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Title
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Factors Affecting the Success of Pigeon Guillemots on Whidbey Island, Puget Sound, Washington, During the 2009 Breeding Season
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Date
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2012
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Creator
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Kreamer, Kirsten A
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Subject
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Environmental Studies
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extracted text
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Factors affecting the success of Pigeon Guillemots on Whidbey
Island, Puget Sound, Washington, during the 2009 breeding
season.
By
Kirsten A. Kreamer
A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
December 2011
© 2011 by Kirsten A.Kreamer. All rights reserved.
This Thesis for the Master of Environmental Study Degree
by
Kirsten A. Kreamer
has been approved for
The Evergreen State College
by
__________________________________
Erik V. Thuesen, Ph.D.
Member of the Faculty, Zoology
__________________________________
Ralph Murphy, Ph.D.
Member of the Faculty, Political Economy
___________________________________
Phyllis Kind, Ph.D.
Project Supervisor, Island County Marine Resources Committee
___________________________________
Date
Abstract
Factors affecting the success of Pigeon Guillemots on Whidbey
Island, Puget Sound, Washington, during the 2009 breeding season.
Kirsten A. Kreamer
Pigeon Guillemots (Cepphus columba) are colonial alcids that breed along
the western coast of North America, extending from Alaska to California.
While previous studies of breeding Pigeon Guillemots have taken place in
remote areas, the current study investigated five colonies of Pigeon
Guillemots on Whidbey Island, WA from 22 June, 2009 to 18 August,
2009. Whidbey Island is populated by 58,211 residents, 29,000 of whom
live in rural areas, including beaches that are utilized by Pigeon Guillemots
as nesting sites. Physical characteristics of burrows, feeding rates,
behaviors, numbers of adults and human disturbances were all recorded.
A total of 47 burrows were monitored, fifteen of which were determined to
have supported chicks to fledging weight, and were considered
successful. Burrow characteristics included size of entrance, type of
vegetation within 15 cm of entrance, distance of burrow entrance above
shore and distance of entrance from the top of the bluff. Human activities
were determined to be disturbances when Pigeon Guillemots displayed
agitated behaviors. None of the physical characteristics of burrows were
significantly correlated with success, nor were human disturbances.
Feeding rates were significantly correlated to success when all sites were
grouped together (ANOVA, p = 0.02), with significant results at the largest
site monitored (ANOVA, p < 0.01) Whidbey Island is an ideal location for
monitoring projects to continue throughout the year to determine seasonal
activities of Pigeon Guillemots. Further investigation on the success of
Pigeon Guillemots breeding within close proximity to human activities is
necessary to fully understand these complex interactions.
Table of Contents
Introduction
1
Study area and methods
3
Burrow characteristics
5
Feeding behaviors
6
Human disturbance
7
Results
7
Burrow characteristics
8
Feeding behaviors
9
Human disturbance
9
Natural history observations
10
Discussion
10
Feeding behaviors
10
Burrow characteristics
13
Human disturbance
14
Ecological implications
17
Conclusion
19
Literature Cited
39
iv
List of Tables
Table 1, Characteristics of colonies
21
Table 2, Burrow characteristics and weeks fed
22
Table 3, Feeding rates and weeks fed
23
Table 4, Study sites and weeks fed
24
Table 5, Human disturbance and weeks fed
25
List of Figures
Figure 1, Map of Whidbey Island and study sites
27
Figure 2, Mean entrance size for all burrows
28
Figure 3, Mean distance from top of bluff for all burrows
29
Figure 4, Mean distance from shore for all burrows
30
Figure 5, Types of vegetation surrounding all burrows
31
Figure 6, Mean rates of feeding for all burrows
32
Figure 7, Number of weeks fed for all burrows
33
Figure 8, Predated egg at the Mutiny Sands site
34
Figure 9, Predated juvenile at the Harrington North site
35
Figure10, Chick in burrow at the Harrington South site
36
Figure 11, Evidence of predation at Harrington South site
37
Figure 12, Successful chicks at the Mutiny Sands site
38
v
Acknowledgments
I would like to thank Erik V. Thuesen for his continued support and
encouragement, Ralph Murphy for his confidence in this thesis, and
Phyllis Kind for field support and patience. This project would not have
been possible without the support of the Whidbey Island Marine
Resources Committee, nor would it have come to completion without the
support of family and friends.
vi
Introduction
Auks are marine birds that reside north of the equator and utilize
shorelines as colonial breeding sites. Over 2 million pairs of Auks nest
along the coastline of North America (Kaiser and Forbes, 1992), using a
variety of nesting habitats, ranging from grassy slopes to bluffs. The
breeding success of Auks (Alcidae) has been influenced by human
disturbance (Pierce and Simons, 1986; Cairns, 1980; Drent, 1965), which
has been both direct and indirect: disturbances from researchers have
been directly correlated to nest abandonment by adults and marked
declines in fledgling success (Pierce and Simmons, 1986; Cairns, 1980;
Anderson and Keith, 1980; Carney and Sydeman, 1999). Indirect effects
of human disturbances include the introduction of species which did not
co-evolve with burrow-nesting species of birds (Jones et al. 2007;
Vermeer et al. 1993b).
Abundance of prey items utilized to provision chicks has been
correlated to success of Auks, as time spent foraging for prey items by
adults directly influences provisioning rates to chicks (Litzow and Piatt,
2003). Lipid content of prey items, as well as size of prey items delivered
to chicks have both been directly correlated to success of Auk chicks
(Anthony et al. 2000, Golet et al. 2000, Wanless et al. 2005).
Changes in climate and other factors have caused declines in
certain Auk populations (Kaiser and Forbes, 1992, Seiser at al. 2000), as
well as environmental pollutants (Agler et al. 1999; Litzow et al. 2002;
1
Seiser et al. 2000). The effect of environmental contaminants has been
well documented following the TV Exxon Valdez oil spill, which has been
directly correlated to the decline of five species of Auks breeding in Prince
William Sound, AK (Litzow and Piatt, 2003; Ewins, 1993; Golet et al. 2000;
Oakley and Kuletz, 1996).
Interspecific competition for nesting sites and availability of nesting
sites has been correlated to breeding success of Auks (Williams, 1975;
Nelson, 1987), as well as the physical characteristics of burrows used as
nests (Emms and Verbeek, 1989; Vermeer, 1979). Synchronized laying of
eggs among adults (Birkhead, 1977; Hatchwell, 1991) effect breeding
success, as well as the synchronized fledging of chicks (Hatchwell, 1975).
Pigeon Guillemots (Cephus columba) are semi-colonial alcids that
breed on coastlines or islands of western North America extending from
northwestern Alaska to southern California (Ewins, 1993). Breeding
populations of Pigeon Guillemots are also present in the eastern portion of
the Bering Sea, yet these populations have not been studied extensively
(Konyukhov, 2000). Breeding success of Pigeon Guillemots has been
studied in Alaska, British Columbia, Washington and California, with the
aid of blinds and not within direct vicinity of human inhabitants (Nelson,
1987; Nelson, 1991; Vermeer, 1993).
Previous studies of Pigeon Guillemots have been conducted on
islands, which support the largest breeding colonies of this species
2
(Ewins, 1993; Vermeer et al. 1993b). Islands have historically lacked
mammalian predators, and offer access to shallow foraging areas, which
enable breeding Pigeon Guillemots to provision more chicks than other
Auks. This ability to provision offspring results in two egg clutches as
opposed to a one egg clutch (Emms and Verbeek, 1991; Bradstreet and
Brown, 1985). Islands located in Puget Sound, Washington, not only
support breeding populations of Pigeon Guillemots, but are also inhabited
by humans.
The purpose of this study was to determine if physical
characteristics of burrows, feeding behaviors and anthropogenic
disturbances affected the breeding success of Pigeon Guillemots on
Whidbey Island, Puget Sound, WA during the 2009 breeding season. The
human population of Whidbey Island in 2009 was 58,211 with half of this
population residing in rural areas, including beaches and shorelines (2000
Census). Pigeon Guillemots utilize these shorelines that are easily
accessible to humans as nesting habitat, providing a unique opportunity to
observe behaviors and colony characteristics without the aid of blinds.
Study area and methods
Observations of five Pigeon Guillemot colonies were conducted on
Whidbey Island, Washington (48° 08’11” N, 122° 34’ 57” W) from 22 June,
2009 to 18 August, 2009. One site per day was observed over an interval
of five hours, during which number of adults, physical characteristics of
3
burrows, behaviors, disturbances, burrow activity and chick feeding
behaviors were all recorded. Pigeon Guillemot activity is highest at
colonies between dawn and mid-morning (Drent, 1965; Vermeer et al.
1993b) therefore five hour intervals were used to monitor the most active
periods of feeding and socializing. Observation periods began before
sunrise in order to monitor the arrival of adult birds and to obtain an
estimate of adult populations at peak attendance times (Vermeer, et al.
1993a). The five locations of study were Shore Meadows, Harrington
South, Harrington North, Rolling Hills and Mutiny Sands, and were located
on the southern, western and eastern portions of the island (Figure 1).
All colonies monitored were located in bluffs, where natural cavities
were used as burrows by Pigeon Guillemots. These cavities were
determined to be nesting sites or burrows when a prey item had been
delivered to that cavity. Pigeon Guillemot chicks fledge at night (Ewins,
1993) when observations were not conducted, therefore success of the
burrow was determined by using the number of consecutive weeks prey
were delivered to burrows. Pigeon Guillemots reach fledging weights
between 33-37 days after hatching (Thoresen and Booth, 1958), therefore
burrows receiving deliveries of prey items for five weeks or longer were
determined to be successful, indicating that the chick or chicks inside the
burrow had reached fledgling weight .
4
Burrow characteristics
Breeding success of Pigeon Guillemots has been correlated to burrow
structure (Emms and Verbeek, 1989) and concealment of the burrow
entrance (Emms and Verbeek, 1989). Breeding Pigeon Guillemots in
British Columbia avoided nesting near trees to evade predation (Ewins, et
al. 1994). It was assumed that burrow placement on the bluff may have
affected the ability of predators to gain access to eggs and chicks, as rats,
raccoons and other mammalian predators could potentially gain access to
burrows that were close to the tops of bluffs, as well as nests that were
formed in the roots of trees (Ewins, et al. 1994). All of the following
physical characteristics were recorded for all burrows at all colonies:
a. area of burrow entrance (cm²),
b. height of burrow entrance above shore,
c. distance of burrow entrance from top of bluff,
d. type of vegetation within 15 cm of burrow entrance,
Vegetation types were categorized into five groups: no vegetation,
grasses, shrubs, trees or roots. All distances were visual estimates;
burrow entrance areas were based on bird body length.
Two-way ANOVA (SAS/STAT 9.2, SAS Inc.) were used to test for
significant differences in the number of weeks fed based on physical
5
characteristics of burrows. This determined if any or all of the physical
characteristics documented were a function of success.
Feeding behaviors
Success of chicks has been significantly correlated to feeding rates
within the first weeks after hatching (Cairns, 1981; Cairns, 1987; Emms
and Verbeek, 1991), therefore careful observations of chick feedings were
recorded during each five hour observation period. Feeding rates were
calculated by summing total number of deliveries to individual burrows,
then dividing total number of deliveries by total number of hours observed.
Feeding rates were then compared to number of weeks fed to determine if
correlations existed between the two variables.
Pearson’s correlation (SAS/STAT 9.2, SAS Inc.) was used to test
for correlations between feeding rates and numbers of weeks fed.
Correlations were conducted twice: first on the overall data set and then
by site.
One-way ANOVA (SAS/STAT 9.2, SAS Inc.) was used to
determine if differences existed between number of weeks fed and site of
colony. This analysis was completed in order to determine if any of the
study sites was significantly different in the number of weeks fed.
6
Human disturbance
When disturbed, Pigeon Guillemots show agitation by sounding alarm
calls, taking off en masse, rapidly leaving an area as individuals, or
mobbing potential predators (Drent, 1965; Ewins, 1993; Nelson, 1985;
Nelson, 1987.) If these behaviors were exhibited as a result of
anthropogenic sources (dogs, boats, planes, etc.), the source was
determined to be a disturbance. This included observer arrival or
movements that caused changes in behaviors. Because all burrows
monitored were within colonies and not independent nesting sites, all
disturbances affected all nests within colonies.
One-way ANOVA was used to test the effects of human disturbance on
the number of weeks fed (SAS/STAT 9.2, SAS Inc.). This analysis
determined if a relationship existed between number of human
disturbances and number of weeks fed at all sites.
Results
A total of 47 burrows were observed on Whidbey Island during the
2009 breeding season. The number of burrows at each site was as
follows: Shore Meadows had eight burrows, Harrington South had seven,
Harrington North had nine, Rolling Hills had 15, and Mutiny Sands had
seven. Fifteen of these burrows received prey deliveries for five weeks or
more, indicating that chicks within these burrows reached fledging size
and were therefore successful. Shore Meadows had two successful
7
burrows, Harrington South had two, Harrington North had four, Rolling
Hills had six, and Mutiny Sands had one (Table 1). Burrows were
restricted to cavities formed in the bluffs; no other nesting habitat was
utilized by Pigeon Guillemots in this study.
Counts of adults arriving to colonies after dawn were counted to
obtain a total population of both breeding and non-breeding adult Pigeon
Guillemots. The numbers of adults present at colonies were: Shore
Meadows 70, Harrington South 32, Harrington North 48, Rolling Hills 51,
and Mutiny Sands had 52 (Table 1).
Burrow characteristics
Physical characteristics of burrows had no affect on Pigeon
Guillemot success for the 2009 breeding season (Table 2). Entrance size
of burrows had no affect on number of weeks fed (ANOVA, p = 0.50), nor
did distance of entrance from the top of the bluff (ANOVA, p = 0.62), or
distance of the burrow entrance from the shore (ANOVA, p = 0.67).
Vegetation type within 15 centimeters of the burrow entrance also had no
affect on success (ANOVA, p = 0.50). No site had distinguishing
differences in mean entrance sizes (Figure 2), mean height above shore
(Figure 3), or mean distance from the top of the bluff (Figure 4). Of the 47
burrows monitored, 24 had no vegetation within 15 cm of the entrance,
eight had grass, six had shrubs, nine had roots, and no burrows had trees
(Figure 5).
8
Feeding behaviors
No single site had significant differences in mean feeding rates
(Figure 6). Feeding rates were significantly correlated to success for the
entire dataset (Pearson’s correlation, p = 0.02) (Table 3). When sites
where looked at individually, only Rolling Hills, the largest site, had a
significant correlation between feeding rates and number of weeks fed
(Pearson’s correlation, p < 0.01). Correlations were not significant at the
Shore Meadows site (Pearson’s correlation, p = 0.09), at Harrington North
(Pearson’s correlation, p = 0.65), Harrington South (Pearson’s correlation,
p = 0.89) or at Mutiny Sands (Pearson’s correlation, p = 0.30) (Table 3).
A total of 47 burrows were monitored during this study, the majority
of which were fed for four weeks (Figure 7). The number of weeks fed by
site was not significantly different (ANOVA, p > 0.05); therefore one site
was not more likely to have successful burrows than another (Table 4).
This indicates that none of the observed sites was more likely to have
more successful burrows than the others for this study.
Human disturbance
Human disturbances had no affect on number of weeks fed
(ANOVA, p = 0.97, Table 5). There were also no significant results
between number of disturbances and site (ANOVA, p = 0.32) (Table 6).
This result indicates that no site in this study had significantly more
disturbances than any of the others. Numbers of human disturbances
9
were: Shore Meadows 11, Harrington South 12, Harrington North 15,
Rolling Hills, 15 and Mutiny Sands 61 (Table 1).
Natural history observations
Direct observations of nests revealed egg failure due to avian predation
(Figure 8), predation of a chick by an unknown predator (Figure 9), and a
burrow which failed, and had collapsed (Figures 10 & 11). Observations
also revealed that at least one burrow supported two chicks to fledgling
size (Figure 12).
Discussion
Feeding behaviors
Feeding behaviors were found to effect success when all burrows
were grouped together as well as for the largest site in the study. Feeding
rates and success were significantly correlated for all sites(Pearson’s
correlation, p = 0.02), as well as for the Rolling Hills site ( Pearson’s
correlation, p < 0.01).This was the largest colony with fifteen total burrows,
six of which were successful. Rolling Hills had nearly twice as many
burrows as the other colonies, which increase the chances of finding
significant relationships between variables. Therefore, the total grouping of
colonies gives a better insight as to the significance of feeding rates. The
average hatching weight of Pigeon Guillemot chicks is 41.5 g (Thoresen
and Booth, 1958), weight doubles five days after hatching, triples after 10
days, and chicks reach 411 g at fledging (Drent, 1965), which is reached
10
33-37 days after hatching (Thoresen and Booth, 1958). Pigeon Guillemot
chicks on Farallon Island aged 1 to 30 days after hatching were fed more
often than chicks aged 31 days and older (Nelson, 1987). This was also
observed in colonies in British Columbia, where delivery rates were
highest during the first half of the nestling period (Emms and Verbeek,
1991). In both studies, feeding then tapered off, due to the reduced need
for provisioning by older chicks, or as a strategy by parents to encourage
fledging (Emms and Verbeek, 1991). Black Guillemot (Cepphus grylle)
chick provisioning decreased markedly when chicks had reached 30 days
old (Peterson, 1981); these birds are closely related to Pigeon Guillemots
and have similar breeding behaviors (Cairns, 1981).
Rapid feeding events were observed during this study, with at least
two adults provisioning chicks at multiple burrows. Burrows receiving
deliveries from two adults were apparent as one adult entered the burrow
with a prey item, and was immediately followed into the burrow by a
second adult with another prey item. Drent (1965) observed that both
parents provisioned chicks, and these fast deliveries indicate that this was
also the case for Pigeon Guillemots on Whidbey Island. These rapid
deliveries could indicate that the chick or chicks in these burrows had not
yet reached an asymptotic weight which is reached between day 30 and
40 after hatching (Ewins, 1993). Feeding rates decline rapidly after this
asymptotic weight has been reached by the chicks and is indicative that
chicks are approaching fledging age (Ewins, 1993).
11
Lipid contents of prey items have been found to correlate positively
to Pigeon Guillemot success (Golet et al. 2000; Litzow et al. 2002).The
availability of prey items has also been positively correlated to
success(Litzow et al. 2002). A comprehensive study of colonial seabirds in
the North Sea in Scotland concluded that Common Guillemots (Uria
aalge) were particularly susceptible to low-quality prey items, as they
deliver one prey item at a time to chicks (Wanless et al. 2005). Pigeon
Guillemots also deliver one prey item at a time, and populations in Prince
William Sound, AK, were determined to have slow recovery rates after the
TV Exxon Valdez oil spill affected populations of oil-rich prey items (Litzow
et al. 2000). Populations of prey species were also heavily affected by the
climatic regime shift that occurred between 1976 and 1977 in the North
Pacific (Agler et al. 1999). Lipid contents were not measured in this study,
but may have affected growth rates and fledging success of Whidbey
Island colonies; adults that provision chicks with high-lipid prey items are
more likely to fledge two chicks, as opposed to one chick (Golet et al.
2000; Kuletz, 1986).
Specialization by adult Pigeon Guillemots also may have affected
chick success. Adults that selected one type of prey item to deliver to
chicks had higher success rates than those adults that did not specialize
in Prince William Sound, AK (Golet et al. 2000). This was not because
adults that specialized in prey selection chose higher-lipid prey items, but
because they selected larger prey items, allowing for fewer deliveries and
12
therefore fewer opportunities for predators to find burrows (Golet et al.
2000). Specialization was not examined during this study, as fishes such
as Eulachon (Thaleichthys pacificus) are very difficult to decipher from
Pacific Sand Lance (Ammodytes hexapterus), Surf Smelt (Hypomesus
pretiosus), and Crescent Gunnels (Pholis laeta) unless the researcher has
these prey items in hand. These species vary in lipid content from 20% in
Crescent Gunnels to 50% in Eulachon (Anthony et al. 2000), and
misidentification of prey items would lead to incorrect conclusions.
Burrow characteristics
Burrow characteristics have been shown to have significant effects
on success in previous studies in colonies of alcids (Emms and Verbeek,
1989; Vermeer, 1979; Vermeer et al. 1993b), yet no strong correlations
were found in this study. Burrow placement on the bluff was assumed to
have a possible effect on predation by mammals, as Pigeon Guillemots
utilize cavities that are inaccessible to mammalian predators (Ewins et al.
1993) yet there were no significant correlations between variables
recorded and number of weeks fed. Pigeon Guillemots have been noted to
nest in a variety of materials, including discarded pipes and nest boxes
(Nelson, 1987) tires, empty buildings, ferry terminals, root balls,
abandoned nests of other seabirds and rabbits, driftwood piles (Ewins,
1993), and old bomb casings (Speich and Wahl, 1989). All burrows
included in this study were cavities in bluffs, and no burrows had trees
13
near the burrow entrance, which both indicate that presence of
mammalian predators were a factor in nest site selection.
Thermoregulation of burrows could have a significant effect on
chick development on Whidbey Island. Drent (1965) observed that adult
Pigeon Guillemots brooded chicks longer in cooler weather, exposing
themselves to greater chances of predation. Conversely, Black Guillemot
chicks suffered an increase in mortality rates from 2% in 1975 to 11% in
1977 due to heat (Asbirk, 1979). Stable microclimates reduce energy
expenditures for parents, increasing foraging opportunities for prey items
and increasing chances of survival for chicks (Kaiser and Forbes, 1992.)
Regulated temperatures within nesting materials could eliminate the risk of
both cold temperatures and overheating, and could be a factor for
selection of nesting sites as well as success rates.
Human disturbance
Human disturbances have been shown to have adverse effects on
breeding colonies of birds that frequently nest near human habitations
(Carney and Sydeman, 1999). It is, however, possible that interactions
with humans do not affect Pigeon Guillemots in an adverse way on
Whidbey Island. The populations monitored during this study may have
been able to adapt to human interactions more readily than populations
previously studied. Laysan Albatross (Diomedea immutabilis) adults and
chicks that were frequently visited by humans were less aggressive than
14
those that were not visited, indicating that interactions had decreased
sensitivity to human disturbances (Burger and Gochfeld, 1999). This
phenomenon may be occurring on Whidbey Island with Pigeon Guillemots
that are frequently exposed to human disturbances.
It is also possible that observer influence had a greater effect than
realized or reported during this study. Because sites were monitored once
a week, birds may not have had time to acclimate to a constant presence
of a human, and burrows may not have been provisioned while the
researcher was present. Use of blinds could have eliminated this
distraction for the breeding Pigeon Guillemots. Tufted Puffin (Lunda
cirrhata) success on Barren Island, Alaska was reduced from 94% (15
fledglings from 16 eggs laid) to 18% (6 fledglings from 34 eggs laid) based
solely on disturbances caused by researchers (Pierce and Simmons,
1986). Tufted Puffins left nests for longer periods of time in the highly
disturbed area, exposing chicks to inclement weather, and longer periods
between feedings (Pierce and Simmons, 1986).
Human presence may have had an indirect effect on success, as
some predators of Pigeon Guillemots are commensal with humans. Rats
(Ratus spp.) prey on eggs, chicks and adult Pigeon Guillemots and are
responsible for seabird population declines (Atkinson, 1985). Burrow
nesting alcids are believed to be particularly at risk from rat predation, as
rats frequently forage for food and build nests in crevices, which Pigeon
Guillemots use as nests (Jones et al. 2007). Invasive species are
15
considered to be the largest terrestrial threat to seabird colonies (King,
1985); this was supported by a study in British Columbia, which found that
non-native Raccoons (Procyon lotor) were the main predator of Pigeon
Guillemot eggs and chicks (Vermeer et al. 1993b). Northwestern Crows
(Corvis caurinus) have been documented to follow researchers and later
prey upon chicks that had been examined by humans (Vermeer et al.
1993b). Evidence of predation was found at Mutiny Sands, Harrington
North, Harrington South and Shore Meadows. A predated egg was found
at Mutiny Sands, most likely from an avian predator (Figure 8). A wing
from a juvenile Pigeon Guillemot was found at the Harrington North site
(Figure 9), and an easily accessible burrow at the Harrington South site
was also predated (Figures 10 &11). None of these predations were
witnessed by the observer.
Predation has been deterred by synchronized breeding in alcids, as
adults will group together and mob potential predators (Williams, 1975).
Chicks that fledge in groups are also more likely to survive than single
chicks fledging alone (Williams, 1975). Synchronized breeding is likely to
have occurred at the Harrington North site, as no burrows at that site
received deliveries after 29 July, 2009, a full two weeks before burrows at
other colonies stopped receiving deliveries. Other colonies in this study
may have also been synchronized, but not as clearly as the Harrington
North colony.
16
Ecological implications
The small number of successful burrows during the 2009 season
leads to several possible explanations: the breeding population of Pigeon
Guillemots on Whidbey Island for that season was affected by unobserved
variables, observations for the season did not start early enough and the
reported number of burrow receiving deliveries is incorrect, or success
should have been measured by a variable other than number of weeks
fed. It is also possible that 2009 was an extreme low in reproductive
success for Pigeon Guillemots at these colonies.
Research for this project commenced on 22 June, 2009, and
deliveries of prey items were already taking place at all five colonies; this
indicates that some of the burrows may have been receiving deliveries for
longer periods of time than reported, and more than fifteen total burrows
were successful. Seventeen burrows were recorded to have been fed for
four weeks (Figure 7); eight of which had been receiving deliveries during
the first week of observation. Correlations between early laying times and
success have been reported for Pigeon Guillemots, as well as other alcids
(Asbirk, 1979; Cairns, 1981; Divoky, 1982; Drent, 1965; Ewins, 1993)
Adults that breed later are typically inexperienced, have lower success
rates, and do not lay as many eggs (Ainley et al. 1990; Asbirk, 1979). It is
possible that successful nests that started earlier in the season were
determined to be unsuccessful, and the majority of observations were on
burrows that were utilized by inexperienced adults. Because research for
17
this study began after eggs had been laid, and in some cases, after chicks
had hatched, it is difficult to report with certainty that success was
determined accurately due to the timing of the project.
Pigeon Guillemots utilize natal cavities for rearing chicks (Drent,
1965; Nelson, 1991); if natal cavities are not available, males will secure
burrows within 200 m of natal sites (Nelson, 1991). This site fidelity
indicates that the adults present at each colony were likely hatched within
close vicinities of that colony, and could indicate past success of the
colony as a whole. In order for populations of Pigeon Guillemots to remain
stable, 40% of chicks must survive to breeding age (Nelson, 1991).
Breeding Pigeon Guillemots pairs fledge an average of one chick per
season (Nelson, 1991); this study found that 15 burrows supported chicks
to fledgling weights, which falls far below the required 40% needed to
sustain the population. It is evident by the number of breeding and nonbreeding adults present at all colonies that Pigeon Guillemots have been
successful in the past and that the 2009 season may have had unusually
low success rates. It is also possible that this study did not begin early
enough in the season to accurately account for all feedings to all burrows;
2009 was an unusually warm year for Whidbey Island, and nesting could
have begun earlier than previous seasons, when observations were not
taking place.
18
Conclusions
A total of 47 burrows were observed during the 2009 breeding
season on Whidbey Island; 15 of which were determined to be successful
based on number of weeks fed. The implications of this low number are
not consistent with the numbers of adult Pigeon Guillemots that were
observed during this study. The number of adults within the five colonies is
indicative of successful breeding seasons in previous years, as Pigeon
Guillemots return to natal nesting sites during the breeding season (Drent,
1965; Nelson, 1991). Of all factors observed, significant correlations were
found between number of weeks fed and feeding rates for one site, Rolling
Hills (Pearson’s correlation, p < 0.01), and when all sites were analyzed
together (Pearson’s correlation, p = 0.02). No other significant correlations
were found, which indicates that success may have been a function of
unknown variables. It is also possible that Pigeon Guillemots began the
breeding season earlier than usual in 2009, before this study commenced.
Whidbey Island is a unique habitat in which to study Pigeon
Guillemot breeding biology; burrows are accessible to researchers, and
human interactions are prevalent. The ease of access to colonies on this
island provides opportunities for future research projects, exploring
variables that were not looked into for this study. Burrow characteristics
including complexity of the inner cavity, and thermoregulation of burrows
could be looked into, as well as the substrate composition of the bluffs.
Other possible projects include type of prey and lipid rates of prey items
19
delivered to chicks using mist nets, and the banding and tracking of adults
to determine fluctuations in attendance and site fidelity. Further research
is needed on this island in order to determine definitively if success rates
of these populations of Pigeon Guillemots differ from conspecifics nesting
on uninhabited islands. Year round monitoring of Pigeon Guillemots on
Whidbey Island could provide insight into seasonal behaviors, changes in
population throughout the year, and patterns in breeding characteristics.
Future studies should be conducted on one colony, starting earlier in the
season with observations taking place daily with the use of a blind, and
continuing for consecutive seasons. Further investigation on the success
of Pigeon Guillemots breeding within close proximity to human
developments is necessary to fully understand these complex interactions.
20
Table 1. Characteristics of Pigeon Guillemot colonies on Whidbey Island in 2009.
Number of all active burrows, successful burrows, number of adults present, and
number of human disturbances for each colony.
Site
Burrows
(n)
Successful
Burrows (n)
Adults (n)
Human
Disturbances (n)
Shore
Meadows
8
2
70
11
Harrington
South
7
2
32
12
Harrington
North
9
4
48
15
Rolling Hills
15
6
51
15
Mutiny Sands
8
1
52
61
Totals
47
15
253
114
Mean
9.4
3
50.6
22.8
Standard
Deviation
3.2
2
13.5
9.6
21
Table 2. Summary of results using two-way ANOVA, examining differences
between number of weeks fed and physical characteristics of all monitored
burrows of Pigeon Guillemots on Whidbey Island.
Characteristic
n
Mean ± SD
Entrance size cm²
47
324.47 ± 354.43
Distance from bluff top (m)
47
2.40 ± 3.83
0
18.3
2.8 1 0.6
Height above shore (m)
47
9.25 ± 4.80
3.1
21.3
2.7 1 0.6
Vegetation
47
n/a
n/a
n/a
2.8 1 0.5
Min
Max MSE F p
24.0 2230.0 2.6 1 0.5
22
Table 3. Correlations coefficients (R) between number of weeks fed and mean
feeding rates of Pigeon Guillemots on Whidbey Island, for all sites combined and
as single units
Site
Shore Meadows
Harrington
South
Harrington
North
Rolling
Hills
Mutiny
Sands
All
Sites
n
8
7
9
15
8
47
R
0.63
-0.06
0.18
0.66
0.63
.34
p
0.09
0.89
0.65
<0.01
0.09
0.02
23
Table 4.Colonies of Pigeon Guillemots on Whidbey Island showed no differences
in weeks fed and site. Results of one-way ANOVA revealed no significant
differences (p > 0.05), as no site was fed for a longer or shorter amount of time
during this study.
Number of
Burrows
MSE
df
F
p
47
2.62
4,47
0.07
> 0.05
24
Table 5. Success of Pigeon Guillemots on Whidbey Island was not affected by
human disturbances. Results of one-way ANOVA test to find differences between
total number of disturbances and total number of weeks fed revealed no
significant differences (p = 0.9656). Results indicate that no site in this study had
significantly more or less disturbances than any other site.
n
df
MSE
F
p
47
3,3.43
2.564
0.09
0.9656
25
Table 6.The five colonies of Pigeon Guillemots studied on Whidbey Island did not
vary significantly in number of human disturbances. Results from two-way
ANOVA show that no site had a significant difference in disturbances (p =
0.3156).
Numerator DF
Denominator DF
F
p
4
713
1.19
0.3156
26
Figure 1. Map of Whidbey Island showing the sites where Pigeon Guillemot
colonies were studied. Inset shows the location of Whidbey Island within the
Puget Sound.
27
Figure 2. Mean entrance size (± SD) for burrows of Pigeon Guillemots at all
colonies on Whidbey Island (n = 47). No single colony had significantly different
entrance sizes (ANOVA, p = 0.5). The greatest variation existed within the Shore
Meadows site, and the least in the Mutiny Sands site. Study sites are shown in
Figure 1.
28
Figure 3. Mean distance of all Pigeon Guillemot burrows (n = 47) from top of bluff
(± SD) on Whidbey Island. No colony displayed significant differences in distance
from the top of the bluff in which burrows were located (ANOVA, p = 0.6). Study
sites are shown in Figure 1.
29
Figu
re 4. Mean distance of all Pigeon Guillemot burrows (n = 47) above the shore in
meters (±SD) on Whidbey Island. No colony had burrows that were significantly
different in height (ANOVA, p = 0.6).The Harrington North site had the most
variation. Study sites are shown in Figure 1.
30
Figure 5. Types of vegetation within 15 cm of Pigeon Guillemot burrow entrances
for all monitored burrows on Whidbey Island. Twenty four burrows had no
vegetation, nine had roots, eight had grasses, six burrows had shrubs, and no
burrows had trees near the entrance. Study sites are shown in Figure 1.
31
Fig
ure 6. Mean feeding rates (± SE) for all colonies of Pigeon Guillemots on
Whidbey Island. Rates were obtained by dividing total number of deliveries by
total hours observed. No site was significantly different in feeding rates from
other sites (ANOVA, p = 0.5). Study sites are shown in Figure 1.
32
Fig
ure 7. Number of weeks fed for all Pigeon Guillemot burrows at all sites on
Whidbey Island. Study sites are shown in Figure 1.
33
Figure 8.Pigeon Guillemot egg shells at the Mutiny Sands site on Whidbey
Island. Egg shell on the right was predated by a bird, apparent by the opening at
the top and the residue left in the shell. Egg on left was broken open by hatching
chick; no residue was left in the shell, and it was no longer intact. Study sites are
shown in Figure 1.
34
Figure 9. Evidence of predation of a chick at the Harrington North site on
Whidbey Island. This is a wing from a juvenile Pigeon Guillemot, apparent by
downy feathers and lack of distinct coloration. Study sites are shown in Figure 1.
35
Figure 10. Pigeon Guillemot chick photographed inside the burrow at the
Harrington South site on Whidbey Island on 14 August, 2009. Chick is located in
the center of the photo, covered in black down. Exact age of chick is unknown.
Study site is shown in Figure 1.
36
Figure 11. The same Pigeon Guillemot burrow as in Figure 10, four days later on
18 August, 2009 on Whidbey Island. Chamber had collapsed and deliveries had
ceased; this was believed to be a predated nest.
37
Figure 12.Two Pigeon Guillemot chicks at fledgling age resting within a burrow at
the Mutiny Sands site on Whidbey Island. This was the single burrow at this site
to have deliveries of prey items for five weeks, and the only successful burrow at
the Mutiny Sands site.
38
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