog
populations in areas of development.
•
Based on surveys of amphibian biologists, I outlined a system to achieve long-term
robust populations for this species throughout its range in Washington. Components
are research and monitoring, protection in rapidly developing areas, education, state
conservation status, control of exotic species, and an adaptive management process to
assure that progress is being made in achieving protection.
83
LITERATURE CITED
Adams, M.J. 1999. Correlated factors in amphibian decline: exotic species and habitat
change in western Washington. Journal of Wildlife Management. 63:1162-1171.
Adams, M.J. 2000. Pond permanence and the effects of exotic vertebrates on anurans.
Ecological Applications. 10(2): 559-568.
Adams, M.J. 2002. Personal communication. Research ecologist, Washington and
Oregon, USGS Forest and Rangeland Ecosystem Science Center. Corvallis, OR.
Adams, M.J., R.B. Bury and S.A. Swarts. 1998. Amphibians of the Fort Lewis Military
Reservation, Washington: sampling techniques and community patterns. Northwestern
Naturalist. 79:12-18.
Adams, M.J., S.D. West and L. Kalmbach. 1999. Amphibian and reptile surveys of U.S.
Navy lands on the Kitsap and Toandos Peninsulas, Washington. Northwestern Naturalist.
80:1-7.
Balinsky, J.B. 1981. Adaptation of nitrogen metabolism to hyperosmotic environment in
Amphibia. Journal of Experimental Zoology. 215:335-350. Cited in: Shoemaker, V.H.,
S.S. Hillman, S.D. Hillyard, D.C. Jackson, L.L. McClanahan, P.C. Withers and M.L.
Wygoda. 1992. Exchange of water, ions, and respiratory gases in terrestrial amphibians.
Pages 125-150 in Feder, M.E. and W.W. Burggren, editors. Environmental physiology
of the amphibians. The University of Chicago Press. Chicago, IL.
Beasley, B.A. 2002. The splat project: Monitoring amphibian movements and mortality
on a highway crossing the coastal flats of Clayoquot, B.C. in: Moon, B. editor. 2002
annual meeting; Society for Northwestern Vertebrate Biology; Gorgeous wildlife of the
Pacific Northwest; April 3-6; Hood River, OR. Society for Northwest Vertebrate
Biology.
Brattstrom, B.H. 1963. A preliminary review of the thermal requirements of
amphibians. Ecology. 44(2):238-255.
Brattstrom, B.H. 1968. Thermal acclimation in anuran amphibians as a function of
latitude and altitude. Comparative Biochemistry and Physiology. 24:93-111.
Brattstrom, B.H. 1979. Amphibian temperature regulation studies in the field and
laboratory. American Zoologist. 19:345-356.
Brattstrom, B.H. and P. Lawrence. 1962. The rate of thermal acclimation in anuran
amphibians. Physiological Zoology. 35:148-156.
84
Brown, H.A. 1975. Reproduction and development of the northern red- legged frog,
Rana aurora, in northwestern Washington. Northwest Science. 49(4):241-252.
Carpenter, C.C. and J.C. Gillingham. 1987. Water hole fidelity in the marine toad, Bufo
marinus. Journal of Herpetology. 21(2):158-161.
Carter, D.B. 1979. Structure and function of the subcutaneous lymph sacs in the Anura
(Amphibia). Journal of Herpetology. 13(3):321-327.
Chan-McLeod, A.C. 2003. Factors affecting the permeability of clearcuts to red- legged
frogs. Journal of Wildlife Management. 67(4):663-671.
COSEWIC (Committee on the status of endangered wildlife in Canada). 2002.
COSEWIC database. (Accessed 27 May 2002, Http://www.cosewic.gc.ca/eng/sct1.html).
Dumas, P.C. 1966. Studies of the Rana species complex in the Pacific Northwest.
Copeia. 1:60-74.
Dvornic h, K.M., K.R. McAllister, and K.B. Aubry. 1997. Amphibians and reptiles of
Washington State: Location data and predicted distributions, Volume 2 in Washington
State Gap Analysis – Final Report, (K.M. Cassidy, C.E. Grue, M.R. Smith and K.M.
Dvornich, eds.), Washington Cooperative Fish and Wildlife Research Unit, University of
Washington, Seattle.
Fitch, H.S. 1936. Amphibians and reptiles of the Rogue River Basin, Oregon. American
Midland Naturalist. 17(3):634-652.
Gregory, P.T. 1978. Feeding habits and diet overlap of three species of garter snakes
(Thamnophis) on Vancouver Island. Canadian Journal of Zoology. 56:1967-1974.
Gregory, P.T. 1979. Predator avoidance behavior of the red-legged frog (Rana aurora).
Herpetologica. 35(2):175-184.
Haggard, J.A. 2000. A radio telemetric study of the movement patterns of adult northern
red-legged frogs (Rana aurora aurora) at Freshwater Lagoon, Humboldt County,
California [MAB thesis]. Arcata (CA): Humboldt State University.
Hall, J.D. 1992. Introductory population dynamics lecture/lab notes. Oregon State
University. Corvallis, OR.
Hayes, M.P. 2001, 2002, 2003, 2004. Personal communication. Research biologist with
Washington Department of Fish and Wildlife. Olympia, WA.
Hayes, M.P., C.A. Pearl and C.J. Rombough. 2001. Rana aurora aurora (Northern redlegged frog): Movement. Herpetological Review. 32(1):35-36.
85
Hayes, M.P. and C.B. Hayes. 2003. Rana aurora aurora (Northern red- legged frog):
Juvenile growth: Male size at maturity. Herpetological Review. 34(3):233-234.
Hayes, M.P., C.B. Hayes and J.P. Schuett-Hames. 2004. Rana aurora aurora (Northern
red-legged frog): Vocalization. Herpetological Review. 35(1):52-53.
Heatwole, H. 1961. Habitat selection and activity of the wood frog, Rana sylvatica Le
Conte. American Midland Naturalist. 66:301-313.
Heyer, W.R., M.A. Donnelly, R.W. McDiarmid, L. C. Hayek and M. S. Foster. 1994.
Measuring and monitoring biological diversity; Standard methods for amphibians.
Smithsonian Institutional Press. Washington, D.C.
Lamoureux, V.S. and D.M. Madison. 1999. Overwintering habitats of radio-implanted
green frogs, Rana clamitans. Journal of Herpetology. 33(3): 430-435.
Leonard, B.P., H.A. Brown, L.L.C. Jones, K.R. McAllister and R.M. Storm. 1993.
Amphibians of Washington and Oregon. Seattle Audubon Society.
Licht, L.E. 1969. Comparative breeding behavior of the red- legged frog (Rana aurora
aurora) and the western spotted frog (Rana pretiosa pretiosa) in southwestern British
Columbia. Canadian Journal of Zoology. 47(6):1287-1299.
Licht, L.E. 1971. Breeding habits and embryonic thermal requirements of the frogs,
Rana aurora aurora and Rana pretiosa pretiosa, in the Pacific Northwest. Ecology.
52(1):116-124.
Licht, L.E. 1974. Survival of embryos, tadpoles, and adults of the frogs Rana aurora
aurora and Rana pretiosa pretiosa sympatric in southwestern British Columbia.
Canadian Jounal of Zoology. 52:613-627.
Licht, L.E. 1986. Food and feeding behavior of sympatric red- legged frogs, Rana
aurora, and spotted frogs, Rana pretiosa in southwestern British Columbia. Canadian
Field-Naturalist. 100(1):22-31.
Mattoon, A. 2000. Amphibia fading. World Watch. 13(4):12-23.
McAllister, K. 2002. Personal communication. Regional wildlife biologist for Thuston
and Pierce Counties, Washington Department of Fish and Wildlife. Olympia, WA.
Milne, D.E. 2002. Personal communication. Professor, MES Program, The Evergreen
State College. Olympia, WA.
Norse, E.A. 1990. Ancient forests of the Pacific Northwest. Island Press. Washington,
D.C.
86
Nussbaum, R.A., E.D. Brodie and R.M. Storm. 1983. Amphibians and reptiles of the
Pacific Northwest. University of Idaho Press, Moscow, ID.
O’Brien, M. 2003. Science in the service of good: The precautionary principle and
positive goals. Pages 279-295 in Tickner, editor. Precaution, environmental science, and
preventive public policy. Island Press. Washington, D.C.
Oregon Department of Fish and Wildlife. 1997. Oregon Departme nt of Fish and
Wildlife Sensitive Species. (Accessed 11 November 2003,
Http://www.dfw.state.or.us/ODFWhtml/InfoCntrWild/ Diversity/sensspecies.pdf).
Omernik, J.M. 1987. Ecoregions of the conterminous United States. Annals of the
Association of American Geographers. 77:118-125.
Omernik, J.M. and A.L. Gallant. 1986. Ecoregions of the Pacific Northwest.
EPA/600/3-86/003. United States Environmental Protection Agency. Corvallis, OR.
Ostergaard, E.C. 2001. Pond-breeding amphibian use of stormwater ponds in King
County, Washington [MSc thesis]. Seattle (WA): University of Washington.
Rabinowe, J.H., J.T. Serra, M.P. Hayes and T. Quinn. 2002. Rana aurora aurora
(Northern red-legged frog) diet. Herpetological Review. 33(2):128.
Rathbun, G.B. and T.G. Murphey. 1996. Evaluation of a radio-belt for Ranid frogs.
Herpetological Review 27(4):187-189.
Richards, S.J., U. Sinsch and R.A. Alford. 1994. Radio tracking. Pages 155-158 in
W.R. Heyer, M.A. Donnelly, R.W. McDiarmid, L.C. Hayek, and M.S. Foster, editors.
Measuring and monitoring biological diversity: Standard methods for amphibians.
Smithsonian Institution Press. Washington, D.C.
Richter, K.O. 2002. Personal communication. Senior ecologist with King County
Department of Natural Resources. Seattle, WA.
Richter, K.O. and E.C. Ostergaard. 1999. King County wetland-breeding amphibian
monitoring program: 1993-1997 summary report. King County Department of Natural
Resources, Water and Land Resources Division. Seattle, WA.
Ritson, P.E. and M.P. Hayes. 2000. Late season activity and overwintering in the
northern red-legged frog (Rana aurora aurora). Final report to the U.S. Fish and
Wildlife Service. Portland, OR.
Shoemaker, V.H., S.S. Hillman, S.D. Hillyard, D.C. Jackson, L.L. McClanahan, P.C.
Withers and M.L. Wygoda. 1992. Exchange of water, ions, and respiratory gases in
terrestrial amphibians. Pages 125-150 in Feder, M.E. and W.W. Burggren, editors.
87
Environmental physiology of the amphibians. The University of Chicago Press.
Chicago, IL.
Schuett-Hames, D.E., A.E. Pleus, E. Rashin and J. Matthews. 1999. TFW monitoring
program method manual for the stream temperature survey. TFW-AM9-99-005.
Washington Department of Natural Resources. Olympia, WA.
Science and Environmental Health Network. 2001. Icicle Creek statement on the
precautionary principle and ecosystems. (Accessed 12 April 2003,
Http://www.sehn.org/icicle.html).
Shean, J.T. 2002. Personal communication. Wetland biologist with Washington
Department of Transportation. Olympia, WA.
Shean, J.T. 2002. Post-breeding movements and habitat use by the northern red- legged
frog, Rana aurora aurora, at Dempsey Creek, Thurston County, Washington [MES
thesis]. The Evergreen State College. Olympia, WA.
Smith, R.L. 1974. Ecology and field biology; Second edition. Harper & Row,
Publishers. New York.
Storm, R.M. 1960. Notes on the breeding biology of the red- legged frog (Rana aurora
aurora). Herpetologica. 16:251-259.
Tuxill, J. 1998. Losing stands in the web of life: Vertebrate declines and the
conservation of biological divesity; Worldwatch paper 141. Worldwatch Institute.
Washington D.C.
U.S. Fish and Wildlife Service. 2000. California red- legged frog recovery plan available
for public review. (Accessed 18 November 2000, Http://pacific.fws.gov/new/200089.htm).
Washington Department of Fish and Wildlife. 2002. Species status. (Accessed 24 June
2002, Http://www.wa.gov/wdfw.html).
Washington Office of Financial Management. 2002. 2002 population trends for
Washington State. Office of Financial Management. Olympia, WA.
88
APPENDIX A. Year 2001 survey type and number of frogs.
Table A-1. Frog survey data. Gray indicates no survey. Data exclusively from telemetry
were not included.
Season
Date
Time/ Oppor- Trap Grand Season
Date Time/ Oppor- Trap Grand
Area tunistic No. Total
Area tunistic No. Total
No.
No.
No.
No.
Spring
3-Apr
0
0
0
Early Fall 25-Aug
4
4
20-Mar to
21-Apr
1
1
22-Aug to 26-Aug
3
3
6
20-Jun
23-Apr
0
1
1
24-Sep
3-Sep
2
2
4
2-May
1
0
1
4-Sep
1
1
2
7-May
4
0
4
9-Sep
1
1
15-May
0
0
0
10-Sep
0
1
1
19-May
1
1
11-Sep
1
1
2
21-May
2
0
2
12-Sep
0
0
0
28-May
2
0
2
13-Sep
1
0
1
29-May
1
1
14-Sep
1
0
1
3-Jun
1
1
15-Sep
2
0
2
4-Jun
1
2
3
17-Sep
1
2
3
10-Jun
1
1
18-Sep
0
0
0
11-Jun
0
0
0
19-Sep
2
0
2
15-Jun
2
2
20-Sep
0
0
0
18-Jun
1
1
2
22-Sep
1
1
Early
25-Jun
3
1
4
23-Sep
3
3
Summer
28-Jun
1
1
24-Sep
1
1
2
21-Jun to
1-Jul
1
1
Mid-Fall
25-Sep
1
1
2
8-Jul
2-Jul
0
1
1
25-Sep to 26-Sep
3
0
3
3-Jul
0
0
0
27-Nov
27-Sep
0
0
0
4-Jul
0
0
0
30-Sep
6
0
6
8-Jul
2
2
1-Oct
1
0
1
Mid through
9-Jul
0
1
1
8-Oct
2
2
4
Late
12-Jul
1
1
9-Oct
0
0
0
Summer
14-Jul
1
1
14-Oct
2
2
9-Jul
15-Jul
3
3
15-Oct
1
0
1
21-Aug
16-Jul
2
1
3
16-Oct
0
0
0
17-Jul
0
0
0
22-Oct
0
0
0
18-Jul
0
0
0
23-Oct
0
0
0
23-Jul
0
0
0
24-Oct
0
1
1
24-Jul
0
0
0
30-Oct
0
0
0
28-Jul
3
3
31-Oct
0
0
0
30-Jul
1
0
1
1-Nov
0
0
0
31-Jul
0
0
0
2-Nov
0
1
1
2-Aug
1
1
3-Nov
0
1
1
6-Aug
4
1
5
4-Nov
0
0
0
7-Aug
2
0
2
5-Nov
0
0
0
38
69
9 116
13-Aug
0
1
1
Total all seasons:
14-Aug
0
0
0
18-Aug
1
1
Number of surveys
19-Aug
1
1
Time-constrained: 7 (60-min, prior to 4 June)
20-Aug
1
0
1
Area-constrained: 21 (90-min, starting 4 June)
21-Aug
0
3
3
Trap days: 33
89
APPENDIX B. Area-constrained survey data.
Table B-1. Area-constrained survey catch totals (2001).
Survey
Date
4-Jun
11-Jun
18-Jun
25-Jun
2-Jul
9-Jul
16-Jul
23-Jul
30-Jul
6-Aug
13-Aug
20-Aug
26-Aug
3-Sep
10-Sep
17-Sep
24-Sep
30-Sep
8-Oct
15-Oct
22-Oct
Total all surveys:
Mean all surveys:
2,b
Mean/100 m :
2
Mean/km :
Forest
Open
Total
No. Frogs
2
2
2
Frogs/ 9 100 m Frogs/ 6 100 m Frogs/ 15 100 m
Estimated for
Quadrats
Quadrats
Quadrats
Full Study Areaa
1
0
0
2
0
0
2
0
0
2
0
1
1
1
0
0
0
4
0
0
0
0
0
1
1
0
0
0
0
1
2
0
0
2
1
0
1
1
2
2
1
0
1
0
1
3
0
0
2
0
1
4
0
1
3
2
0
1
1
6
2
1
0
13
0
13
39
0
0
26
0
13
52
0
13
39
26
0
13
13
78
26
13
0
14
0.67
0.07
15
0.71
0.12
29
1.38
0.09
92.06
377
17.95
0.09
a
2
The weekly estimate for the full study area = 13 times the total frogs per 100 m for the 15
surveyed quadrats. The total number of quadrats in the study area is 195, i.e., 13 x 15.
b
Based on a Wilcoxon Rank Sum Test, population locations for the forest and open strata are not
significantly different (p = 0.14).
90
APPENDIX C. Schnabel population estimate.
Table C-1. Tag status of area-constrained search day frog captures. This data set was
used for the Schnabel mark and recapture population estimate.
Date
Frog ID
Survey
Type
PIT Tag
No. a
Tag New on
Area-Constrained Days
4-Jun-01
18-Jun-01
18-Jun-01
25-Jun-01
25-Jun-01
16-Jul-01
16-Jul-01
30-Jul-01
6-Aug-01
6-Aug-01
13-Aug-01
20-Aug-01
26-Aug-01
26-Aug-01
26-Aug-01
26-Aug-01
26-Aug-01
26-Aug-01
3-Sep-01
3-Sep-01
3-Sep-01
3-Sep-01
10-Sep-01
17-Sep-01
17-Sep-01
24-Sep-01
24-Sep-01
30-Sep-01
30-Sep-01
30-Sep-01
30-Sep-01
8-Oct-01
8-Oct-01
8-Oct-01
15-Oct-01
6-4-01#1
6/18/01#1
6/18/01#2
6/25/01#1
6/25/01#4
7/16/01#2
7/16/01#3
7/30/01#1
8/6/01#1
8/6/01#2
8/13/01#2
8/20/01#1
8/26/01#1
8/26/01#2
8/26/01#3
8/26/01#4
8/26/01#5
8/26/01#7
9/3/01#1
9/3/01#2
9/3/01#3
9/3/01#4
9/10/01#1
9/17/01#2
9/17/01#3
9/24/01#1
9/24/01#2
9/30/01#2
9/30/01#3
9/30/01#5
9/30/01#6
10/8/01#1
10/8/01#2
10/8/01#4
10/15/01#1
opportunistic
area-constrained
opportunistic
area-constrained
opportunistic
area-constrained
area-constrained
area-constrained
area-constrained
area-constrained
opportunistic
area-constrained
area-constrained
opportunistic
opportunistic
area-constrained
area-constrained
opportunistic
area-constrained
opportunistic
area-constrained
opportunistic
opportunistic
opportunistic
opportunistic
area-constrained
opportunistic
area-constrained
area-constrained
area-constrained
area-constrained
opportunistic
opportunistic
area-constrained
area-constrained
424E61451B
43297F2700
424D19136C
had no tag
432E710B2C
43297C7D06
432E710B2C
432C7B7329
432E710B2C
432E765C59
432E6A3571
4329777564
had no tag
501D1A7724
50277C513C
5028025B2D
432C732F25
501C4C1C0D
43297F2700
432C744D14
50283B2579
50282F7027
432E775132
432C744D14
424E61451B
501C6A3723
501C746C25
501D1A7724
432C744D14
5027194621
501C6D0436
502043436A
501C795F00
501C77077D
50283B0B12
yes
yes
yes
escaped before marking
yes
yes
no
yes
no
yes
yes
yes
escaped before marking
yes
yes
yes
yes
yes
no
yes
yes
yes
yes
no
no
yes
yes
no
no
yes
yes
yes
yes
yes
yes
a
Bolded cells are those with recaptures on area-constrained search days.
91
APPENDIX D. Frog size, gender and age.
Table D-1. Frog measurements. Frogs with more than one measurement date are gray.
a
Pit Tag No.
Date
4232624532
4329641501
4329777564
5006572732
5006572732
5020521121
5027194621
42337F4E24
423A3A5332
423B2F1D33
423F27203A
423F40416A
424B0F344E
424D19136C
424D19136C
424D5D1C4A
424D5D1C4A
424D5D1C4A
424E124E23
424E511349
424E56143B
424E56143B
424E5C1D6E
424E5C1D6E
424E5D0C27
424E61451B
424E61451B
424E61451B
424E61451B
424F183401
424F1D0F35
424F2E3128
42500D1C53
425031621F
425031621F
4329433F18
4329657A24
432972620F
432972620F
43297C7D06
43297F2700
43297F2700
432B543D48
432C732F25
432C732F25
432C732F25
432C744D14
432C744D14
432C744D14
432C744D14
432C744D14
432C744D14
432C744D14
432C7B7329
432D000A12
432D641F2F
432D747F39
432E53200E
432E56314B
432E6A3571
432E6A3571
432E6A3571
432E710B2C
432E710B2C
432E710B2C
432E710B2C
432E710B2C
432E717657
432E765C59
31-Aug-00
18-Aug-01
20-Aug-01
1-Oct-01
13-Oct-01
26-Sep-01
30-Sep-01
23-Sep-00
23-Sep-00
1-Sep-00
1-Sep-00
31-Aug-00
1-Sep-00
7-May-01
15-Jun-01
31-Aug-00
8-Aug-01
2-Jul-02
7-Oct-00
5-Sep-00
1-Oct-00
23-Sep-01
25-Sep-00
19-May-01
25-Sep-00
2-May-01
4-Jun-01
28-Jul-01
4-Sep-01
23-Sep-00
31-Aug-00
28-May-01
31-Aug-00
7-Oct-00
9-Sep-01
28-Jul-01
10-Jun-01
28-Jun-01
28-Jul-01
16-Jul-01
18-Jun-01
3-Sep-01
8-Jul-01
14-Jul-01
26-Aug-01
23-Sep-01
15-Jun-01
15-Jul-01
28-Jul-01
20-Aug-01
3-Sep-01
17-Sep-01
30-Sep-01
30-Jul-01
2-Aug-01
3-Jun-01
25-Aug-01
29-May-01
21-May-01
1-Jul-01
8-Aug-01
13-Aug-01
25-Jun-01
16-Jul-01
6-Aug-01
10-Aug-02
6-Sep-02
8-Jul-01
6-Aug-01
a
b
b
SVL Shank
(mm) (mm)
52
63
63
67
49
56
56
61
52
43
54
50
55
59
52
55
58
46
76
51
66
52
61
53
67
69
69
72
53
51
49
50
58
71
40
55
46
51
45
61
65
55
59
64
66
65
68
68
68
68
70
71
61
66
60
62
71
60
55
58
57
60
61
63
73
74
58
40
39
32
39
Mass Gen(g)
der Age
31
32
27.0
21.5
33.0
35.0
13.0
16.0
35
36
17.0
23.0
34
32
16.0
15.0
M
M
M
M
M
38
29.5
F
F
F
36
25.0
39
40
42
42
31.0
34.0
35.0
35.0
29
11.0
40
23
35
29
31
27
36
37
35
34
37
39
39
40
40
42
39
42
40
37
40
36
38
39
36
35
34
33
36
38
38
42
42
36
25
38.0
6.0
18.0
10.5
13.0
8.0
27.0
28.0
13.0
21.5
25.5
27.5
31.0
34.0
32.5
30.0
33.0
34.0
36.5
24.0
30.5
22.0
27.0
36.0
23.0
17.0
19.0
19.0
23.0
24.0
25.5
38.0
37.0
16.0
5.5
F
F
min 1+
min 2+
min
min
min
min
0+
1+
0+
1+
F
F
F
F
F
F
min 0+
min 1+
F
F
F
F
F
F
F
F
F
F
F
F
F
F
min
min
min
min
min
1+
1+
1+
2+
2+
No. Yrs
Found
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
3
1
1
1
2
1
2
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
SVL is a measurement from the frog's snout to vent.
This is a measurement from the frog's knee to heel.
92
a
Pit Tag No.
Date
432E775132
432E775132
432E775132
501C400240
501C400240
501C400240
501C400240
501C400240
501C400240
501C400240
501C400240
501C4A103A
501C4A103A
501C4C1C0D
501C6A3723
501C6A3723
501C6D0436
501C6D0436
501C6F1873
501C6F1873
501C6F1873
501C6F1873
501C6F1873
501C6F7358
501C70012C
501C711D1A
501C746C25
501C75OD68
501C765374
501C765374
501C77077D
501C79216C
501C792B1E
501C792B1E
501C795F00
501C7D7167
501D1A221A
501D1A7724
501D1A7724
501D1B4040
501D1C5807
501D1F5C6E
501D213F44
501D23252F
501D25283B
501D25283B
501D25283B
501D263153
502043436A
50204D0501
50277C513C
5028025B2D
5028025B2D
5028025B2D
5028025B2D
5028025B2D
5028025B2D
5028025B2D
5028025B2D
5028025B2D
5028025B2D
50282F7027
50283B0B12
50283B2579
8/31/00#3
8/31/00#4
9/5/00#3
15-Jul-01
10-Sep-01
19-Sep-01
2-Nov-01
7-Nov-01
11-Nov-01
18-Nov-01
25-Nov-01
2-Dec-01
21-Dec-01
29-Dec-01
4-Sep-01
25-Sep-01
26-Aug-01
22-Sep-01
14-Oct-01
26-Sep-01
30-Sep-01
9-Jun-02
23-Jul-02
9-Aug-02
14-Aug-02
6-Sep-02
28-Sep-02
29-Apr-02
30-Jun-02
23-Sep-01
11-Sep-01
29-Jun-02
6-Jul-02
8-Oct-01
11-Sep-01
24-Oct-01
29-Nov-01
8-Oct-01
4-Oct-02
11-Jun-02
26-Aug-01
30-Sep-01
8-Sep-02
31-May-02
30-Jun-02
25-Aug-01
28-Sep-02
11-Sep-02
18-Sep-02
28-Sep-02
28-Sep-02
8-Oct-01
14-Oct-01
26-Aug-01
26-Aug-01
24-Sep-01
14-Oct-01
2-Nov-01
7-Nov-01
22-Jul-02
14-Aug-02
29-Aug-02
11-Sep-02
24-Sep-02
3-Sep-01
15-Oct-01
3-Sep-01
31-Aug-00
31-Aug-00
5-Sep-00
SVL Shank
(mm) (mm)
46
52
51
72
71
70
69
70
71
69
67
55
58
60
66
66
51
52
49
58
58
59
61
69
79
46
70
71
48
50
72
65
71
69
36
51
49
61
68
65
68
42
67
61
56
60
60
49
71
73
48
67
65
66
66
66
74
74
75
78
78
54
56
63
52
56
50
b
Mass Gen(g)
der Age
27
32
33
41
41
41
42
41
42
41
41
32
32
37
37
38
30
9.0
15.5
17.0
41.0
45.0
44.0
46.5
45.0
45.5
48.0
45.5
14.0
17.5
27.5
27.0
29.0
13.0
28
34
35
36
38
40
44
28
43
40
29
29.5
40
35
38.5
11.0
18.0
20.5
22.0
22.0
34.0
37.5
8.0
42.5
34.5
13.0
12.0
38.0
23.0
31.5
37.5
3.0
11.0
12.0
28.0
29.0
27.0
33.0
7.0
29.5
20.5
19.0
23.0
19.0
10.0
38.0
38.0
11.0
34.0
32.5
37.5
37.0
35.5
35.0
40.5
46.0
45.0
47.0
14.0
19.5
27.0
21
30
29
36
38
38
39
24
39
38
35
37
37
31
41
42
30
41
41
42
42
42
42
43
43
45
45
33
33
38
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
0+
M
F
F
F
F
F
F
F
F
F
F
F
F
F
min
min
min
min
min
min
min
min
min
min
1+
1+
1+
1+
1+
2+
2+
2+
2+
2+
No. Yrs
Found
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1
1
1
APPENDIX E. Growth data.
Table E-1. One-year snout-to-vent length growth, by gender, for six frogs.
Gender
Frog No.
Growth
(mm)
No. of
Days
Growth
per Day
(mm)
Growth
per Year
(mm)
15
358
0.04
15.29
13
338
0.04
14.04
10
368
0.03
9.92
13
366
0.04
0.04
0.006
12.96
13.05
2.30
Datea
SVL
(mm)
1-Oct-00
23-Sep-01
7-Oct-00
9-Sep-01
6-Aug-01
10-Aug-02
24-Sep-01
24-Sep-02
51
66
58
71
63
73
65
78
31-Aug-00
8-Aug-01
2-Jul-02
52
55
58
3
3
343
329
0.01
0.01
3.19
3.33
25-Sep-00
19-May-01
52
61
9
237
0.04
13.86
0.03
0.014
10.37
5.13
Female
424E56143B
425031621F
432E710B2C
5028025B2D
Mean females
s females
Male
424D5D1C4A
Unknown
424E5C1D6E
All
Mean all frogs
s all frogs
a
Measurements with the closest dates to a one-year interval were used.
93
Table E-2. Within-year snout-to-vent length growth, by gender, for 12 frogs a.
Gender
Dateb
SVL
(mm)
2-May-01
4-Sep-01
15-Jun-01
30-Sep-01
25-Jun-01
6-Aug-01
9-Jun-02
6-Sep-02
26-Aug-01
7-Nov-01
22-Jul-02
24-Sep-02
67
72
65
71
60
63
49
61
67
66
74
78
7-May-01
15-Jun-01
55
59
28-Jun-01
28-Jul-01
43297F2700
18-Jun-01
3-Sep-01
432C732F25
14-Jul-01
23-Sep-01
432E6A3571
1-Jul-01
13-Aug-01
432E775132
15-Jul-01
19-Sep-01
501D1A7724
26-Aug-01
30-Sep-01
Mean unknown gender
s unknown gender
46
51
61
65
59
66
55
57
46
51
61
68
Frog No.
No. of
Days
Growth
per Day
(mm)
Growth
per Year
(mm)
5
124
0.04
14.72
6
106
0.06
20.66
3
41
0.07
26.71
12
88
0.14
49.77
-1
72
-0.01
-5.07
4
63
0.06
0.06
0.05
23.17
21.66
17.79
4
38
0.11
38.42
5
29
0.17
62.93
4
76
0.05
19.21
7
70
0.10
36.50
2
42
0.05
17.38
5
65
0.08
28.08
7
34
0.21
0.11
0.07
75.15
39.87
23.91
0.09
0.06
31.36
21.39
Growth
(mm)
Female
424E61451B
432C744D14
432E710B2C
501C6F1873
5028025B2D
5028025B2D
Mean females
s females
Male
424D19136C
Unknown
432972620F
All
Mean all frogs
s all frogs
a
One female was measured two years bringing the total number of frogs listed to 13.
Measurements used were the earliest and latest (through mid-fall 27 November) for each frog.
b
94
Table E-3. One-year mass growth, by gender, for three frogs.
Gender
Frog No.
Datea
Mass (g)
Growth Growth
per Day per Year
(g)
(g)
Growth
(g)
No. of
Days
12.5
368
0.03
12.40
14.5
364
0.04
0.04
0.00
14.54
13.47
1.51
-1.0
329
0.00
-1.11
0.02
0.02
8.61
8.48
Female
432E710B2C
5028025B2D
6-Aug-01
10-Aug-02
24-Sep-01
24-Sep-02
25.5
38.0
32.5
47.0
8-Aug-01
2-Jul-02
16.0
15.0
Mean females
s females
Male
424D5D1C4A
All
Mean all frogs
SD all frogs
a
Measurements with the closest dates to a one-year interval were used.
95
Table E-4. Within-year mass growth, by gender, for 12 frogsa.
Dateb
Mass
(g)
2-May-01
4-Sep-01
15-Jun-01
30-Sep-01
25-Jun-01
6-Aug-01
26-Aug-01
7-Nov-01
22-Jul-02
24-Sep-02
9-Jun-02
6-Sep-02
31.0
35.0
31.0
36.5
23.0
25.5
34.0
35.5
35.0
47.0
11.0
22.0
7-May-01
15-Jun-01
Unknown 432972620F
28-Jun-01
28-Jul-01
43297F2700
18-Jun-01
3-Sep-01
432C732F25
14-Jul-01
23-Sep-01
432E6A3571
1-Jul-01
13-Aug-01
432E775132
15-Jul-01
19-Sep-01
501D1A7724
26-Aug-01
30-Sep-01
Mean unknown gender
s unknown gender
All
Mean all frogs
s all frogs
17.0
23.0
10.5
13.0
27.0
28.0
21.5
27.5
17.0
19.0
9.0
17.0
28.0
29.0
Gender
Frog No.
No. of
Days
Growth
per Day
(g)
4.0
124
0.03
11.77
5.5
106
0.05
18.94
2.5
41
0.06
22.26
1.5
72
0.02
7.60
12.0
63
0.19
69.52
11.0
88
0.13
0.08
0.07
45.63
29.29
23.75
6.0
38
0.16
57.63
2.5
29
0.09
31.47
1.0
76
0.01
4.80
6.0
70
0.09
31.29
2.0
42
0.05
17.38
8.0
65
0.12
44.92
1.0
34
0.03
0.06
0.04
10.74
23.43
15.05
0.08
0.01
28.77
4.14
Growth
(g)
Growth
per Year
(g)
Female
424E61451B
432C744D14
432E710B2C
5028025B2D
5028025B2D
501C6F1873
Male
Mean females
s females
424D19136C
a
One female was measured two years bringing the total number of frogs measured to 13.
The earliest and latest measurements (through mid-fall, 27 November) were used for each frog.
b
96
APPENDIX F. Study site temperature and moisture conditions.
Table F-1. Seasonal temperature and moisture regimes at the study site (2001).
Season
No.
Spring (20-Mar to 20-Jun)
Early summer (21-Jun to 8-Jul)
Mid-summer through early fall (9-Jul to 24-Sep)
Mid-fall through early winter (25-Sep to 31-Dec)
Rainfalla
Days
93
18
78
98
Temperatureb
Days w/ Rain- Av Rain
Air
Rain
fall per Day Max Min Av
Ground
Max
Min Av
No. %
(C)
38
3
17
60
a
41
17
22
61
(mm) (mm)
210
34
63
447
2.3
1.9
0.8
4.6
(C)
(C)
(C)
21.2
20.5
25.7
16.4
6.0
8.6
7.2
-0.1
12.3
13.9
15.0
7.2
(C)
17.3 11.7 14.4
14.3 3.4 9.0
Rainfall is from a gage at The Evergreen State College, located 3.5 km from the study site. Missing records were
filled with National Weather Service Olympia Airport data taken 15.5 km from the study site. On 28 November the
precipitation was snowfall.
b
These temperatures were derived from average hourly readings by combining data from three core sites in the
study area. Spring air temperatures are from 4 to 20 June only. Mid-summer through early-fall ground temperatures
are from 9 August to 24 September.
97
(C)
APPENDIX G. Telemetry results.
Table G-1. Overview of telemetry results for 10 female northern red- legged frogs.
Key
Frog identification number/Site use type
• Observation time-frame
• Total days within observation time-frame
• Number of days with observations
• Home range, use area length and width (m)
Frog #424E61451B
Primary active season home range.
• Time -frame: 2-May-01 to 17-Sep-01
• Total days: 139
• Observation days: 13
• Greatest home range size: L=62, W=11
Notes:
30-Jul: Frog on tidal flats by down tree. It hopped
2.5 m to shore when tidal waters were within 10 cm.
13-Aug: Frog on overhanging ledge/opening in cliff,
1 m down from top of cliff.
23-Aug: Location change concurrent with largest
rainfall (27 mm on 22-Aug) since 27-Jun.
4-Sep: Transmitter removed due to belt sores.
Date
Seasona
2-May-01
4-Jun-01
28-Jul-01
30-Jul-01
5-Aug-01
6-Aug-01
13-Aug-01
19-Aug-01
20-Aug-01
23-Aug-01
26-Aug-01
4-Sep-01
17-Sep-01
Sp
Sp
MLS
MLS
MLS
MLS
MLS
MLS
MLS
EF
EF
EF
EF
15-Jun-01
15-Jul-01
16-Jul-01
17-Jul-01
28-Jul-01
6-Aug-01
19-Aug-01
20-Aug-01
3-Sep-01
17-Sep-01
30-Sep-01
1-Oct-01
Sp
MLS
MLS
MLS
MLS
MLS
MLS
MLS
EF
EF
MF
MF
Telemetry
Start
and
End
Start
End
Observation
Type
Strata and Sub-Strata
Dist.
from
Last
Loc.
(m)
Frog
5m
from
Forest/
Open
Edge?
Time Search
Opportunistic
Opportunistic
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Opportunistic
Open (grass/forbs)
Open (grass/forbs)
Open (grass/forbs)
Forest (tidal channel)
Forest (shrub/shoreline cliff)
Forest (shrub/shoreline cliff)
Forest (shrub/shoreline cliff)
Forest (shrub/shoreline cliff)
Forest (shrub/shoreline cliff)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Open (grass/forbs)
35.6
38.0
28.1
2.5
<1.0
<1.0
5.0
<1.0
18.1
10.4
13.8
32.8
Yes
No
Yes
No
No
No
No
No
No
No
No
Yes
No
Opportunistic
Opportunistic
Telemetry
Opportunistic
Opportunistic
Telemetry
Telemetry
Telemetry
Opportunistic
Opportunistic
Area-const.
Telemetry
Open (grass/forbs)
Forest (branch pile)
Forest (branch pile)
Open (grass/forbs)
Forest (shrub/ravine)
Forest (shrub/ravine)
Forest (shrub/ravine)
Forest (shrub/ravine)
Open (grass/forbs)
Open (grass/forbs)
Forest (herbaceous)
Forest (tidal channel)
12.5
2.5
7.5
69.1
5.8
3.4
<1.0
66.0
5.0
38.8
17.9
No
Yes
Yes
Yes
No
No
No
No
Yes
No
No
No
Frog #432C744D14
Primary active season home range.
• Time -frame: 15-Jun-01 to 1-Oct-01
• Total days: 109
• Observation days: 12
• Greatest home range size: L=71, W=18
Notes:
17-Jul: Early AM visual sighting.
20-Aug: Frog very wet under dry leaves.
Transmitter removed due to belt sores.
30-Sep: Telem. restarted, belt sores 95% healed.
1-Oct: Frog elevated 20 cm on wood (tide out), then
moved to shore. No reception after 1-Oct.
Start
End
Start
End
98
Table G-1 continued.
Date
Key
Frog identification number/Site use type
• Observation time-frame
• Total days within observation time-frame
• Number of days with observations
• Home range, use area length and width (m)
Seasona
Telemetry
Start
and
End
Observation
Type
Strata and Sub-Strata
Season1
Frog
5m
from
Forest/
Open
Edge?
Frog #5028025B2D (Year 2002 data are shaded)
Primary active season home range.
• Time -frame: 26-Aug-01 to 7-Nov-01 & 22-Jul02 to 24-Sep-02
• Total days: Yr 2001 – 74; Yr 2002 - 65
• Observation days: 28
• Greatest home range size (2001): L=80, W=9
Notes:
4-Sep-01: In sub-surface opening under leaves at
bole of sword fern.
10-Sep-01: Off study area, far side of tidal channel.
24-Sep-01: Under dry leaf.
16-Oct-01: Belt sores first noticed.
7-Nov-01: Transmitter removed due to belt sores.
Yr 2001 to 2002 closest distance = 10.7 m.
22-Jul-02: Belt sores well healed. Frog found early
AM (0723) in garden sandy loam pathway that had
been watered the previous day. It moved only 0.4 m
between 0723 and 2019. By dark at 2131 it had
moved 1.0 m further, to a location under a shrub, still
easily visible. It spent the night here.
23-July-02: Frog observed intermittently 0822 to
2146 (dark). Similar short amount of distance
movement as previous day, same habitat conditions.
14-Aug-02: Frog found very wet in dry forest edge
shrubs near watered garden.
18-Aug-02 to 24-Sep-02: All sightings in the garden.
Frog appeared to be utilizing the watered garden area
as a moisture source during this summer.
26-Aug-01
4-Sep-01
10-Sep-01
17-Sep-01
24-Sep-01
1-Oct-01
14-Oct-01
16-Oct-01
19-Oct-01
22-Oct-01
26-Oct-01
27-Oct-01
28-Oct-01
29-Oct-01
30-Oct-01
31-Oct-01
2-Nov-01
3-Nov-01
4-Nov-01
5-Nov-01
7-Nov-01
22-Jul-02
23-Jul-02
14-Aug-02
18-Aug-02
29-Aug-02
11-Sep-02
24-Sep-02
EF
EF
EF
EF
EF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MF
MLS
MLS
MLS
MLS
EF
EF
EF
Start
End
99
Area-const.
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Opportunistic
Opportunistic
Opportunistic
Opportunistic
Opportunistic
Opportunis tic
Opportunistic
Open (shrub)
Forest (shrub)
Forest (shrub/ravine)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Forest (shrub)
Open (garden)
Open (garden)
Forest (shrub)
Open (garden)
Open (garden)
Open (garden)
Open (garden)
36.3
39.4
35.8
2.5
5.9
5.0
3.8
<2.5
3.8
2.5
3.8
0.1-0.2
0.1-0.2
<0.5
<0.5
13.0
<1.0
3.8
est. 4.4
est. 2.5
<2.5
8.1
10.6
3.8
3.8
2.5
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Yes
No
Yes
No
No
No
No
Table G-1 continued.
Key
Frog identification number/Site use type
• Observation time-frame
• Total days within observation time-frame
• Number of days with observations
• Home range, use area length and width (m)
Frog #432D000A12
Use type not known.
• Time -frame: 2-Aug-01
• Total days: 1
Notes: No reception after initial date.
Date
Seasona
2-Aug-01
MLS
7-Oct-00
9-Sep-01
10-Sep-01
17-Sep-01
23-Sep-01
MF
EF
EF
EF
EF
11-Sep-01
12-Sep-01
13-Sep-01
13,14-Sep
15-Sep-01
16-Sep-01
EF
EF
EF
EF
EF
EF
Telemetry
Start
and
End
Start/End
Observation
Type
Strata and Sub-Strata
Dist.
from
Last
Loc.
(m)
Frog
5m
from
Forest/
Open
Edge?
Opportunistic
Open (grass/forbs)
No
Time Search
Opportunistic
Telemetry
Telemetry
Telemetry
Open (grass/forbs)
Open (garden)
Open (grass/forbs)
Forest (shrub)
Forest (shrub)
14.7
7.1
3.8
No
Yes
No
Yes
Yes
Opportunistic
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Open (grass/forbs)
Open (grass/forbs)
Open (grass/forbs)
Open (remnant
Open (grass/forbs)
Open (grass/forbs)
<1.0
5.0
3.8
6.3
<1.0
No
No
No
No
No
No
Frog #425031621F (Year 2000 data shaded)
Possibly migratory stop-over (2001).
• Time -frame: 7-Oct-00 & 9-Sep-01 to 17-Sep-01
• Total days: Yr 2000 - 1; Yr 2001 – 9
• Observation days: 5
• Greatest length and width of use area: L=32,
W=4
Notes:
Yr 2000 to 2001 closest distance = 17.5 m.
23-Sep-01: Transmitter found off, different location
from 17-Sep-01 sighting.
Start
End
Frog #501C750D68
Possible migratory stop-over.
• Time -frame: 11-Sep-01 to 16-Sep-01
• Total days: 6
• Observation days: 6
• Greatest length and width of use area: L=11,
W=3
Notes: Intensive study, see write-up in Chapter 5.
13 to 14-Sep: Evening 13-Sep to mid-day 14-Sep
frog under large old down log.
16-Sep: Last day frog seen, transmitter found off 1Oct at same location.
Start
End
100
Table G-1 continued.
Key
Frog identification number/Site use type
• Observation time-frame
• Total days within observation time-frame
• Number of days with observations
• Home range, use area length and width (m)
Frog #501C6A3723
Not known, likely migratory.
• Time -frame: 22-Sep-01 to 14-Oct-01
• Total days: 23
• Observation days: 7
• Greatest length and width of use area: L=88,
W=2
Notes:
22-Sep: Found in dew-coated grasses, 0755.
1&7-Oct: Poor reception, open/forest vicinity.
14-Oct: At dusk saw and caught frog. Transmitter
removed due to belt sores and poor reception.
Date
Seasona
22-Sep-01
24-Sep-01
25-Sep-01
26-Sep-01
1-Oct-01
7-Oct-01
13-Oct-01
14-Oct-01
EF
EF
MF
MF
MF
MF
MF
MF
1-Oct-01
7-Oct-01
13-Oct-01
16-Oct-01
19-Oct-01
MF
MF
MF
MF
MF
Telemetry
Start
and
End
Start
End
Observation
Type
Strata and Sub-Strata
Dist.
from
Last
Loc.
(m)
•
Frog
5m
from
Forest/
Open
Edge?
•
Opportunistic
Area-const.
Telemetry
Telemetry
Telemetry
Telemetry
Telemetry
Opportunistic
Open (grass/forbs)
Open (grass/forbs)
Open (grass/forbs)
Open (grass/forbs)
?
?
Forest (shrub)
Forest (shrub)
8.1
2.5
est. 1.9
---est. 7.5
34.0
14.5
No
No
No
No
?
?
No
No
Opportunistic
Telemetry
Telemetry
Telemetry
Telemetry
Open (grass/forbs)
Open (remnant
Forest (shrub)
Forest (shrub)
Forest (shrub)
17.6
36.3
6.9
5.3
No
No
No
No
Frog #5006572732
Not known, due to late dates, possibly fall
migratory stop-over.
• Time -frame: 1-Oct-01 to 16-Oct-01
• Total days: 16
• Observation days: 5
• Greatest length and width of use area: L=37,
W=8
Notes:
19-Oct: Transmitter found off, at different location
than 16-Oct observation.
Start
End
101
Table G-1 Continued.
Key
Frog identification number/Site use type
• Observation time-frame
• Total days within observation time-frame
• Number of days with observations
• Home range, use area length and width (m)
Date
Seasona
Telemetry
Start
and
End
Observation
Type
Strata and Sub-Strata
Dist.
from
Last
Loc.
(m)
Frog
5m
from
Forest/
Open
Edge?
Frog #501C792B1E
Fall migration, migratory stop-over, and likely
fall to early winter home range.
• Time -frame: 24-Oct-01 to 12-Dec-01
• Total days: 50
• Observation days: 9
• Observed size for migration route/use area:
L=579, W=2
Notes: 22-Oct had rainfall of 25 mm, largest
rainfall since 22-Aug; this likely triggered
migration to trap.
30,31-Oct: est. location, frog may have already
crossed salt-water cove. Reception difficult.
2-Nov to 7-Dec: 11 days where received
transmission from frog, but could not locate.
12-Dec: Reception from broad vicinity as 29-Nov,
but could not find frog. After this date, no
reception.
24-Oct-01
MF
Start
Trap
Forest (shrub)
26-Oct-01
MF
Telemetry
Forest (shrub)
Frog left primary study area.
27-Oct-01
MF
Telemetry
Forest (shrub/slope to shoreline)
28-Oct-01
MF
Telemetry
Forest (shrub/slope to shoreline)
29-Oct-01
MF
Telemetry
Forest (shrub/slope to shoreline)
30-Oct-01
MF
Telemetry
Forest (shrub/slope to shoreline)
31-Oct-01
MF
Telemetry
Open (remnant forest/shrubs
Frog moved to location across saltwater cove, and to hilltop plateau.
29-Nov-01
LF
Telemetry
Forest (shrub/hill plateau)
12-Dec-01
LF
End
Telemetry
Forest (shrub/hill plateau)
102
17.0
No
No
49.0
0-1
0-1
est. 2
est. 105
No
No
No
No
No
est. 406
?
No
No
Table G-1 Continued.
Key
Frog identification number/Site use type
• Observation time-frame
• Total days within observation time-frame
• Number of days with observations
• Home range, use area length and width (m)
Date
Seasona
Telemetry
Start
and
End
Observation
Type
Strata and Sub-Strata
Dist.
from
Last
Loc.
(m)
Frog
5m
from
Forest/
Open
Edge?
Frog #501C400240
Fall migration, fall migratory stop-over, and late
fall to early winter home range.
• Time -frame: 2-Nov-01 to 29-Dec-01
• Total days: 58
• Observation days: 22
• Greatest length observed for migration route:
L=338 est.
• Greatest length and width observed for
migratory stop-over: L=18,W=2
• Greatest length and width observed for late fall
to early winter home range off-site: L=27,
W=13
Notes:
3-Nov: Frog found in trap adjacent to one it was in
2-Nov. To prevent this happening again, the frog
was moved 7 m from the traps.
5 to 12-Nov: Cold period with only minor
precipitation. The frog made no major moves during
this migratory stop-over.
12 to 18-Nov: Between these dates frog moved to
land across cove and up onto hill. This was
concurrent with the 14-Nov largest rain (61 mm) of
the primary study period (20 Mar to 29 Dec 2001).
29-Dec: Last day frog was seen, reception lost after
this date. Frog may have made major move to a
breeding pond.
2-Nov-01
MF
Start
Trap
Forest (shrub)
No
3-Nov-01
MF
Trap
Forest (shrub)
<1
No
3-Nov-01
MF
(I moved frog)
Forest (shrub)
7.0
No
5-Nov-01
MF
Telemetry
Forest (shrub/near shoreline)
4.0
No
7-Nov-01
MF
Telemetry
Forest (shrub/near shoreline)
2.5
No
11-Nov-01
MF
Telemetry
Forest (shrub/near shoreline)
<1.0
No
12-Nov-01
MF
Telemetry
Forest (shrub/near shoreline)
<1.0
No
Left primary study area by at least 17-Nov and moved to S facing slope on hillside, across the saltwater cove.
18-Nov-01
MF
Telemetry
Forest (shrub/hillside)
est. 297
No
20-Nov-01
MF
Telemetry
Forest (shrub/hillside)
1.0
No
21-Nov-01
MF
Telemetry
Forest (shrub/hillside)
0.5
No
25-Nov-01
MF
Telemetry
Forest (shrub/hillside)
7.0
No
27-Nov-01
MF
Telemetry
Forest (shrub/hillside)
<1.0
No
29-Nov-01
LF
Telemetry
Forest (shrub/hillside)
8.6
No
2-Dec-01
LF
Telemetry
Forest (shrub/hillside)
<1.0
No
4-Dec-01
LF
Telemetry
Forest (shrub/hillside)
1.0
No
7-Dec-01
LF
Telemetry
Forest (shrub/hillside)
7.3
No
12-Dec-01
LF
Telemetry
Forest (shrub/hillside)
2.8
No
14-Dec-01
LF
Telemetry
Forest (shrub/hillside)
<1.0
No
18-Dec-01
LF
Telemetry
Forest (shrub/hillside)
13.6
No
21-Dec-01
EW
Telemetry
Forest (shrub/hillside)
1.8
No
24-Dec-01
EW
Telemetry
Forest (shrub/hillside)
<1.0
No
27-Dec-01
EW
Telemetry
Forest (shrub/hillside)
0.0
No
29-Dec-01
EW
End
Telemetry
Forest (shrub/hillside)
4.0
No
a
Seasons are: Sp, spring = 20 March to 20 June; MLS, mid-through late summer = 9 July to 21 August; EF, early fall = 22 August to 24 September; MF, mid -fall =
25 September to 27 November; LF, late fall = 28 November to 20 December; EW, early winter = 21 to 31 December.
103
APPENDIX H. Behavior descriptions.
Postural, movement, physiological and vocal behaviors observed during this study
and listed in Table 10, are described below.
Postural
There were three observed postures that describe how upright or lateral to the ground
the frog’s body was: sit, crouch and lay.
Sit: frog was the most upright, with head and chest up, angle of body (head to vent)
roughly 45 degrees. This was the common pose seen in a frog that had jumped due to
being disturbed. It was also observed, for example, in video footage (frog 424E56143B)
as the return pose after a feeding lunge, and as the starting pose for subsequent lunges.
Crouch: in this posture, the frog’s torso, including much of the chest, was low to the
ground but its head was up off the ground. This posture was observed only in
undisturbed frogs. It has intermediary body angles between the sit posture, and the lay
posture described below.
Lay: the frog has all ventral surfaces, including head, prostrate to the ground (or
otherwise in a flattened position). This posture was with one exception, found beneath
100% cover. The exception was a video observation of a frog in a flat, linear position
elevated on wood, before the frog made a dive off the wood.
Distance Movement
Hop, walk, dive and climb were the observed movements used by frogs to travel to a
new location.
Hop (or jump): this distance movement, propelled by its legs, typically brings the
frog in an arc, up and out, and then down. Typical distances observed in a hop were 0.1
to 0.5 m (visual estimates). There may be one to many hops in a row. Abundant
observations of hopping frogs occurred during the survey efforts. However, most of
these were of frogs hopping when I approached within 1.0 m. I only observed
undisturbed hopping three times. Of these, one was of a frog leaving the mudflats when
the incoming tidal waters approached within 10 cm. The second was a spring mid-day
observation of a (likely) migratory frog hopping across an open portion of the study area.
104
The third was a video observation where the frog hopped off an elevated location on
down wood, out of the camera view.
Walk: in this movement the frog stayed close to the ground, and moved directionally
forward using all legs. This may be commonly used by frogs, but was less conspicuous
than the hop, and was not observed often. Video footage included two examples of
walking. In one, the frog turned its body and walked out of the video focus area. It was
found 1 ½hrs later, through telemetry, to be 15 cm away. The second example was of a
frog elevated 33 cm on wood. This frog turned its body and then walked ca. 10 cm to the
edge of the wood, where it subsequently made a dive off the wood.
Dive: observed by video as described in the walk description. In this movement the
frog was positioned flat, with its head and forehands perched over the edge of the wood.
Its front legs and head then dropped an estimated 3 to 5 mm, followed 3 sec later by the
frog propelling out and down from the wood.
Climb: only observed while frogs were held within nylon net rectangular traps. The
frogs were able to climb up the sides of the traps.
In-Place Movement
These movements were mostly observed in close-up video observations of frogs in
undisturbed locations. They are classed as head turn (or head upward or downward),
head nodding, feeding lunge, repositioning, body turn, and other minor.
Head Turn (or Head Upward, or Downward): sub-classifications used were: preytracking, other-tracking (e.g., ant and beetle), and unknown. Frogs were observed using a
head turn in response to nearby insect activity as well as for unknown reasons. Examples
include a distinctive head turn toward a prey species that was caught and eaten by the
frog 16 sec later, and a head turn in the direction of an ant that had come near a frog and
was moving away. Head upward was included as a close variation. It occurred alone, or
with a head turn as in the following example: “Head pulls up quickly and to the right 20
degrees. An estimated 12 mm long beetle approached the frog, possibly bumping the
upper chest of the frog before moving away. The frog turned its head in the direction of
the beetle.” Head downward was observed as a movement that in some cases followed
the upward movement.
105
Head Nodding : sub-classifications were With or Post Feeding Lunge, and Other.
Head nodding was movement of the head in an up and down sequence. This was seen in
two variations after prey had been caught. One that followed prey catch (by 3 min 47
sec) was a single event where the frog’s head stretched up until the snout was vertical,
followed by an immediate return of the head to the starting position. In two cases, the
movement was more closely tied to the feeding lunge, one occurring as part of the
retracting portion of the lunge, and the other occurring 5 sec later. These movements
included six and five (respectively) quick movements up and down of the frog’s head.
There were three other occasions where a frog was observed by video to use a similar
movement where prey capture was not involved. These were single sets of head
movement up and down. In all three the movement followed eye retraction.
Feeding Lunge: sub-classifications were successful, not successful, and unknown
(success). In this movement, the frog’s body propelled forward to capture prey, then
recessed back to the near original location, using hind legs like a spring. In one
observation, it appeared that a lunge of less extent occurred with the head and upper torso
primarily stretching forward with a quick motion to capture the prey. Close-up video
footage of one frog showed the frog’s tongue extending out at the peak of the lunge.
Repositioning : the frog changes aspects of its in-place location. An approach that
included movement of the full body involved the frog moving its legs one or two at a
time and putting them in new alignments. Its body may move up and down as this is
occurring, and the frog may end up with a lowered overall height. A different approach
included in this behavior was lowering of the frog’s head and front torso in preparation
for a dive from an elevated location.
Body Turn: this is a major movement by the frog to change body direction. Its use
by the frog may be similar to the head turn. It includes nearly instantaneous moves as
well as slower ones. Examples: “Instant pivot by frog ca. 45 degrees to left, all of body
including legs move.” “Frog quickly (< 1 sec) pivots 45 degrees to the left.” This
occurred when a spider (ca. 15 mm long) was moving under vegetation near the frog’s
posterior end, and likely touched the frog. When the frog changed position, the spider
appeared to be propelled to the surface; it then moved away from the frog. A slower turn
was observed 3 min after the broad turn of a frog’s head and upper torso as follows:
106
“…frog aligns rest of body to same direction as head.” This was a complex movement.
“All legs sequentially moved at least once and the frog’s torso moved upward on
respective sides along with leg movement. Duration 4 sec.”
Other Minor: this included quick flinches, jerks, or slight movements that are not in
other named behaviors. They occurred over small (such as a specific leg) or large
portions of the frog’s body. They represented 29.5% of observed movement behaviors in
the video observations. It is possible that some episodes were in response to an insect
such as a mosquito, landing on the frog, but it was typically not clear as to what caused
the movement. Example: “Six small jerks up and down of body, duration 4 sec.”
Physiological
There were several physiological behaviors or characteristics observed. These
included movement and non- movement types.
Eye Retraction: during this movement I observed the eye to first close, then retract
into the head, re-emerge, and then open. This often occurred in combination with other
movements. The purpose of this beha vior may be (1) to keep the eyes lubricated, (2) to
protect the eyes during movement, and (3) it may additionally be involved in swallowing.
Breathing (throat movement): I observed this but took no data. In an otherwise
motionless frog, throat movement in and out as part of breathing was evident.
Cryptic Coloration: the most observed terrestrial colorations were light brown (e.g.,
the color of dry big leaf maple leaves) during the warm, dry seasons, and dark brown
(e.g., the color of wet big leaf maple leaves) during the cool, wet late fall through early
winter.
Water Absorption, and Evaporative Cooling : As described in the results, I found
evidence that indicated frogs were obtaining moisture through several means in the
terrestrial habitat, and likely the tidal channel associated habitat as well. On warm to hot
days I observed undisturbed frogs in deep crouch positions with most of their ventral
surface adpressed to moist sandy-loam soils. In some observations, the frogs were
glistening moist leading to the likelihood that they were using evaporative processes to
remain cool, by concurrently absorbing moisture from the soil.
107
Vocalization
Distress Calls: the frogs vocalized on occasion when I caught and held them.
Typically the vocalization was a soft chortling sound. On one occasion, a frog made a
loud squeaky scream of ca. 1 sec duration, repeated three times. This frog was near three
other frogs (that may have been a migratory group) leading to the possibility that this call
had a group function.
Male Breeding Call from terrestrial non-breeding location: I heard this only on one
occasion. The call was a soft “cluck, cluck, cluck”. The calling frog was 5.0 m distant
from a second frog. This observation was included in Hayes et al. (2004).
108
APPENDIX I. Conservation Surveys.
During July 2002 I interviewed five scientists regarding northern red-legged frog
conservation in Washington. The persons I interviewed were: Marc Hayes (M.H.),
Washington Department of Fish and Wildlife Research Scientist; Klaus Richter (K.R.),
Senior Ecologist, King County Department of Natural Resources; Kelly McAllister
(K.M.), Regional Wildlife Biologist, Pierce and Thurston Counties; J. Tuesday Serra
Shean (J.S.), Wetland Biologist, WSDOT Environmental Affairs; and, Mike Adams
(M.A.), Research Ecologist, USGS Forest and Rangeland Ecosystem Science Center.
Interviews were held in person with M.H., K.R. and K.M., through written responses
with J.S. and M.A., and included additional written responses from K.R. (I use the
respondents’ names and initials within this appendix. Where used, these should be
considered to be personal communications, 2002, from the respective person.)
The interviews included two components. One part asked for alternatives that would
keep northern red- legged frog populations robust throughout their range in Washington.
Table 14 summarized these responses into a system of components to achieve a robust
population maintenance goal. Part A of this Appendix provides additional detail. The
second part included conservation status related questions. The answers to these
questions are provided in Part B of this Appendix. Cumulatively the interview responses
provide a wealth of insights and information regarding northern red-legged frogs and
their conservation needs.
Part A. System to Achieve Conservation of the Northern Red-Legged Frog
in Washington
1. Research and Monitoring
This component is needed for the development and documentation of demographic,
location, and habitat needs for northern red- legged frogs. This three-piece component is
the hub that provides necessary information to the rest of the system.
a. Geographic presence monitoring linked to high-resolution population
condition index sites. We need monitoring that will enable us to know that frog
populations are remaining robust throughout their range in Washington. The flip side of
109
this is the critical need to know if we have populations in decline and in trouble. Marc
Hayes recommended a two-tiered approach. The first tier is a geographic system that
will tell us where northern red- legged frogs are. We have general range maps (Dvornich
et al. 1997, Leonard et al. 1993) but these do not provide the specificity to tell us where
protection measures are needed or where populations may have problems. For this, finer
resolution such as the atlas documentation for portions of King County (Richter and
Ostergaard 1999), and the inventory of U.S. Navy lands on the Kitsap and Toandos
Peninsulas (Adams et al. 1999) is needed. Broad presence information needs to be linked
with the second tier, high resolution population monitoring, to tell us about population
condition. Monitoring of egg mass numbers is the most direct approach to observe
population condition.
b. Demographic and habitat research (including relationships with exotic
species). A scarcity of basic demographic and habitat use data for these frogs in
Washington exists, and detailed demographic and habitat studies are needed.
Adams (1999, 2000) researched the relationship between northern red-legged frog
abundance and presence in wetlands, with wetland habitat, water permanence, and
presence of exotic species (bullfrogs and fish). At Fort Lewis, in Pierce County
Washington, he found negative survival effects from exotic species. However, other
untested factors associated with pond permanence were more important for low survival
of northern red- legged frog larvae (Adams 2000).
c. Landscape level analysis for rapidly developing areas. Klaus Richter is
accomplishing research to understand native amphibian protection needs for rapidly
developing areas of King County. This includes a GIS-based system to evaluate habitat
availability for each life history stage of amphibian species present. These habitats cover
oviposition sites with the correct water depth, velocity and hydrology; larval habitat
(including stable hydrology); metamorph habitat (transitional habitat around the
perimeter of larval waters where small, easily desiccated animals can remain until large
rains wet the upland habitat and provide opportunity for dispersal); juvenile habitat; and
adult habitat. The latter two habitats can be spatially separated by considerable distances
and necessitate secure movement pathways between each. This system is being “truthed”
by evaluating characteristics of locations where amphibian species have been lost. The
110
evaluation looks at the core wetland or lake buffer zone and a larger 1,000 m radius for
amount and patterns of development, and vegetation characteristics. The evaluation will
provide information on characteristics of development that cause loss of amphibian
species diversity.
2. Protection for Northern Red-Legged Frogs in Rapidly Developing Areas
Protective focus is a critical need for areas in the path of development. This
component has four parts.
a. Habitat needs. Normal hydrology is needed for northern red- legged frog egg
survival. To provide adequate protection for hydrology of the wetlands systems, 65% of
the basin affecting hydrology of the wetland needs to be left in forest/native vegetation,
and < 10% of the developed portion should be in impervious surfaces (K.R.). Similarly
Kelly McAllister recommends a mosaic of forest and wetlands with some openings,
breeding habitat with benefits from warm water conditions, forest area that retains
moisture for adults, floodplains maintained in natural vegetation, and allowance for
beaver activity that floods areas, kills trees and allows light to get in. In addition,
preserving and protecting intact connected aquatic habitat with high cover and
complexity are needed (J.S.).
b. Determination of and protection of population core zones. This system is
being developed by Klaus Richter to provide a science-based framework for species
protection. Wetland systems in areas that will be developed are evaluated to determine
likely locations for amphibian population core zones. Mapped wetlands are evaluated
with 200 m buffers, and 1000 m wide habitat zones necessary for juvenile and adult life
history stages. Through this approach, overlapping wetland and habitat zones can be
seen, and areas likely to be population core zones are determined and can become a focus
for protection.
c. Protection of ephemeral wetlands. Ephemeral wetlands need focus for two
reasons. First, they have been disproportionately lost, and second, northern red- legged
frog larval survival is typically less in permanent wetlands (Adams 1999, 2000). Loss of
shallow wetlands needs to be mitigated by creating shallow wetlands, instead of replacing
shallow wetlands with deep ones (M.A.).
111
d. Special protective measures for amphibian use of stormwater ponds.
Ostergaard (2001) provides recommendations for making stormwater ponds amphibian
friendly. She found that the ponds attract amphibians and if characteristics lead to good
egg and larval survival they may be source areas. However, without consideration of
amphibian needs, they may be population sinks. She recommends: site stormwater ponds
within 2 km of each other and with adjacency and connectivity to forest, other open
space, or protected areas to provide for re-colonization of ponds over time; discouraging
amphibian use by locating ponds away from retained natural areas if water quality is
expected to be poor; cleaning ponds late summer to fall when amphibian use is low, and
cleaning only ½of a pond to retain habitat; designing ponds to dry in late summer to
prevent colonization by bullfrogs; and posting signs at ponds explaining protection needs
for amphibians.
3. Education
Most survey respondents specifically identified education as important for
achievement of the population goal. The following inclusions were recommended:
volunteer egg mass surveys, education that makes frogs an important part of children’s
experiences, a flyer/brochure for how to promote frogs in your backyard, news stories
and other media opportunities regarding frogs and including the importance of beavers in
maintaining diverse aquatic habitat.
4. State Conservation Status
This component has two parts.
a. Inclusion in Washington’s conservation status categories as a “monitor”
species. Northern red- legged frogs were previously a state priority species, but they
currently have no state status. This is due to being relatively common, along with limited
resource availability for other species with definitive risk. In addition, local government
critical area ordinances (CAOs) use a rating system to determine buffer width. If priority
species are present, maximum buffer widths are required. Previously northern red- legged
frogs triggered maximum widths for a vast majority of wetlands although it had not been
intended for a relatively common species to trigger the maximum buffer width (K.M.).
In light of this history, but taking into account population vulnerabilities for northern red-
112
legged frogs, at a minimum, inclusion in the state’s “monitor” status is appropriate. This
status makes the species a priority for inclusion in the state’s data collection and mapping
system.
b. Include regionally-based conservation needs in the state conservation system.
The northern red-legged frog is a species that regionally (e.g., much of the Puget
Lowlands) could become extirpated while frog populations in coastal areas remain
healthy. The current conservation status system for Washington provides one statewide
status and does not differentiate threats between regions. Updating this system to include
ecoregion or basin level focus is needed. Oregon is an example of a state that has such a
system. Oregon includes smaller land units in its listing approach and is therefore better
able to define areas of concern for northern red- legged frog populations (Oregon
Department of Fish and Wildlife 1997).
5. Bullfrogs and Exotic Fish
Based on Adams (1999, 2000) bullfrogs and exotic fish have negative effects on
northern red-legged frog survival, however other poorly understood factors appear more
important. Thus, bullfrogs and exotic fish should be reduced, but this should not lessen
attention to other components. Suggestions include preventing the spread of non- native
fish, and, possibly removing fish from some wetlands to create a mosaic of fishless
habitat (M.A.) and, maintaining bullfrog- free wetlands (J.S.). Adaptive management may
allow refining this approach and focusing on selected exotic fish that appear to be of
greater concern for northern red- legged frogs and other amphibians (M.H.).
6. Adaptive Management
The primary purpose of adaptive management in this system is to assure that measures
being taken to achieve long-term protection for the frogs are succeeding. To accomplish
this, data and new information must be gathered and must be adjusted as necessary.
Opportunities, Barriers (i.e., Obstacles), Resources, Potential Harms, and
Uncertainties Related to Implementation of Alternatives
I asked questions related to feasibility and challenges associated with implementation
of conservation measures. This is a summary of the responses.
113
Opportunities exist for implementation of the alternatives through best available
science use as required by the state Growth Management Act, tax relief for preserving
wetland buffers larger than required, the greater protection afforded to federal lands,
allowing beavers to create habitat, timing water fluctuations with amphibian
requirements, controlling/confining bullfrog populations (e.g., by allowing waters to dry
out in the summer), and, preventing the spread of invasive species or anything that will
decrease habitat diversity and complexity.
Barriers identified include cost and lack of funds (e.g., King County has eliminated
funding for the amphibian monitoring program), pressure to lessen existing buffer
protection for wetlands and to not take property “rights” away from people, urbanization,
exotic species, and beavers being considered a nuisance.
Resources for implementation include interest, money, information, and county weed
boards.
Potential harms and uncertainties noted were that management for one species may
discriminate against other species.
Part B. Conservation Questions and Responses
1. What do we or don’t we know about northern red-legged frog populations in
Washington?
M.H. GAP Analysis (Dvornich et al. 1997) gives us a general idea. From this we
know that the northern red- legged frogs are at the low elevations. It doesn’t tell us where
there are problems. We think the problems are where there is development. Overall at
the geographic level we know very little. The King County study by Klaus Richter and
the Fort Lewis study by Mike Adams are the only geographic studies. We need a system
that can both detect the frogs and tell you about the population condition. Areas with low
population densities will be difficult to have detection and will be prone to type II errors
(i.e., assuming they are not the re when they are). Coastal systems are the stronghold for
this species. This is the same in California as well. No populations have been studied
demographically in Washington. The only studies are small pieces, mostly of movement.
These pieces do not yet provide predictive ability for habitat needs. In southwestern
Oregon, there are 5 years of data for the Umpqua.
114
K.R. Very little. We could infer knowledge from habitat relationships but atlas data
is missing, and beyond that we know even less about populations (trends, age/gender
ratio, habitat use, etc.).
K.M. This species is still common and present throughout where its home range is
thought to be. It has been extirpated from major urban areas such as Seattle and Tacoma.
We are in the heart of the range for this species, and they seem fairly resilient. The
biggest challenge is in the developing lowlands.
2. What are sources of mortality to the frogs (embryo, larval, metamorph,
juvenile, adult)?
M.H. Embryonic mortality is usually minimal e.g., if there is > 3% mortality to egg
masses this is a concern. This is due to the early timing of breeding, which corresponds
with few predators being out. Leeches will take a few embryos. The biggest problem is
Saprolegnia (water mold) which is associa ted with UVB (ultraviolet-B light). Ninety
percent of mortality occurs during the larval and metamorph life stages. Larval mortality
is rarely < 70%. Of the invertebrates, larval diving beetles and dragonflies are the biggest
predators of the tadpoles and metamorphs, followed by backswimmers and other
invertebrates such as water scorpions. Of the vertebrates, common garter snakes (they
have 95% of their diet from still-water amphibians) are important. These snakes are the
major predator of the metamorph stage. Wading birds such as the great blue heron and
green-backed heron can be locally important predators. For frogs older than one year,
garter snakes are still an important predator. They will take even large frogs (e.g., Shean
2002, includes an observation of an 80 mm telemetered female frog within a snake).
Raccoons are known to take leopard frogs, and might be predators for northern redlegged frogs. Klaus Richter has observed a mink taking a northern red- legged frog.
Mink have been found in Oregon to have a winter diet that includes Oregon spotted and
bull frogs (1/3 of bones in scat were from these species). Also, a road-kill otter in
Oregon was found to have six adult red- legged frogs in its stomach. Both felids and dogs
avoid amphibians. Road kill is an issue but is difficult to assess.
K.R. In urbanizing areas we have habitat fragmentation, hydrological changes
associated with impervious surfaces etc. This causes loss of depth and duration of water,
115
invasion of exotics and aggressive natives, and bullfrog and other exotic introductions.
In rural areas and farmlands we have water quality, bullfrogs, sunfish, bass and others.
K.M. Juveniles are a favorite food of the common garter snake and northwest
salamander larvae. Common garter snakes, great blue herons, river otter, and mink eat
adult frogs. It is not known how significant road kill is, but it must be if it is a busy road.
UV effects are unknown for northern red- legged frogs.
M.A. I think that fish introductions and habitat changes (shift from shallow,
ephemeral to deep permanent) habitats are the two biggest factors that we know about.
Bullfrogs don’t seem to be a big factor in Washington. We don’t know anything about
upland habitats. We see some evidence that road density has a negative association with
red-legged frogs in Oregon.
3. Have northern red-legged frog declines been observed in some areas?
M.H. Not aware of decline data for Washington. Willamette Valley Oregon, yes.
K.R. Yes, but other areas we know little about.
K.M. Only on a coarse scale: Seattle, Tacoma, and for Olympia they are at the
outskirts in Watershed Park.
M.A. They have certainly lost habitat but status and trends aren’t well known.
4. What are thresholds of concern for population decline?
M.H. These are unknown.
K.M. First what will happen is that people who have been working in wetlands and
streams will note that they don’t see frogs any more. It would be good if broad
amphibian monitoring was occurring, but lacking this we will need to rely on peoples’
observations. This would be the first sign of decline. This would then start a more
formal effort to assess the concern. This approach is not as good as a long-term program.
For some frog species (e.g., back east) call routes can be driven. This species is much
more difficult to survey because it does not have a loud call. People must go out in the
wetlands for this species.
116
5. What are thresholds of concern for habitat loss in the range of the frog?
M.H. We know development is a problem, but what degree of development is a
problem is unknown.
K.M. We need to be able to define what habitat loss is. We don’t know this yet.
Asphalt would be clear habitat loss, but there are many degrees of loss and we don’t
know which are important.
J.S. At the microhabitat scale they need at least 50% cover based on Thurston
County data.
6. Do we have a monitoring system in place that includes this species?
M.H. For Thurston County a beginning of a monitoring system is in place. There are
a few scattered efforts with egg mass surveys. These are community based.
K.R. No. A 9-year program for King County was terminated this year.
K.M. No, we are relying on common knowledge. (See #4 above.)
M.A. Not that I know of.
7. How are conservation rules set up at the state and local level?
K.M. At the state level candidate and monitor lists are updated yearly. Biologists
with WDFW submit new information to the state endangered species program for species
that should be on these lists, or where data shows they can be removed. Other persons
can also petition WDFW similarly, with species information. Candidate lists are
prioritized for species most in need of listing. A status report is done. This goes to the
Fish and Wildlife Commission, and a public review is held for recommended listing
decisions. The monitor list drives data entry, and is considered a scientific basis of
information. Federal Habitat Conservation Plans (HCPs) have value for this species.
The DNR HCP is good for frogs by leaving more trees, and providing for more down
logs, and decaying wood. Both the City of Seattle (for water supply system watersheds)
and the USFS have mandates for biological diversity. These efforts provide midelevation protection for northern red- legged frogs. The biggest challenge is in the
developing lowlands. In these areas for Pierce and Thurston Counties, typically
developers leave more than the minimum protection required. This hasn’t tested how
well the local protection ordinances protect these species. There are important initiatives
117
occurring in the state. One is the ecosystems project. This is a GIS-based analysis of the
locations in the state of important habitats and species. In theory this can be used for
regulatory preservation.
K.R. No teeth.
8. Are our conservation rules geared towards thinking about species needing
different habitats at different times, and migration routes?
M.H. Poorly, a general view is that amphibians don’t need much space. On a spatial
scale, red- legged frogs use a larger space.
J.S. Previous thoughts had been that red- legged frogs leave the wetland immediately
after breeding. This was not true in my Thurston County study. Emergent and forested
wetlands were important; scrub-shrub was used transitionally.
K.R., K.M. No.
9. Should the northern red-legged frog in Washington have a specific
conservation status?
M.H. Yes, but with a regional qualifier, based on degree of development.
K.R. We don’t have enough information on this species. During listing discussions 5
years ago we didn’t feel that they were disappearing or decreasing in numbers. There are
regional vs local concerns. In a system built for statewide concerns, when do you list
based on local concerns?
10. Can the species conservation management system be proactive?
M.H. Yes. But to do so we need a geographic level system to tell us where the frogs
are, linked with a higher scale inventory to tell us about population condition.
K.R. No. We need a landscape approach that protects ecosystem structure and
function utilizing principles of conservation biology, landscape ecology and population
biology. The current high cost situation with salmon (re ESA) shows that we had a false
economy. We have the same false economy with amphibians.
J.S. We need to create land and wildlife management standards that include
amphibians. They are often overlooked as important components of ecosystems.
118
11. What will allow people to care?
M.H. Education at a variety of levels. Ownership in a process and the ability to
influence. Two levels of needing to care are: (1) non-altruistic where frogs are an
indicator of habitat quality for frogs and for people; and, (2) intrinsic, where people have
a general respect for the natural system.
K.R. Ability to make money. If it doesn’t cost financially or entail personal
sacrifice.
K.M. People are diverse, some will care and some won’t. Education is very
important, especially while people are young. Children in an urban setting have a hard
time getting to understand nature’s importance. We have to find a way to make sure
frogs are a part of children’s experience. News stories are also an opportunity.
J.S. Education about amphibians in general, and about northern red- legged frogs and
their habitat requirements will encourage people to have the desire to help preserve this
species.
119
