Investigating Habitat Loss as a Causal Factor in Western Toad (Bufo Boreas) Decline in the Lowland Puget Sound Ecoregion Using Field Surveys and GIS Analysis

Item

Title
Investigating Habitat Loss as a Causal Factor in Western Toad (Bufo Boreas) Decline in the Lowland Puget Sound Ecoregion Using Field Surveys and GIS Analysis
Date
2004
Creator
Freed, Sanders B.
Identifier
Thesis_MES_2004_FreedS
extracted text
INVESTIGATING HABITAT LOSS AS A CAUSAL FACTOR IN
WESTERN TOAD (Bufo boreas) DECLINE IN THE LOWLAND PUGET
SOUND ECOREGION USING FIELD SURVEYS AND GIS ANALYSIS

by
Sanders B. Freed

A Thesis: Essay of Distinction
Submitted in partial fulfillment
of the requirements for the de~ee
Master of Environmental Studies
The Evergreen State College
June 2004

1

This Thesis for the Master of Environmental Studies Degree

by
Sanders B Freed

has been approved for
The Evergreen State College

by

(.

Gerardo Chin-Leo
Member of the Faculty

June 30th 2004

11

ABSTRACT
Investigating Habitat Loss as a Causal Factor in Western Toad
(Bufo boreas) Decline in the Lowland Puget Sound Ecoregion
Using Field Surveys and GIS Analysis
Sanders B Freed

The western toad (Bufo boreas) was once a common inhabitant of the western
U.S. Multiple causal factors (i.e. habitat loss/degradation, chemical
contamination, UV-8 radiation and global warming, invasive species, and
pathogens) have lead to population decline throughout the known historical range
of the species, resulting in federally ''threatened" status in several western states,
and the listing as a "species of concern" in Washington State. In the lowland
Puget Sound ecoregion, population decline is suspected, although the severity and
causes of decline have not been investigated. Using field surveys of known
historical populations, and GIS analysis of land cover within population home
ranges, regional decline was assessed and habitat loss was investigated as a causal
factor. Twenty-five sites were monitored for presence/absence of Bufo boreas.
Results of the field surveys revealed population decline ranging from 35-56%,
depending on metapopulation sink site inclusion. Land conversion within the
Bufo boreas home range, as determined by the literature, was evaluated and
categorized as agricultural, residential, and industrial. GIS analysis results
revealed a general trend towards Bufo boreas presence at sites of limited
development. Industrial and residential development at sites of Bufo boreas
presence never exceeded 4% of the home range, suggesting a threshold of
development compatible with Bufo boreas presence. Metapopulation structure
was another population dynamic revealed by the results of this investigation.
Source population dispersal to sink sites was evident in the GIS analysis. In
conclusion, Bufo boreas has experienced significant decline of known historical
populations, which is like!y the ~esu~t ofhabita~ l?ss/degrad~tion.. Thus, Bufo
boreas requires conservation action if the remammg populations m the lowland
Puget Sound ecoregion are to persist.

TABLE OF CONTENTS
TITLE PAGE.
APPROVAL .

ii

TABLE OF CONTENTS

iii

TABLES AND FIGURES

IV

ACKNOWLEDGEMENTS .

V

I. INTRODUCTION .

1

II. METHODOLOGY

3

Ill. WESTERN TOAD NATURAL HISTORY

5

IV. WESTERN TOAD STATUS

10

V. CAUSAL FACTORS IN WESTERN TOAD DECLINE

13

A. Habitat Loss I Degradation

14

B. Chemical Contamination .

15

C. Climate Change and UV-8 Radiation

18

D. Invasive/ Introduced Species

22

E. Pathogens .

23

VI. RESULTS

24

VII. DISCUSSION

26

VIII. CONCLUSION.

36

REFERENCES

38

TABLES

48

FIGURES

51

ll1

LIST OFTABLES
TABLE I: FIELD SURVEY RESULTS

48

TABLE 2: LAND USE ANALYSIS RESULTS

50

LIST OF FIGURES
FIGURE 1: SITE LAND USE COMPARISON

51

FIGURE 2: ALL SITES DEVELOPMENT COMPARISON

52

FIGURE 3: PRESENCE: LAND USE COMPARISON

53

FIGURE 4: ABSENCE LAND USE COMPARISON

53

FIGURE 5: LAND USE (MODIFIED)

54

FIGURE 6: INDUSTRIAL AND RESIDENTIAL DEVELOPMENT
(MODIFIED) .

54

FIGURE 7: SURVEY SITES.

55

FIGURE 8: FORT LEWIS SITES

.

56

FIGURE 9: T ARBOO CREEK

57

FIGURE 10: LAKE ST. CLAIR

58

FIGURE 11: CROCKER LAKE

59

FIGURE 12: WYE & KOENAMAN LAKE .

60

FIGURE 13: NISQUALL Y LAKE

61

FIGURE 14: ANDERSON LAKE

62

FIGURE 15: OAK PATCH LAKE

63

FIGURE 16: FAGAN & McENNIERY LAKE

64

FIGURE 17: RANGER LAKE

65

FIGURE 18: BEAVER LAKE

66

FIGURE 19: CARSON LAKE

67

FIGURE 20: BEAR & PORTER CREEK

.

68

FIGURE 21: OUR LAKE

69

FIGURE 22: ECHO LAKE

70

iv

ACKNOWLEDGEMENTS
I would first like to thank Gerardo Chin-Leo for being my reader. I would
also like to thank Lisa Hallock, Lori Salzer, and Kelly McAllister for their
professional input and assistance. I'm indebted to Michael Thoma and Mike
Brown for their help with the GIS portion of this thesis. Many thanks to Pat Dunn
of The Nature Conservancy for his patience at work during this undertaking and
for the time he allowed me on his computer. Thanks to Ron Pratt for allowing me
to use his kayak for field surveys, and again to Mike Brown for accompanying me
on occasion. Additional thanks go out to Jim Lynch for the assistance with field
surveys on Fort Lewis and for the good conversations about the western toad.
Eric Delvin also deserves thanks for lending me office keys at all hours of the day
and night. Thanks to Kirsten Freed and Kate Hardin for their time and valuable
edits. My mom, Judy Freed, also deserves thanks for her support. Lastly, I would
like to thank my dad, Mike Freed, for encouraging my education and inspiring
appreciation for the environment and all that it supports.

V

I.

Introduction
Worldwide amphibian de 1· h be
.
.
.
c me as come the subJect of mcreasmg attention,

controversy and research (Lips 1999; Houlahan et al. 2000; Wake 1991;
Pechmann and Wilbur 1994). Multiple hypotheses have been proposed as causal
factors in the declines, including habitat loss/degradation (Davidson et al. 2001 ),
UV-B radiation (Blaustein et al. 1994a), non-native predators (Knapp and
Mathews 2000), climate change (Lips 1999), pathogens (Berger et al. 1998;
Kiesecker et al. 2001 b), and chemical contamination (Ankley et al. 1998). Each
factor has been linked to individual cases, however, there is no evidence of a
single cause for all of the declines (Blaustein and Wake 1990). In fact, there is
increasing evidence that in many cases several factors may be acting
synergistically to cause the declines (Carey 1993). Because of their complex life
cycle, which encompasses both terrestrial and aquatic stages, and highly
permeable skin, amphibians are considered "bio-indicators" of environmental
integrity (Stebbins and Cohen 1995). As bio-indicators, amphibian declines,
especially those directly traceable to anthropogenic causes, could indicate the
overall deterioration of ecosystems and the likelihood of future extinctions of
non-amphibian species (Parsons 1989).
The western toad (Bufo boreas) was once considered a ubiquitous species in
western North America (Stebbins 1985). Prior to declines, it was not uncommon
to see thousands of toadlets migrating from breeding sites or to witness
spectacular breeding aggregations involving hundreds of adult toads. Within the
past fifty years, the western toad has suffered drastic population declines

1

throughout its range ( Drost and Fellers 1996; Stebbins and Cohen 1995;
st
Blau ein et al. 1994b; Carey 1993), which has lead to its threatened status in
several regions (Federal Register 1991 ), and to its listing as a "species of concern"
in Washington State (WDFW 2003). The family Bufonidae, to which the western
toad belongs, is the most imperiled family of anurans in the New World tropics,
with a total of 18% of known species to be in decline (Semlitsch 2003).
Difficulty in establishing decline plagues amphibian conservation efforts, and is
often due to lacking and incomplete historical information on abundance and
distribution, which would allow meaningful comparisons with the present (Fisher
and Shaffer 1996). This is the current situation regarding the western toad in
Washington State; although decline is suspected it is difficult to verify. The
Washington Department of Fish and Wildlife (WDFW) has a database of
historical sightings that can be used to evaluate decline by conducting a
presence/absence inventory. If decline is confirmed, as defined by a reduction in
breeding aggregations/ populations, then habitat loss/degradation can be
investigated as a causal factor in the decline of the western toad (Bufo boreas)
using GIS analysis of land use.
Investigating habitat loss/degradation is a logical first step in assigning cause
in the decline of any organism. Direct human impacts, such as habitat alteration,
are the most easily identified and quantified. In the case of the western toad,
habitat Joss must be considered before directing research towards the many other
causal factors attributed to declines. If habitat loss/degradation is responsible for
the suspected decline of the western toad in Washington, a negative relationship

2

should exi

st

between the amount of land altered within the western toad home

range and the likelihood of persisting, viable breeding populations.
The first step in evaluating habitat loss as a causal factor in western toad
decline was to determine the severity of decline, which was accomplished by
using the WDFW historical sightings database to assess historical distribution.
This was followed by field surveys to assess current distribution. The second step
was to determine habitat loss at each site using GIS analysis of land cover to
elucidate the relationship between habitat loss and population persistence. The
results of this investigation provide a useful foundation that can be used to gain
insight into and evaluate the decline of the western toad in western Washington,
develop conservation strategies to ensure population persistence, and direct
further research.

II.

Methodology
This paper is essentially an evaluation of western toad (Bufo boreas) decline

in the lowland Puget Sound ecoregion and an investigation of one causal factor:
habitat loss. Using the Washington Department of Fish and Wildlife historical
sightings database, water bodies used as breeding sites where populations of
western toads have been reported as far back as 1985, were inventoried to assess
presence or absence of populations. Presence was assessed by visual sightings of
breeding aggregations, egg strings, or tadpoles. Once presence or absence was
confirmed,

o IS analysis of sites was used to determine if breeding populations are

more likely to occur with decreasing percentage of home range development.

3

The WDFW hi t · al ·gh ·
s one SI tings database contained 177 entries, 25 of which
met the criteria of possible breeding sites since 1985 Thi .
t· ti.
.
s1nves1ga on
arbitrarily chose the year 1985 b

ecause

th

c.



·

e 1ocus was aimed at determming recent

decline. Given the number and distribution of all 177 sightings contained in the
database, historical decline has been much more severe than the recent decline
considered in this study. Sites included in this study had historical records
mentioning large numbers of toads, indicating a breeding aggregation; multiple
sightings at a single location, signifying a population in close proximity; or eggs
or tadpoles, indicating a breeding site.
Field surveying of sites began in late March, coinciding with breeding
aggregations. Surveying began at lower elevations and progressed to higher
elevations in an attempt to witness breeding aggregations: the most conspicuous
way to assess presence. Surveying was accomplished by several means, including
wading, kayaking, and canoeing water bodies where breeding occurs. Wading
was generally the most reliable means, enabling a thorough assessment of the
entire water body. Presence was assessed by visual confirmation of individuals,
egg strings, or audible vocalization. Breeding aggregations were generally
consumed by the task at hand and fairly conspicuous.
Upon completion of field surveys, results were entered into a GIS program
and overlayed on a land cover raster data set that was written by the Washington
Department of Natural Resources under the Natural Heritage Program in 1999.
Land cover was assessed in each 30 square meter block of the data set and
categorized. As determined by the literature, each field-surveyed site was then

4

buffered by 2.3 km, representing the home range of the western toad. Land use
categorized as m
· d ustrt·a,
I res1·dentI·a1 , and agncultural
·
was assessed within each
buffer. At each site, percentages of the various land use types, as well as the total
development within each buffer was determined, graphed, and analyzed.
Materials utilized included: the Washington Department of Fish and Wildlife
historical sightings database; peer-reviewed literature; books addressing
amphibian biology, natural history and conservation; GIS software (ArcMap); and
land cover raster data written for the Natural Heritage Program by the Washington
Department of Natural Resources.

III.

Western Toad Natural History
Understanding an organism's natural history is an essential prerequisite to any

management or conservation attempt. Western toads (Bufo boreas) exhibit a
typical biphasic life cycle that involves both aquatic and terrestrial life stages.
Adult toads, which require 4-6 years to reach sexual maturity (Carey 1978),
synchronously aggregate at small breeding sites in early spring, generally from
April to May (depending on elevation and regional considerations). These
aggregations often contain several hundred individuals (Marco et al. 1998),
although Nussbaum et al. (1983) recorded over 5000 individuals in a single
population. Sex ratios in western toad populations are usually disproportionately
skewed towards males. Campbell (1970) had a sex ratio of73% male to 27%
female in all populations studied. Western toads may move long distances to
breeding sites and utilize the same reliable sites year after year (Nussbaum et al.

5

1983). Breeding site fidelity is attributed to the well-developed olfactory capacity
used in homing behavior (Tracy and Dole 1969).
Muths (2003) studied home range and movement in undisturbed habitat in
boreal toads (Bufo boreas boreas) and found the maximum distance traveled in
her study was 2.3 km, although males in her study traveled significantly lesser
distances. On average, females traveled 2.4X the distance of males and had 4X
larger home ranges. These results were supported by the results of Bartelt (2000),
suggesting these distances are representative of the species. Larger home ranges
in female toads probably leads to greater mortality, especially in the lowland
Puget Sound ecoregion, due to the increased probability of moving into altered or
~eveloped habitat and the concurrent increase in predation risk. Clearly, this
could also have repercussions for population level fecundity.
Upon arrival at breeding sites, western toads are explosive breeders and males
exhibit scramble competition for mates (Olson et al. 1986). Communal breeding,
communal oviposition, and explosive breeding are believed to reduce predation
risks of adult anurans (Kagarise Sherman 1980). This belief is supported by the
results of Olson (1989), where predation on toads by ravens (Corvus corax) did
not increase proportionately with size of breeding aggregation. The mating period
is short (4-6 nights) and males do not produce advertisement calls (Marco et al.
1998). Instead, males rest quietly in the water and swim vigorously towards
movement. Upon reaching another toad or similar artificial mate, males exhibit a
strong clasping response. Male toads give a bird-like twittering call (release call)
in response to amplexus by other males (Nussbaum et al. 1983), although

6

Campbell (1970) suggests this vocalization may also serve to attract other
conspecifics to a specific area of the breeding site. Amplexus with females is
tenacious and prolonged. Females lay eggs in long intertwined strings at a depth
of 5-10 cm (O'Hara 1981), and generally are fairly conspicuous and easily
detected (Blaustein et al. 1994). An average spawn produces 12,000 eggs
(Blaustein et al. 1994b; Samollow 1980). After egg laying, females quickly leave
the breeding site (Marco et al. 1998).
Egg development takes 3 to 13 days (Corn 1998; Leonard et al. 1993),
depending on temperature. Upon hatching, western toad tadpoles commonly form
large schools, which scavenge and feed upon algae and organic detritus, growing
to approximately l inch in length. Western toad tadpoles contain bufotoxins in
their skin, making them unpalatable to many predators (Brodie 1987). Predators
that swallow tadpoles whole, or insects that pierce and suck body fluids, are less
deterred by the chemical defenses than those predators that bite, masticate, or
taste the tadpoles (Peterson and Blaustein 1992). Salamanders, frogs, birds, garter
snakes, and aquatic invertebrates are common predators of larval (tadpole)
western toads (Arnold and Wassersug 1978), although roughskin newts (Taricha
granulosa) and rainbow trout ( Oncorhynchus mykiss), two co-occurring predators,
find western toad tadpoles unpalatable (Peterson and Blaustein 1991 ).
Many studies have investigated the response of tadpoles to predation and
chemical alarm cues (Chivers et al. 1999; K.iesecker et al. 1996; Hews 1988).
Hews ( 1998) found that tadpoles increased their activity and avoided areas where
conspecifics were being eaten. This alann response reduced the capture

7

efficiency of predators. K.iesecker et al. (1996) found that western toad tadpoles
can recognize predators using chemical cues, resulting in decreased movement,
avoidance of predator compartmen~ and an increase in shelter use. This ability to
chemically detect predators and alter behavior in response increases larval
survivorship and provides tadpoles with critical information at night, in turbid
water, and in highly structured environments. Congruently, Chivers et al. (1999)
demonstrated that tadpoles raised in the presence of chemical cues of predators
and injured conspecifics metamorphosed in significantly shorter time than
tadpoles raised in benign environments. This shift in life history may reduce
exposure to aquatic predators, although it may have consequences for fitness if
metamorphs emerge a~ a reduced size.
Multiple studies have shown that adult body size is positively correlated with
female fecundity, male mating success, physical performance, and resistance to
starvation (Davies and Halliday 1977; Lillywhite et al. 1973). Indeed, Goater
( 1994) found evidence that larval toads, when reared at low densities, were
significantly larger at metamorphosis and emerged earlier. This may positively
affect reproductive success by directly affecting adult life history traits or by
indirectly affecting fitness related characteristics. Examples of the benefits of
large size at metamorphosis include both increased adult size and early time to
first reproduction (Pecbmann 1994; Semlitsch et al. 1988; Smith 1987).
Therefore, high larval mortality may not necessarily result in population level
reductions in fitness and persistence.

8

Tadpoles develop in 30-45 days depending on temperature, density, food
supply and regional differences. The juvenile (toadlet) stage in western toad
development is subject to tremendous mortality rates (Stebbins 1962). This is
expected because it is the toadlets' first experience with terrestrial habitats.
Clarke ( 1977) averaged all information available on toad metamorph and juvenile
survival, arriving at a 20% annual survival rate. Nussbaum (1983) concluded that
mortality to reproductive age must be well over 99%. Although western toads do
contain bufotoxins, they still suffer high mortality from frog and garter snake
predation after metamorphosis (Pearl and Hayes 2002). Belden et al. (2000) found
that juvenile western toads avoided chemical cues of snakes fed juvenile
conspecifics, but did not avoid snakes fed larval conspecifics. This behavior may
have advantages, as it reduces the amount of time responding to alarm, and
increases the time allowed for foraging. After dispersal from the breeding site,
little information is available on western toads until they return to breeding sites
after reaching sexual maturity (Muths 2003).
The importance of thermoregulation in western toad behavior seems to be
critical in all aspects of its terrestrial ecology. Smits (1984) studied microhabitat
use in toads over the course of a year, finding predictable seasonal and daily
activity related to a relatively narrow range of acceptable temperatures. The study
also noted the importance of burrows in thermal buffering and anuran ecology.
Hailman (1984) found that western toads exhibit a nocturnal bimodal activity
pattern that coincides with ambient illumination. This study and others (Campbell

J970) suggest this activity pattern derived from illumination is important in

9

foraging success. Muths and Com ( 1997) have documented basking behavior by
adult and juvenile western toads in the late summer after the breeding season.
The authors speculate the behavior may serve multiple beneficial purposes,
including increased rates of spermatogenesis, enhanced functioning of the
immune system, and increased rates of digestion and growth. Lillywhite et al.
( 1973) studied behavioral thermoregulation in juvenile western toads and
concluded that the western toad has evolved a thermoregulatory mechanism,
which maximizes growth and economic utilization of energy. Energy ingestion,
linear growth, weight increase, and gross conversion efficiencies were all
maximal at 27°C-the identical temperature that toads preferred in a thermal
gradient.
After reaching maturity, western toads will return to their natal ponds during
the breeding season. No information is available on the percentage of a
population that disperses to new breeding sites, or the process that catalyzes
colonization. Adult western toads probably experience very little predation and
have high natural survival rates after the larval and juvenile stages (Campbell
1970). Western toads have long adult life expectancies, estimated to survive from
6 years (Stebbins 1985) to 16 years (Blaustein et al. 1998).

IV.

Western Toad Status

The western toad (Bufo boreas) was once widely distributed in the Pacific
Northwest, and occurred throughout the western U.S. In 1985, Stebbins ( 1985)
proclaimed the species to be ubiquitous. Since this time, western toad populations

10

have precipitously declined throughout their former range (Stebbins and Cohen
1995). Although some decline has been accepted as a consequence of
development and human habitat alteration, disappearances of populations from
relatively pristine areas, such as national parks and forests, has raised alann. In
the case of the western toad, alarm has been compounded by the fact that decline
has occurred over a broad geographic range thereby suggesting that global
atmospheric factors are responsible (Lips 1999; Pounds et al. 1999; Blaustein and
Wake 1990).
Stebbins and Cohen ( 1995) provide a comprehensive compilation of
regional western toad decline. In California, Papenfuss (1980), Drost and Fellers
( 1993 ), and Martin ( 1992) all documented decline. Papenfuss surveyed transects
in the Sierra Nevada foothills, finding toads on only five of twenty-seven
transects where the presence of the western toad was classified as highly
probable. Drost and Fellers resurveyed a transect performed by Grinnell and
Storer ( 1924), finding toads at only one of six historical sites, and in extremely
low numbers. In Colorado, Carey (1993) and Com et al. (1989) have also
documented western toad decline. Carey eventually abandoned field studies
begun in 1971 because of severe population declines, and by 1979 eleven
populations had vanished. Corn et al. ( 1989) surveyed fifty-nine historical
localities and found only ten remaining populations (17%). Acid precipitation
and low pH levels have been attributed to these declines, although scientific
research has not proven causality in the declines (Vertucci and Co~ 1993 ).

11

Almost every western state throughout the range of the western toad has
documented a case of decline. In New Mexico, Stuart and Painter (1994)
documented a loss of several populations from the San Juan Mountains. In the
Cascade Mountains of Oregon, Blaustein et al. ( 1994a) documented high levels of
egg mortality, finding 50%, 60% and 95% mortality at three different study sites.
Yet from 1980 to 1989 egg mortality had never exceeded 5%. lN-B radiation
has been attributed to these declines, although other factors such as pathogens
have been implicated as well (Kiesecker and Blaustein 1997). In Utah, western
toads were common up to around the l 960's. Today only a single breeding
population is known to remain. Similar declines have occurred in Wyoming.
Peterson et al. ( 1992) found toads at only three of eight sights in Yellowstone and
Grand Teton National Parks, and at the two sites where toads were found there
were less than ten total individuals. Historically, Carpenter (1953) reported
western toads as the most widespread amphibian in the Jackson Hole region.
Clark et al. (1993) reported similar declines finding toads at only nine of ninetyeight (9%) sites surveyed.
In Washington, the situation is presumably similar to other regions, except
historical information on distribution and abundance is lacking. Lardie ( 1963)
and Slipp (1940) reported Bufo boreas to be abundant and common in Pierce
County and around the Tacoma area. More currently, Leonard et al. ( 1993)
reported the species as uncommon in Western Washington and the North
Cascades for unknown reasons, although development and loss of wetlands have
been implicated. Since the 1700' s, about half of the wetlands in the nation have

12

been lost or severely altered by human activities (Council on Environmental
Quality 1989). In Washington, it is estimated that the greatest losses of
freshwater wetlands and marshes have resulted from development and most of the
wetlands lost were between 0.2 and 2.0 hectares (Canning and Stevens 1989).
Adams and Bury (1998) found six toads at one locality in a survey of the Fort
Lewis military reservation, a relatively undisturbed habitat, where vehicle
maneuvers are prohibited within 50 meters of wetlands. Richter and Azous
( 1995) found western toads at approximately 20% of wetlands surveyed in King
County, although no information on population size was gathered. Other
amphibian surveys (McAllister et al. 1993; McAllister and Leonard 1990, 1991,
1993) suggest decline throughout the lowlands of western Washington. Contrary
to Nussbaum's (1983) assertion that the western toad adapts well to agricultural
and residential suburban areas, this species appears to be in danger of extirpation
from the lowland Puget Sound ecoregion.

V.

Causal Factors in Western Toad Decline
Multiple factors have been implicated in western toad decline, although no

single factor has been proven responsible in all declines (Blaustein and Wake
1990). To better elucidate causal factors in western toad decline in the lowland
Puget Sound ecoregion, each must be investigated, with specific attention given to
the unique regional characteristics.

13

A.

Habitat Loss/Degradation
Habitat loss and degradation has been the most common culprit in western

toad decline (Blaustein et al. 1994), although it cannot explain population
disappearances in pristine areas, such as national parks. Habitat alteration and
development in the lowland Puget Sound ecoregion has been extensive. There are
currently over 4 million people in the Puget Sound ecoregion, with the majority of
growth concentrated along the 1-5 corridor (Puget Sound Health 2002). Between
1990 and 1999 the lowland Puget Sound ecoregion experienced a 19 .9%
population growth rate (Puget Sound Regional Council 2002). Concurrent with
population growth, land conversion is extreme. The greatest wetland losses in
Washington State have been freshwater palustrine marshes and forested wetlands
from 0.2-2.0 hectares in size (Canning and Stevens 1989), which is a size class
that is readily used by breeding amphibians, including western toads. Increasing
evidence suggests that smaller (<4.0 hectares) temporary wetlands often have
higher amphibian species diversity and produce more metamorphosing juveniles
than ephemeral wetlands or permanent ponds (Pechmann et al. 1989; Semlitsch et

al. 1996).
Concordant with aquatic habitat, terrestrial habitats must also be conserved to
maintain amphibian populations. Given the known home range of the boreal toad,
a close relative of the western toad, the approximate size of the terrestrial habitat
utilized is a circle with a 2.3 km radius surrounding the wetland or water body
(Muths 2003). To adequately protect populations of this species a significant
amount of terrestrial habitat must be maintained; a fact which emphasizes the

14

importance of landscape level wetland spatial arrangement and matrix land for
source/sink dispersal. Too often, conservation efforts for amphibians focus on
conservation of aquatic habitats/breeding sites and only protect the terrestrial
habitat around wetlands as "buffer zones" or "buffer strips", thereby denoting a
protective function for aquatic habitats (Semlitsch 2003). In addition, another
problem with contemporary conservation efforts is the fact that the terms used to
define adjacent terrestrial habitat, along with the regulations to protect it, are very
unclear (Semlitsch and Jensen 2001). Moreover, research has confirmed that the
surrounding terrestrial habitat is equally important to many species for performing
essential life history functions. Therefore, it must be stressed that the core habitat
of the western toad has both an aquatic and terrestrial component, and the
conservation of both is required in order to maintain population persistence.

B.

Chemical Contamination
Chemical contamination from acid precipitation and the concurrent low pH

levels have also been investigated as a causal factor in western toad decline
(Vertucci and Corn I 996). Several factors must be considered when making
judgments about the degree or effects of chemical contamination on amphibian
populations. First, only extreme contamination, resulting in mass mortality, is
visible. Secondly, chemical contamination can act on both the aquatic and
terrestrial life stages of amphibians, often having different effects on both. Third,
chemical contamination can have both direct and indirect effects on amphibian
populations.

15

Chemical contamina1·ion o f aquatic
· envtronments

can result in changes in
amphibian distribution, reproduction, egg and larval growth, and mortality (Freda
et al. 1991 ; Freda and Dunson 1985). Aquatic life stage sub-lethal contamination
can result in delayed or early hatching, reduced larval body size, disturbed
swimming behavior, and slower growth rates resulting from diminished prey
capture ability (Home and Dunson 1994; Preest 1993; Bradford et al. 1992;
Andren et al. 1988). Chemical contamination has also been implicated in acting
synergistically with other factors, such as UV-B radiation, to result in decreased
embryo survival (Long et al. 1995). In addition, although no effect may be
observed on amphibian life history variables, chemical contamination may alter
food resources or community composition, which can result in decreased
recruitment into adult populations. Overall, this can be problematic for the
western toad because only 3-5% of all offspring produced annually reach
metamorphosis, and recruitment into terrestrial stages from year to year is
episodic (Semelitsch et al. 1996). Thus, anthropogenic stress from chemical
contamination may further reduce recruitment and/or increase the time interval
between bouts of successful recruitment, thereby affecting the long-term fitness
and demographics of amphibian populations.
Multiple studies have concluded that low pH due to acid deposition is an
unlikely cause of amphibian decline (Vertucci and Com 1996; Dunson et al.
1992). Lethal pHs of the boreal toad (Bufo boreas boreas) range from 3.1 to 4.0
(Porter and Hakanson 1976), and it is likely that the lethal pH of the boreal toad is
representative of the western toad (Bufo boreas). Declines of the boreal toad in

16

the Colorado Rockies could

no

tb

l · d
e exp rune by low pH or acidic deposition

(Com et al. 1989). Carey (1993) speculated that decline in the Colorado Rockies
may have been indirectly caused by chemical contamination, arguing that pH
levels do not need to be lethal to result in population decline and extinction-they
only need to cause stress or increase the susceptibility to infection. Although
largely terrestrial, boreal toads must rehydrate daily require contact with water
during hibernation, which would likely result in stress if chemical contamination
is present (Campbell 1970). Supporting Carey's (1993) assertions for a synergism
between causal factors resulting in stress, which eventually leads to decline, Long
et al. ( 1995) found low pH and UV-B radiation acting in concert to reduce
embryonic survival. Clearly, the direct, indirect, and synergistic effects of
chemical contamination must be considered whenever addressing amphibian
decline.
In the case of the western toad in the lowland Puget Sound ecoregion, little
research has been directed toward water quality with regard to amphibian decline.
In a study of King County amphibian richness and wetland characteristics, Richter
and Azous ( 1995) concluded that water quality was not an acute problem that
could account for decreased amphibian richness. They reported all water quality
characteristics at concentrations below documented levels for deformities and
mortality (Power et al. 1989). However, they did note the lack of information on
sub-lethal impacts and synergistic effects that could contribute to decreased
amphibian richness. Although chemical contamination should be investigated as
a causal factor in western toad decline, little direct evidence supports this factor,

17

especially when considerin th
.
g e amount of precipitation the region receives and
th e broad geographic range of decline.

C.

Climate Change and UV-B Radiation
Climate change and other atmospheric factors such as increased UV-B

radiation, have also been implicated and investigated in amphibian declines
(Pounds 2001; Blaustein et al. 2001; Blaustein et al. 1994a). It is unclear how
global climate change will affect amphibian populations, although it is logically
assumed that effects will be site specific, as well as species specific. Several
attempts have been made to ascertain global warming impacts on amphibian
populations by examining breeding phenology.

Several studies have shown

amphibian populations are breeding earlier (Gibbs and Breisch 200 I ; Beebee
1995); whereas others have suggested that early breeding may be related to mean
daily temperatures over the 40 days previous to breeding activity (Reading 1998).
Although difficult to prove conclusively, global warming will impact amphibian
populations if weather patterns, temperature, and precipitation are altered. Aside
from altering the ambient environmental conditions of home ranges, including
temperature, humidity, moisture, rainfall, and changes in hydroperiods of aquatic
sites-indirect effects such as increased stress could also result in increased
susceptibility to parasites and disease (Donnely and Crump 1998).
Climate change has been investigated as a causal factor in western toad
decline (Blaustein et al. 2001 ; Pounds 2001 ). Blaustein et al. (2001) did not find
significant changes in breeding phenology in four populations of the western toad

18

in the Oregon Cascade R
population did exhib1·t

.th .
ange WI mcreasing temperatures, although one

· •fi
a nonstgru 1cant trend towards earlier breeding. Pounds

(2001) suggested anoth

d I c. h
.
er mo e 1 or t e role of climate change in western toad

decline. Beginning with the El Nino/ Southern Oscillation in the tropical Pacific,
wanning trends since the l 970's have reduced winter precipitation in the
Cascades, which has resulted in reduced winter snow pack and concurrently
reduced spring water levels in lakes and ponds. Thus, western toads have been
depositing their eggs at reduced water depths. This leads to increased exposure to

UV-B radiation, which can result in the increased vulnerability of western toad
eggs to infection from Sapro/egnia ferax (Blaustein et al. 1994b). Indeed, in
water less than 20cm deep, Saprolegnia ferax invades and kills about 80% of
embryos; in sharp contrast when compared to 12% in water deeper than 50cm
(Kiesecker et al. 2001a). Clearly, climate change must be addressed when
considering amphibian decline, and unfortunately, remedial actions are limited in
the short term.
UV-B radiation has also been investigated as a causal factor in amphibian

decline. Blaustein et al. ( 1994a) experimentally showed that western toad embryo
hatching success was significantly greater when eggs were shielded from UV-B
radiation. They also found that western toad photolyase levels, an enzyme that
repairs UV-B damage, was one-sixth the level present in Pacific treefrog (Hy/a

regilla), a species that seems unaffected by UV-B radiation. This study generated
considerable controversy, and stimulated numerous studies and articles in refute.
Corn ( 1998) found no relationship between embryo mortality and UV-B radiation

19

in the southern Rocky M
1996) and Licht and G

t •
hi .
oun am amp b1an populations. To date, Licht (1995;

ran

t ( 1997) h

ave been the most vocal opponent of the UV-

8 radiation hypothesis Ab·1 t · 1
.c.
·
0 IC actors such as water depth, water color, and
.c.

dissolved organic matter, along WI"th b"10t·1c 1actors,
such as Jelly
capsules around

eggs, melanin pigmentation of eggs, and the color of larvae and metamorphosed
forms, are all proposed as factors that negate the potential negative impacts of
UV-B radiation on amphibians. Palen et al. (2002) assessed 136 aquatic breeding
sites across the Pacific Northwest, finding that 85% of sites were naturally
protected from UV-8 radiation by dissolved organic matter, thus only a small
fraction of the clearest waters experience UV-8 levels exceeding levels associated

with elevated egg mortality.
Although these criticisms of the UV-B hypothesis are applicable, multiple
studies have shown that UV-B radiation can act in tandem with other factors to
produce mortality. UV-B has been shown to act synergistically with pathogens,
low pH, and climate change to increase embryo mortality. Kiesecker and
Blaustein ( 1995) showed UV-B radiation and a pathogen (Saprolegnia ferax) act
synergistically to kill amphibian embryos, with the combined effects of both
factors being greater than either factor acting alone. Long et al. ( 1995) found a
similar synergistic relationship between UV-B radiation and low pH. Although
neither factor acting alone had a detectable effect on embryo survival, in concert
they led to a significant decrease in embryo survival. Additionally, Kiesecker et
al. (2001a) found a synergistic reaction between climate induced water level

20

reductions, UV-B radiation and •
d
mcrease vulnerability to pathogen infection of
,
embryos.
. Although UV -8 radiation may not be the ultimate cause of mortality for
amphibian embryos, it has been suggested that UV-8 radiation and other factors,
such as habitat degradation and chemical contamination may stress organisms and
increase their vulnerability to infection (Schaefer et al. 198 l ). Furthermore, life
history attributes of the western toad may contribute to increased probability of
infection by pathogens when stressed. Species that Jay eggs in communal egg
masses, such as the western toad, have been shown to experience higher egg
mortality rates from Saprolegnia ferax infection (Kiesecker and Blaustein I 997).
The authors suggest that UV -8 radiation and other stress causing environmental
conditions, such as low pH and low temperature, may weaken amphibian immune
systems, and therefore increase their vulnerability to infection. Thus, UV-B
radiation must be carefully examined as a contributor to amphibian declines
because of its ability to act directly and indirectly through multiple pathways. In
the case of the western toad in the lowland Puget Sound ecoregion, UV-B
radiation is probably not a direct cause of embryo mortality because the harmful
effects of UV -B radiation are diminished at lower elevations; however, indirect
effects, such as increased stress, are possible.

21

D.

Invasive/ Introduced Species
Invasive species have also been implicated in amphibian decline (Fisher and

Schaffer 1996). Fish stocking and the introduction of bullfrogs (Rana

catesbeiana) have had the most deleterious effect on native amphibians in the
Pacific Northwest. Additionally, in the lowland Puget Sound ecoregion, habitat
modification often benefits introduced bullfrogs and introduced fish by converting
large ephemeral wetlands to permanent small ponds with less shallow water and
emergent vegetation (Richter and Azous 1995). Fisher and Shaffer (1996), in
their survey of California's Great Central Valley, found that native amphibians
and introduced fish and bullfrogs tended not to co-occur; introduced exotics
tended to occupy the low elevation sites and native species tended to persist at the
higher elevations. Although plausible, western toads are less susceptible to
adverse effects from introduced fish for two reasons: I) western toads often breed
in ephemeral water bodies that do not harbor fish; and 2) western toad larvae
contain bufotoxins, so fish tend to avoid eating them (Peterson and Blaustein
1991 ).
Although western toad larvae may not be susceptible to predation by
introduced fish, fish stocking may indirectly introduce pathogens such as

Saprolegnia ferax (Kiesecker et al. 2001 b). It has been estimated that 45% of the
mountain lakes in the western U .S have been stocked with fish (Bahls 1992).
Continued stocking of introduced species in mountain lakes for sport fishing will
continue to adversely affect native amphibians. Even after fish stocking has been
discontinued, introduced pathogens may become established and further stocking

22

may introduce new strains of pathogens as they emerge. Furthermore, Blaustein
et al. (1994b) hypothesize that infected amphibians may transmit the pathogen to
other populations as they migrate or disperse.

Therefore, invasive/introduced

species have undoubtedly had adverse impacts, both directly by predation and
indirectly by pathogen introduction, on populations of the western toad in the
lowland Puget Sound ecoregion.

E.

Pathogens
As mentioned previously, pathogens may also play a role in the decline of the

west~m toad. To date, two pathogens have been identified that have been
experimentally shown to increase embryo mortality or produce malformations.
Blaustein et al. (1994) identified a species of water mold (Saprolegniaferax) that
had infected western toad egg masses and resulted in 95% mortality. S.ferax is
an important worldwide pathogen of fish, and may have been introduced to
amphibian populations by fish stocking. Blaustein et al. (1994) speculate that
several years of extreme egg mortality may be attributable to this fungus. Followup research has shown that fish infected with S. ferax are capable of transmitting
the pathogen to both amphibians and sediment, thereby establishing pathogen
populations (Kiesecker et al. 2001 b).
The trematode parasite (Ribeiroia ondatrae) has also been shown to induce
severe limb malformations and reduce survivorship in western toads (Johnson et
al. 2001 ). This parasite exhibits a complex life cycle involving a primary host and
two intermediate hosts. Generally, the primary host will be avian, followed by a

23

secondary snail host, and then lastly a secondary amphibian host. Upon reaching
the amphibian host, the parasite forms cysts on the tadpoles' skin, which penetrate
the tissue. These cysts disrupt natural limb bud formation, and result in
malformed adult amphibians. Ribeiroia will parasitise any stage in amphibian
development, although only attack at larval stages before limb budding will
induce substantial abnormalities (Sessions et al. 200\).
Speculation abounds as to why amphibian populations are seemingly more
vulnerable to infection and parasitism in the more recent past. Green et al. (2001)
examined museum preserved specimens of Yosemite toads (Rufo canorus) from a
die-off in the 1970' s in an effort to elucidate a causal factor. Inability to find a
primary etiological agent, but finding a variety of infectious diseases, Green et
al.' s (2001) work suggests that the toads' immune systems were suppressed.
Immune system suppression has been attributed to physical and environmental
stressors, including handling, toe clipping, predation, unusual temperatures or
weather patterns, UV-B radiation, and habitat alteration/ degradation (Kiesecker
et al. 2001 a; Carey 1993 ). Ultimately, western toad decline seems to be the result
of a multifaceted attack on every life stage and at every type of environment that
the toad encounters, with each attack compounding the probability of mortality.

VI.

RESULTS
Field surveys confirmed nine sites of presence, fourteen sites of absence, and

two sites that were indeterminate (Table 1). Figure 7 represents all sites visited
and included in this investigation. Figures 8-22 show each site, including the

24

buffer, land use and pie graph of land use within each buffer. Of all 25 sites, 12
sites were located on Fort Lewis Military Reservation, due primarily to the
considerable resources allocated to monitoring on base. Site #6, Nisqually Lake,
was not monitored because it is located in the Artillery Impact Area of Fort
Lewis, and therefore resulted in a designation of "unable to determine presence or
absence". Additionally, site #22, Bear and Porter Creek in Snohomish County,
although surveyed twice, presence or absence of western toads was difficult to
establish due to the number of possible breeding locations within the beaver dam
complexes of the two creeks and the dense vegetation restricting movement and
sight; consequently this resulted in a categorization of "unable to determine". The
remainder of sites were thoroughly surveyed with a high degree of confidence in
the designation of presence or absence.
Land use within a 2.3 km buffer of each site was determined using GIS
analysis of land cover (Table 2). Considering all sites, the maximum percent
developed was 18.9% (site# 13, Fagan and McEnniery Lake), while the least
developed site was 0% (site# 6, Nisqually Lake). A comparison ofland use at all
sites, categorized as agricultural, residential and industrial, is shown in Figure I .
A comparison of total development at all sites is shown in Figure 2. Land use at
sites of presence is shown in Figure 3. Land use at sites of absence is shown in
Figure 4. Figure 5 represents a modified data set, showing percentage of each
land use at included sites. Figure 6 represents a modified data set, combining
industrial and residential development at included sites.

25

VII.

DISCUSSION
The results of this investigation confirm western toad decline in the

lowland Puget Sound e

·
d•
.
.
coreg1on an mconclus1vely implicate habitat loss as a

·
causal factor. Of the twenty-fltve st·1es o f h.1stoncally
confirmed sightings since
1985, current presence was confitrmed or was unable to determme
· at eleven sites
·

(44%), while the remainder of sites did not support western toad populations
(56%). Current decline revealed in this study should be considered concurrently
with far more severe historical decline not covered in this paper. In addition,
although decline was confirmed by field surveys, several caveats must be
addressed in unison with the results.

A.

Field Surveys
First, surveying of sites only assessed presence, absence, or inability to

confirm. Therefore, presence could merely be the sighting of a single toad. This
was the case at two sites of presence (Agnew Lake, site #18; Cat Lake, site #1).
Therefore, these sites may not constitute source breeding populations, only
dispersal sink sites from more robust breeding populations elsewhere on Fort
Lewis. Even though a single toad doesn't constitute a breeding population, the

life history of the western toad implies that these solitary toads were present to
engage in breeding, because toads only aggregate at water bodies during the
breeding season. Moreover, surveying only provided a glimpse of the breeding
period, and once presence was confirmed monitoring progressed to other sites.
Other toads may have arrived before or after monitoring, which would have
allowed for reproduction.

26

Confirmation of absence is also plagued with difficulty, particularly when
considering the fact that absence cannot be proven. Surveying generally consisted
of a single, thorough assessment in a brief period of time. However, the
possibility of missing a breeding aggregation was minimized by surveying sites
according to elevation corresponding with the onset of breeding at the lowest
elevation sites. Additionally, it is possible that some sites experience episodic
breeding every few years, which is made possible by the longevity of the species,
yet this would also suggest an unstable population that is highly vulnerable to
stochastic events.
The results of field surveying in conjunction with the historical sightings
database suggest the western toads on Fort Lewis exhibit a metapopulation
structure, with source populations providing dispersal to sink sites. At Fort
Lewis, Fiander Lake (site #17), Jolly Lake (site #12), and Cat Lake (site #1)
appeared to be the sites of source populations, where breeding aggregations were
found or heard. The remaining seven sites on Fort Lewis are all located within
the home range buffer of source populations, suggesting that they act as episodic
breeding sites in years following successful recruitment and dispersal from source
populations (Figure 8). During the surveying season, No Name Lake (site #11),
Rainier Training Area (site #10), and Bog Pond (site #15), historical breeding
locations, received inadequate winter and spring precipitation. Consequently, this
resulted in all of the aforementioned sites failing to fill with water, thereby
negating any chance of successful reproduction. Given the metapopulation
structure, maintaining the integrity of stable, reliable source sites (Fiander, Jolly,

27

and Cat Lake) and the surrounding terrestrial home ranges should be a priority in
the conservation of the western toad on Fort Lewis.
Two additional sites, Ranger Lake (site #14) and Fagan & McEnniery
Lake (site #13), are also possible dispersal sites from Fort Lewis (Figure 13&14).
Both sites currently do not support western toad populations, yet presence has
been confirmed by historical sightings. Although both sites are outside of the
known home range buffer, they are located in close enough proximity to Fort
Lewis that it is feasible for dispersal to have established these sites as historical
breeding populations. Dispersal to these sites is possible because the terrestrial
environment between Fort Lewis' source populations and each site is relatively
undisturbed; although land conversion is accelerating, reducing the likelihood of
future dispersal and the rescue effect-where dispersing individuals supplement an
existing population with genetic diversity and increased reproductive potential-an
important process for population persistence and fitness (Blaustein et al. 1994c).
Another monitored site that also followed a similar source/sink dispersal
pattern was Wye Lake (site #8) which appears to be a source population (Figure
12), with dispersal to Koenaman Lake ( site #5). Koenaman Lake is
approximately 2.3 km from Wye Lake, and therefore coincides with the literature
supported home range area (Muths 2003; Bartlett 2000). Field surveying and
home range examination also supports the metapopulation dynamic of the western
toad populations. This fact justifies the modification of sites considered in land
· m
· an attempt to elucidate the responsibility of habitat loss in western
use anal ys1s
toad decline.

28

An additional site surveyed and included in land use analysis of this study
was of questionable validity. Tarboo Creek (site #2) was identified as a site of
potential breeding because of a tadpole sighting (Figure 9). yet, it must be noted,
that the tadpole life stage is the most difficult life stage at which to identify
western toads because of the similarities that western toad tadpoles have with
numerous other species. Also, this site was the only creek visited during
surveying. Western toads generally prefer small, reliable, standing water bodies
for breeding. For these reasons, it is probable that misidentification of tadpoles
occurred; consequently, Tarboo Creek was removed from GIS analysis of land
cover in the modified data sets (Figures 5 & 6).
An additional site that requires further consideration is site #20, Carson
Lake (Figure 19). Land use analysis suggests this site is suitable to support a
population of western toads, although surveying resulted in a designation of
absence. Upon further examination of the surrounding terrestrial habitat, it is
probable that this sighting was a dispersing juvenile from an unidentified breeding
site in close proximity. Several potential breeding sites are within 3km of Carson
Lake, and further monitoring should reveal an undiscovered source population.
Although included in analysis as a site of absence, the identification of a breeding
population in close proximity, signifying a metapopulation sink site, would justify
the removal of Carson Lake from analysis.

B.

GIS Analysis
Analysis of land use in this study did not include habitat alteration caused

by Jogging. Logging is a common habitat alteration that has occurred at all of the

29

sites visited. The inherent difficulty with assessing the impact of logging on
western toad population derives from the variability in both temporal and spatial
parameters, imprecise or lacking information on the location and date of logging
operations, and time lags in the publication of land conversion. Logging
invariably impacts western toad populations due to changes in microclimate,
moisture, vegetation, insect community composition, soil composition and
structure, predation pressure, and temperature. To adequately assess the impact of
logging on the western toad, research would need to identify and monitor an
undisturbed population, subject it to a logging operation, and then fol1ow this
population with intensive monitoring and, ideally, telemetry data. This type of
experiment exceeded the scope of this project, although it would be greatly
beneficial to future management efforts. Obviously, logging operations do impact
and affect the western toad populations considered in this study, although,
because of the difficulties inherent in assessing logging impacts, they were not
evaluated in this analysis, but should be considered qualitatively with the results.
The land use at sites of presence and absence is shown in Table 2 and
Figures I, 3 and 4. Total development at each site is shown in Figure 2.
Although there are some anomalous results, the general trend expresses a negative
relationship between development and western toad presence. The average
development at sites of presence was 3.17%, while average development at sites
of absence was 5 .06%. By modifying the data, excluding sites of metapopulation
.
al ( s1·te #5 , Koenaman Lake·, site #10 , Rainier training area; site #11, No
d1spers
Name Lake; site #15, Bog Pond; site #19, Pothole Ponds; site #21, States Marsh;

30

site #24 , Toad Ponds) , and s1·1e #2 , T arboo Creek (because of possible
·
misidentification), a more obvious trend emerges (Figure 5). Except for two sites
of absence (site #20, Carson Lake; site #14, Ranger Lake) and a single site of
presence ( site # 18, Agnew Lake), a clear trend becomes apparent; less
development equates to an increased likelihood of western toad populations.
Although included in the modified data set, it may also be appropriate to include
Agnew Lake ( site # 18) as a sink site from other source populations on Fort Lewis.
Thus, when Agnew Lake is excluded, the results of this study are further clarified.
A further modification involves reducing land use considered in analysis to
include only residential and industrial development (Figure 6). Excluding
agricultural development may be appropriate depending on the intensity with
which the land is worked and the type of agricultural good produced. Western
toads may be able to forage and move through a variety of agricultural
landscapes, including orchards and non-industrial, low intensity crops. Sites of
absence in this scenario average 4.42% habitat loss within the 2.3 km buffer,
while sites of presence average 1.18%. Figure 6 suggests that western toads have
a threshold of acceptable habitat loss to industrial and residential development
within their terrestrial home range. This threshold is around 4%.
The significance of buffer size used in analysis should also be given
consideration. Although the literature suggests a home range buffer of 2.3 km,
representing the maximum distance a toad will move away from breeding sites
during the season, several variables must concurrently be addressed. Female
western toads are known to move greater distances, averaging 2.4X the distance

31

of males (Muths 2003). Significantly smaller buffers would be adequate to
protect male populations, although female western toads generally compose a
small fraction of the population, around 25% (Campbell 1970). Therefore, the
female populations and home ranges should be the focus of conservation efforts.
Additionally, 2.3 km represents the farthest movement away from breeding sites,
not the average. Using a smaller buffer in analysis may have been more useful,
possibly using the average distance traveled, instead of the maximum. Upon
examination of the site maps, a smaller buffer would have likely provided a more
obvious trend, suggesting a stronger association between habitat loss and absence.
Qualitatively, the majority of sites of absence had intensive development in close
proximity to breeding sites, while sites of presence generally had less
development in close proximity. Concurrently, sites of presence generally had an
undeveloped avenue to terrestrial habitats immediately adjacent to breeding sites.
Information on dispersal trajectory from breeding sites should be a priority in
western toad conservation, because relatively little is known about their
movements or activities away from breeding sites, or the rates of exchange
between populations (Alford and Richards 1999).
The importance of the terrestrial habitat should be a priority in
conservation efforts, especially in the case of the western toad, a largely terrestrial
amphibian. To ensure population persistence and fitness, a significant amount of
terrestrial habitat surrounding the breeding site should be maintained intact.
Semlitsch (2003) provides a useful model that could be integrated into western
toad conservation efforts. The model provides: 1) a protected aquatic habitat

32

surrounding the breeding st·te,· 2) a core ha b"1tat core habitat
· encompassmg
· the
aquatic buffer surrounding the breeding site; and 3) a secondary terrestrial habitat
buffer surrounding the core habitat that is subject to limited nonpennanent
extractive uses. This model would provide adequate protection to species such as
the western toad that utilize a significant amount of terrestrial habitat during the
majority of their life cycle. If possible, habitat corridors between source and sink
sites should also be maintained, thereby ensuring the fitness, stability, and
persistence of populations. Multiple examples are provided by the results of this
investigation, including Fort Lewis and Wye Lake/Koenaman Lake.
The importance of the terrestrial habitat to western toads cannot be
understated. Multiple studies have pointed to the importance of focusing
conservation efforts on post-metamorphic vital rates, thus requiring the protection
of adequate terrestrial habitat (Biek et al. 2002; Vonesh and De La Cruz 2002).
Vonesh and De La Cruz (2002) found that even extreme egg mortality, which was
attributed to increased UV-B radiation, was insufficient to result in the declines
observed in western toad populations. This suggests that western toad abundance
is more sensitive to changes in survival of later stages than the egg stage. In
addition, Biek et al. (2002) found post-metamorphic vital rates are far more
important to amphibian population persistence and fitness, thus making the
prevention of perturbations in the later life stage vital rates a priority in the
management and conservation of the western toad. To successfully accomplish
this task, terrestrial habitat requirements must be determined and concordant
habitat surrounding breeding sites must be maintained.

33

Several sites of western toad presence investigated in this study are
nearing the threshold of development compatible with this species. Site # 25,
Echo Lake (Figure 22), had a seemingly robust population of western toads,
although the amount of development adjacent to the site was confounding (Figure
22). Interstate 90 runs within 200 yards of the lake, effectively reducing the
terrestrial home range by half. All dispersal and home range movements must be
directed away from the interstate. Homes also dot the lakeshore. If development
continues around this lake it is likely that the western toad population will not
persist. The only hope for this population is that the terrestrial habitat to the south
east of the lake remains intact.
Another site in a similar situation is site #8, Wye Lake. Wye Lake is
experiencing significant residential development (Figure 12). Houses surround
the lakeshore of this breeding site. The only avenue for dispersal into the
surrounding undeveloped terrestrial habitat is plotted out for sale and
development. Given continued development around the lake, essentially
insulating it from breeding toads, this population will likely be lost. Site #7,
Anderson Lake had the most development of any site of western toad presence
(Figure 14), excluding site # 18, Agnew Lake, which is a probable dispersal site on
Fort Lewis (Figure 8). This site most likely maintains a population of breeding
western toads because it is buffered by Anderson Lake State Park. All
development has occurred outside of the park boundaries, possibly making it a
useful research site to determine minimum home range requirements. Given the
date of the land use data set used in this study-1999-coupled with the accelerating

34

rate of development in the Puget Sound , it
· 1s
· essential
· that western toad breedmg
·
· before populations
·
sites are monitored and evaluated .c.1or poss1"ble protection
are
lost. This is especially relevant when considering the fact that western toads do
not effectively exploit new breeding sites or artificial ponds (Monello and Wright
1999).
Aside from development, a new threat has emerged that may accelerate
western toad decline in the lowland Puget Sound ecoregion. The effects of
climate change on breeding phenology became readily apparent during the
monitoring conducted for this study. As previously mentioned, several historical
breeding sites on Fort Lewis failed to fill with water. Additionally, breeding
began several weeks earlier than in the past. Concurrent with straightforward
consequences of climate change, including ponds failing to fill and breeding
timing being altered, Kiesecker et al. (2004) have suggested another associated
pathway for decline. Foilowing decreased rainfall, which results in lower water
levels in breeding ponds, increased levels ofUV-B radiation penetrates western
toad eggs, increasing the likelihood of Saprolegnia ferax infection, which results
in greater than 50% egg mortality. Although the lowland Puget Sound ecoregion
receives less UV-B radiation than higher elevations, the stage is set for disaster.
To ensure population persistence of the western toad in the lowland Puget Sound
ecoregion, actions must be taken immediately to conserve an invaluable
component of our natural heritage.

35

VIII. CONCLUSION
Several conclusions emerge fro

m

th

. .

.

.



e resu1ts of this mvest1gatton. Frrst, the

westem toad is in decline throughout the region, nearing 60% since 1985, in
·
· ev1"dence 1mp
· 1·1cates
addition to severe histon·cal declm·e • Secondi y, mcreasmg
habitat loss as the causal factor behind declines. Figure 2 exemplifies this trend
most effectively. Modifications to the data set (Figures 5 and 6) further link
habitat loss as a causal factor in western toad decline. Because the western toad is
a "species of concern" in Washington State, it is imperative that actions be taken
immediately to halt decline and ensure current population persistence, expansion,
and, possibly, reintroduction. Steps include the protection of current breeding
population terrestrial core habitats; continuing research and monitoring of existing
populations in order to improve knowledge of terrestrial habitat movements and
requirements; and the development of a conservation/reintroduction plan to be
implemented to ensure population persistence, stability, and fitness. Given the
small number of current breeding sites in the lowland Puget Sound ecoregion,
protection of current populations could be ensured at a minimal cost. By
restricting further development around current breeding sites, as well as the
management and protection of terrestrial habitats in order to reduce impacts,
population persistence will be probable if climate change, UV-B radiation,
chemical contamination, invasive species, and pathogens do not contribute to
further declines.
The western toad is a unique and exquisite species that plays an integral role
in western Washington ecosystems, and remains a valuable element of the area's

36

natural heritage. Prudence demands action and commitment to the preservation of
a complete flora and fauna assemblage in the lowland Puget Sound ecoregion.
The time to act is now, before further decline occurs, while populations are still
viable, unless we are willing to relinquish the western toad to follow in the
footsteps of the now extinct Costa Rican Golden Toad (Bufo periglenes), and the
Australian gastric brooding frogs (Rheobatrachis silus and R. vitellinus). In the
words of David Quammen in The Song of the Dodo ( 1996), "Meanwhile, though,
there's still time. If time is hope, there's still hope."

37

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47

Table 1

Field Survey Results

Site
Elevation
Number
(Feet)
I
---

Date
County
Site Name
Visited
3/31/04
T hurston
Cat Lake
4/2/04
;omments: Single juvenile toad; heard breeding aggregation.
16
3/28/04
Jefferson
Lower

Presence/
Absence
Presence

Absence
Tarboo
Creek
Comments:
Only creek visited; possible mis-identification of tadpoles.
-,
.)
l 00
4/2/04
Thurston
Lake St.
Absence
4/3/04
Clair
Comments: Canoed N. end of St. C lair and visited small lake across road.
4
200
3/28/04
Jefferson
Crocker
Presence
Lake
Comments: Caught 2 adults on N . end of lake and 1 adult and 3 toadlets on S.
end.
5
209
3/30/04
Kitsap
Koenaman
Absence
Lake
Comments: No toads or eggs; possible dispersal site from Wye Lake.
6
230
-------Pierce
Nisqually
Unable to
Lake
Determine
Comments: Unable to visit because of location in Artillery Impact Area of Ft.
Lewis.
7
262
3/28/04
Jefferson
Anderson
Presence
Lake
Comments: Over 50 toadlets observed and photographed.
8
293
3/30/04
Kitsap
Wye Lake
Presence
4/5/04
Comments: 20 toad breeding aggregation; vocalizing.
9
318
3/29/04
Mason
Oak Patch
Presence
Lake
Comments: Numerous adults and juveniles; several in amplexus; egg strings
present.
10
383
3/31/03
Thurston
Rainier
Absence
Training
Area
Comments: Possible sink site from source populations on Ft. Lewis.
II
3/3 1/04
391
Thurston
No Name
Absence
Lake
Comments: No water this year; possible sink site from source populations on Ft.
Lewis.
3/31/04
12
394
Thurston
Jolly Lake
Presence
4/ 1/04
Comments: Saw fi ve single males; 2 amplexed pairs; egg strings; dead juvenile.
48

Site
Number
13

Elevation
(Feet)
399

Date
Visited
4/3/04

County
Thurston

Site Name

Presence/
Absence
Absence

Fagan and
McEnniery
Lake
Comments: No toads or eggs· highly developed ·th ·d
d
d
WI
res1 ences an roa s.
'
14
406
3/31/04
Thurston
Ranger
Absence
4/2/04
Lake
Comments: Waded lake; similar habitat to other source populations of Ft. Lewis.
15
421
3/31/04
Thurston
Bog Ponds
Absence
Comments: Possible sink site from source populations on Ft. Lewis.
16
441
4/6/04
King
Beaver Lake Absence
Comments: Highly developed; spoke with resident who last saw toads 15 years
ago.
17
445
3/31/04
Thurston
Fiander
Presence
Lake
Comments: Over 50 toads; vocalizing; amplexus; egg strings.
18
446
3/31/04
Thurston
Agnew
Presence
4/1/04
Lake
Comments: Saw single juvenile; ~ood habitat; possible sink site from source site.
19
448
3/31/04
Thurston
Pothole
Absence
Ponds
Comments: Possible sink site from source populations on Ft. Lewis.
20
461
3/29/04
Mason
Carson Lake Absence
Comments: No toads, eggs or metamorphs; high degree of logging around site.
21
477
3/31/04
Thurston
States
Absence
Marsh
Comments: Possible si.nk site from source populations on Ft. Lewis.
22
508
4/4/04
Snohomish
Bear and
Unable to
4/6/04
Porter
Determine
Creeks
Comments: Beaver dam complex; vegetation too dense and too many ponds to
determine.
23
Whatcom
Our Lake
4/4/04
531
Absence
Comments: Highly developed and polluted; trailer park surrounds lake; dead rat.
24
558
3/31 /04 I Thurston
Toad Ponds Absence
Comments: Possible sink site from source populations on Ft. Lewis.
25
908
4/6/04
I King
.
Echo ~ake
Presence
c omments: _,. , amp lexed pairs·, l O males·, floatmg far out m lake compared to
other sites.

49

Table 2
Site#
ocation)
1-Cat Lake
2-Tarboo Creek
3-Lake St. Clair
4-Crocker Lake
5-Koenaman
Lake
6-Nisqually Lake
7-Anderson Lake
8-Wye Lake
9-Oak Patch Lake
IO-Rainier
Training Area
11-No Name
Lake
12-Jolly Lake
13-Fagan and
McEnniery Lake
14-Ranger Lake
15-Bog Pond
16-Beaver Lake
17-Fiander Lake
18-Agnew Lake
19-Pothole Ponds
20-Carson Lake
21-States Marsh
22-Bear and
Porter Creek
23-Our Lake
24-Toad Ponds
25-Echo Lake

Land Use Analysis Pe

rcentages

%
Industrial
0.2%
0%
1.2%
1.1%
0.2%

Residential
0%
0%
2.8%
0.05%
0.4%

%
A2riculture
2.4%
0.2%
8.2%
0.05%
0%

%
Developed
2.6%
0.2%
12.2%
1.2%
0.6%

0%
0.7%
0.4%
0.1%
0.1%

0%
3.0%
2.0%
0%
0%

0%
4.5%
0%
0%
0.5%

0%
8.2%
2.4%
0.1%
0.6%

0.1%

0%

2.0%

2.1%

0.2%
1.5%

0%
2.4%

3.8%
15.0%

4.0%
18.9%

0.2%
0.1%
1.1%
0.1%
0.8%
0.2%
0.5%
0.2%
0.02%

0.5%
0%
5.5%
0%
1.7%
0%
1.3%
0%
0%

0.2%
0.8%
2.6%
0.2%
11.2%
8.9%
0%
4.0%
0.06%

0.9%
0.9%
9.2%
0.3%
13.7%
9.1%
1.8%
4.2%
0.08%

1.1%
0.1%
1.4%

8.4%
0%
0.8%

0.6%
0%
0.1%

10.1%
0.1%
2.3%

%

50

Figure 1
Site Land Use Comparison
20.00%

18.00%

□ Agriculture


Residential
□ Industrial

16.00%

"t,

12.00%

,_

,-

10.00•4

,_

,-

Q)

Cl.
0

Q)

>

Q)

0
~

8.00%

-- --

6.00%

,_

-

,_

r-

-

,_

4.00%

r-

,-

,_

r-

I-

I-

2.00•4

-

-

,_ ,_

-

- -

,_

,..

-

-

-

,_ r- -

nnEl D □ ~
Q

0.00%

o

Sites (* Denotes Presence/ Unable t o Determine)

51

Figure 2

A ll Sites Dev elopment Comparison
20
18

Absence
Presence

16




14
"C
C1>
Q.

->

r,

12

0

C1>

0

r---

r

,-

10

C1)

~
0

r

,-

8
r-

,-

r

r--

r--

r---

r

r

r

~

r

r

r

'

r---

r

r

r--

r---

r

r -

r--

r

,-

~

r---

6
4

2

.- .-

- .=

-= n

u n D __Q_I]
'q'

52

l

l

~

l

r---

I

ro M
N..-t--O,<D~~..-..o . . - 1 0 r o ~ ....
N:it:..-..:it::it:
:it :it

I

Figure 3
Presence: Land Use Comparison
1s.00%
14.00%

r ----------- - - - ---__,

lr=,---------_f"--------.

r------------1 □□ Agriculture
r-----------l Residential

"C 12.00%
Cl)

0.. 10.00%
0

-

~

□ Industrial

8.00%

Cl)

C

6.00%

~

4.00%
2.00%

00

"c.o

:it

~

Site (*denotes Unable to Determine)

Figure 4
Absence: Land Use Comparison

20.00%
r-

18.00%

"C
Cl)

□ Agriculture

16.00%
14.00%

□ Residential

0

12.00%



Cl)

10.00%

a.

>
Cl)
C
....._o
0........

-

6.00%

t-

r--

t- ,__.

r-

1--

,__.

r-

r-

r-

,-

-

,......

r-

-

4.00°/c0

0.00°/c0

-

- -- -

8.00%

2.00'1/c0

Industrial

r--

,.....
r-

.._

-

,__.

II
,....

,....

IJ
0

Site

53

n
....v ....

El

U')

,-,
U')

:it:

,-,

....
0

N

:it:

v

N

:it:

Figure 5
Land Use (Modified)

20
"C

(1)

C.

->

15

□ Agriculture

0

(1)

10

(1)

C



Residential



Industrial

5

~
0

0
M

-ic

00

~

MM<D-IC

~

-ic

-ic

-IC

-ic

0-IC

~-ic

-IC

-ic

Site # (* Denotes Presence/Unable to Determine)

Figure 6
Industrial and Residential Development
(Modified)
10
"C
Cl)

C.
0
Cl)

>
Cl)
C
~
0

9
8
7
6
5
4
3
2

1

..
-....

..

....
.... ....
....
....
....

-

... - ....
... .... -"' .... "' ... .... .... .... ....



Absence



Presence

-

.__
,___
.__

'

,,.

,-

li1

l llill -

~

~N'-'t--a>N<D

OM<DMM~~w~~~-N'-'

-IC

N~~N~00~N~~~~N<D
~
N
~
N

'-'

'-'

Site#

54

'-'

N

Figure 7 Survey Sites
,.J

Area of
Investigation

' ~•
•1,l,

0

·}

'

/f.~
"-; -:':' 1l' ..~-



....._
0

.... '

0

0

0

0

..;

·-

.

·~-

·. .,_,-~

.......

:

;.
f>

..

_

•J



E>

'-

~
e

? ...

::,. ~'"

0

Presence

Q

Absence



Unable To Determine

~ Kilometers
O 4 8

55

16

·24 . 32

Figure 8

r

,,,...'.1-Fo~

J. ·



o~t

......

wis

...

.

1 10%
11.20%
□ ln dustr1.,1
D Rcsklcnll:il
D Agriculture

30%



Undeveloped

0

..

0

0

·'

0
0

Site #17: Flcrndcr Lako and us~

0

..

a lndutttLil
O Agricutturo
o Undevelo

0

d

Site U24: Toad Pon ds Land l..lse

0 .-idustrL,1
O Agrlc utture
a Undevc k>

d

Site # 10 : Rain ier Trnining Arc.a l:

0~ 1 0%,,

0 .50%
o lndu.iG-1:il
a Agr1cutl:ure

99.40•/o

I

- Io Undeveloped

56

I

ii

Figure 9
J

Site #2: Tarboo Creek - Absence

I

I
0

\

\

I
Site #2: Tarboo Creek Land Use

Legend

C==1 Buffer (2.3 Km)
EJ Agriculture
Ill industrial
• ,.

I

,

0.20%

I

t

Residential

57

OA{Jriculture

a Undcvelo~d

Figure 10

.

,.

Lake St. Clair - Absence

..

-.

0

·~
.~

-- ••

.. .

-....

.

.

.,

.

'
)

,,,.
p

,,,...

...

-

.

l

r-

'I

. . ..

~

f.

. ,., .
.
......

I ..·

;-

.

Site #3: Lake St. Clair Land Use

2.80%
8.20%

__

.,,_

a Indu str ial
□ Re sidential

Agriculture

□ Agricultu re
□ Undeveloped

Industrial
Residential

I •

58

Figure 11


Site #4 : Crocke r Lake - Presence

I

~-

i

/

/

•1

I

I

--~~-

·\

I

• ,,.

,



I

...

0

\

I

I'

..
Site #4: Croclwr L .:i kc Land Use

Legend

1.1m05%

~ Buffer (2.3 Km)

c:=J Agriculture

c Industrial
0 Residential

~

Industrial
Residential

59

0 AgrtCulture

a Undev~klpcd

Figure 12

Pf-~,.
Site #8: Wye lake land Use

,

,.

0.40%

..

.i
a Industr ial
D Residential
□ Undeveloped

::

Site #8: Wye Lake - Presence

..

.0

..

...."

•... :-

~

ite #5: Koenaman Lake - Absence
.

,

I

•I . .

0

..
'.

Legend

Site #5 : Koenaman Lake Land Use

c:=J Buffer (2.3 Km)

r

-;c=J Agricultu re

,

a fndu::tri:11
o Residential
c Undevelo ped

Industrial_
Residential

60

Figure 13

Site #6: Nisqually Lake - Unable To Determine



\

Site #6: Nisqually Lake Land Use

-.....Legend -~

(I\ l□Unde,eJopedl
~

~ Buffer (2.3 Km) l'
Agriculture

Ill Industrial

,.

Residential

61

Figure 14

..'

-:ti.,



._a -, • •

~

-.

...

••

I

._. l.,..h .

:.:!

Site·#7:
l'Allderson
Lake - Presence
L•
._

.. • •. It:
I

'

0

.

,.
a ••





I•

\

'
\

Site #7: Anderson L a ke Land Use


Industrial

0 Residential
0 Agricu lture
0 Unde ve loped

91 .80%

L_e_g_e-nd
-

---,•
(

~ Buffer (2.3 Km)
Agriculture
. . . Industrial
Residential

62

p

Figure 15

••
Site #9: Oak Patch Lake - Presence

...

0

\

.......
\

\

\

\

..

.
)

Legend

Site #9: Oak Patch lake Land Use
0.10%

[=i Buffer (2.3 Km)
[TI Agriculture



Indu strial

□ Undeveloped

Industrial
Residential

63

Figure 16

I

•.

Site #13: Fagan & McEniiery Lake - Absenc~r

..

_.
~

/

r

i

,

.

I

.,:Y

;f.
itr

-

., .
r

--I:
J

. _.



,

S ite #13 : Fagan & M c Enni ery Lakes

La n d Use

Legend
0 Indus trial
D R csidenlial
0 Ag ricultute
□ Undeveloped

c=J Buffer (2.3 Km)
CJ Agriculture "1
Industrial

64

1

I

I ~ U I 'I.,

I

I

/

\

I

I
I

~~iii..,

(
\

\

~

\

'.
-~-

0

.d..

...

I

I
I

-...
'\,

Site #14: Ranger Lake Land Use
0.50%

Legend

1

a Industrial

[:=J Buffer (2.3 Km)

0 Rcsktcnlial
aAg,iculturo

CJ Agriculture

a Undeveloped

1111 Industrial
Residential

.I

65

,,.

Figure 18



.

.. .,. .,

,.

P••

II

"J J

Site #16: Beaver Lake .. Absence

___..---

-----

Q

...



I

I

I
I

i

..

I

I

. . ..P!

I \
·• \ I

-· ir:

D

r~-_ ~

.~.
... .

lp.,

· ,=I :.

lo

.:fr.
1

---~ ~-

. :-w . .-

.,

J..•

..
. •.
.. f

...._.
4~ ,.·
!"I

-~.- . ."'.. .. ·. ...
.

~ -

-

~ _.,,.,,...
..

.;a.

-!--------"'

~

J

~

Site #16 : B eaver L ake - Lan d Use

I~

~


2.60%

- ~

' Buffer (2.3 Km)
Agriculture
Industrial
Residential



••

66

□ Industrial
0 Residential
0 Agriculture
0 Undeveloped



Figure 19

Site #20: Carson"~ ke - Absence ,
~

...

__

-.......~

•.
/

/

. .

·-

.
"' .
I

I



-

0

\

,,_-..

Site #20: Carson L ake Land Use

Legend
• ~ Buffer (2.3 Km)
a lndu:.trbl

CJ Agriculture

o Rc~idt!nli:,I

a Undcvclo ed

Industrial

r

Residential

-·..

I

67

Figure 20

. 'I;. .. .

Site. #22: Bear & Porter Creek - Unable To Determine



.,.
·~I •



(


J

Site #22: Bear Creek & Porter Creek
Land Use

Legend

~D
~

0.02%"'\; 0.06%

Buffer (2.3 Km)
□ Industrial

Agriculture

□ Ag ricu ltu re

• 1111 1ndustrial

□ Undeveloped

99.92%

Residential

68

I

,.





Site #23: Our l at<e - Absence

...

-

..

-

- ---------------~-~
',,

-tr 1'6"••

••

-I..

_,

D.

II

lr

I

.

.

wj
.

,._

..

Site #23: Our L a k e - La nd Use

r=J Buffer (2.3 Km)

0 Industrial
0 Residential
0 Agriculture

[L8 Agriculture

D Undevelop_ed

Industrial
Residential

69

r

.-, sfte #23: Our L:'a lra - Absence

-

ff' .f·. .,J.:l ______
.---

-



--------~

~

/



. .fa,,'••

e.

J

r

~

j;!'.".'{ ~ ::

!J,f't'

1

.....

,. -

r •

r

....

-L.,
!



.

/
/

I



-..

.-...,~--&sr..-ir:a'.t::~~~-M~~
. ._
r_

1 I

Site #23: Our L a k e - L and U se

·------- -------------

8.40%
0.60%

.· ~-- -;. Lege~d

C:=J Buffer (2.3 Km)

0 Industrial
0 Residential
0 Agricu lture
□ Und ev~~e~

~- --

[::J Agriculture

11111 Industrial
Residential

69

Figure 22

Sile #2S: Echo Lake
- Presence
.
_.-· ,,.,,.. -

.,,.,-•'

...

----

-

--

/'

'

.

'\
\

\

\

..

I

!'.!

\

I

\\

/

J

,'

J

I

J.

,,
Sito__..,..--;r
#2'i·.-Eccho
,.- Lake Umd U
.-----se

-

------1-.40%

0.80%

[=i Buffer (2.3 Km)

C::J Agriculture
Industrial

97.70%

Residential

70

0.10%