PIGEON GUILLEMOT ABUNDANCE AND PREY COUNTS IN THE PUGET SOUND

Item

Title
Eng PIGEON GUILLEMOT ABUNDANCE AND PREY COUNTS IN THE PUGET SOUND
Date
Eng 2021
Creator
Eng Stocks, David
Identifier
Eng Thesis_MES_2021_Stocks
extracted text
PIGEON GUILLEMOT
ABUNDANCE AND PREY COUNTS
IN THE PUGET SOUND

By
David Alexander Stocks

A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
June 2021

© 2021 by David Stocks. All rights reserved.

This Thesis for the Master of Environmental Studies Degree
By
David Alexander Stocks

has been approved for
The Evergreen State College
By

___________________________________
John Withey, Ph.D.
Member of the Faculty

June 4, 2021
Date

ABSTRACT

Pigeon Guillemot; Abundance and Prey Counts in the Puget Sound
David Alexander Stocks
This thesis research explores the abundance and prey counts of 36 Pigeon
Guillemot colonies in the Puget Sound located in two regions, the South Sound Puget
Sound and on Whidbey Island. The data utilized were collected from 2015-2020 by two
citizen science organizations, the Whidbey Island Audubon Society, and the Nisqually
Reach Nature Center. The primary research question was whether prey types observed
being given to Pigeon Guillemot chicks, had any correlation with the next year’s colony
abundance. Individual colony abundance were also correlated with each other (in each
region) to assess population synchrony. The results of the analyses performed here did
not provide evidence for or against theories discussed within this thesis, primarily the
high and low lipid theory and the junk-food hypothesis.
Exploring trends over time in the two regions there was no linear trend to the
abundance of South Sound, while Whidbey Island has a slight increase in their
abundance. In the two regions gunnel was the most observed prey with South Sound
(69%) of observed prey being gunnel, and Whidbey Island (50%). Neither region showed
any correlation between abundance counts or prey types. Neither region demonstrated
synchronous changes across the colony abundance counts.

Contents

List of Figures ................................................................................................................................. v
List of Tables ................................................................................................................................. vi
Chapter One: Introduction .............................................................................................................. 1
Chapter Two: Literature Review .................................................................................................... 4
Marine Birds as Sentinel species ................................................................................................. 4
Natural History of Pigeon Guillemot .......................................................................................... 6
Threats to Pigeon Guillemot abundance ..................................................................................... 7
Prey base ..................................................................................................................................... 8
Breeding Biology ...................................................................................................................... 10
Citizen Science Organizations .................................................................................................. 12
Abundance Counts .................................................................................................................... 19
Prey Counts ............................................................................................................................... 19
Data Analysis ............................................................................................................................ 19
Regional analysis....................................................................................................................... 19
Colony-Level Analyses ............................................................................................................. 20
Chapter Four: Results ................................................................................................................... 21
Abundance Counts .................................................................................................................... 21
Prey Counts ............................................................................................................................... 21
Synchrony Analysis................................................................................................................... 25
Chapter Five: Discussion .............................................................................................................. 26
Bibliography ................................................................................................................................. 31
Appendix 1: South Sound Prey Count Dynamics ......................................................................... 36
Appendix 2: Whidbey Island 2 Prey Count Dynamics ................................................................. 38

iv

List of Figures
Figure 1: Timeline of organizations joining surveying of Pigeon Guillemot in the Puget Sound.13
Figure 2: A typical breeding season survey for Pigeon Guillemot. The top section focuses on
abundance while the bottom (“Burrow Activity”) section focuses on prey county. .................... 14
Figure 3: The colonies of South Sound......................................................................................... 16
Figure 4: The northern colonies of Whidbey Island ..................................................................... 17
Figure 5: South Sound and Whidbey Island annual abundance. The 5-year total is the sum of the
counts in each region for the 5-years (2015-2020) used in this study. ......................................... 21
Figure 6: South Sound total prey counts. See appendix 1 for yearly prey diversity breakdowns.
69% of all prey was gunnel. χ²10 = 49, p < 0.001 showed the prey type varied significantly from
year to year. ................................................................................................................................... 22
Figure 7: Whidbey Island total prey counts. See appendix 2 for yearly prey diversity
breakdowns. 50% of all prey was gunnel. χ²10 = 144, p <0.001 showed the prey type varied
significantly from year to year. ..................................................................................................... 23

v

List of Tables
Table 1 Wet mass energy density values of four common prey types for Pigeon Guillemot in the
Puget Sound. Based on Table 1 from Litzow et. al., (2002) ........................................................... 5
Table 2: South Sound Colony Results. The regression coefficient column is from simple linear
regression of colony abundance with you (2015-2020. Correlation columns show Kendall’s Tau
of colony abundance with prey counts (Total, Sculpin, and Gunnel) from the previous year
(2014-2019). Significant correlations are marked in bold with *. In correlation results, n/a
represents missing prey count data. .............................................................................................. 23
Table 3: Whidbey Island Colony Results. Linear Trend represents simple linear regression of
colony abundance from 2015 to 2020. Kendall’s Tau correlation of colony abundance with prey
counts (total, sculpin, and gunnel) from the previous year, 2014 to 2019. Those results with
significance are marked in bold with *. Those results in bold show a correlation. ...................... 24
Table 4: Synchrony Analysis of Pigeon Guillemot abundance from each colony per region. There
are no statistically significant results. ........................................................................................... 25

vi

Acknowledgements

I want to say thank you to the Nisqually Reach Nature Center and its science director
Terence Lee the center’s science director. Terence has been active in his support of my work
allowing me to have access to his data and his expertise while I have learned the ends and outs of
Pigeon Guillemot. It has been an educational experience to volunteer with him and help with the
data collection process, primarily with giving me the chance to keep my GIS mapping skills
honed. Thank you also to the MES director and my reader, John Withey, for his insights and
timely responses to my many questions while we worked on my thesis. His help with R cannot
be understated.

vii

Chapter One: Introduction
The Puget Sound is a dynamic and important marine environment for the Pacific
Northwest. Not only does it contain a wide range of biodiversity it also functions as an important
hub for travel. The Puget Sound is home to over 3,000 invertebrates and 200 marine fish,
including 8 species of salmon (National Wildlife Federation, 2020). There are twenty-six species
of kelp alone in the Puget Sound along with seagrass. Over 172 marine birds frequent the Puget
Sound with 72 species being highly dependent upon it as a food source and breeding site,
including the Pigeon Guillemot (Gaydos & Pearson, 2011). The Pigeon Guillemot is highly
dependent on the Puget Sound due to the species’ year-round residence, depending entirely on
the Puget Sound for both habitat and food.
The study of such a rich region is important for the continued conservation and
management of the Puget Sound. Approximately 4.2 million people live along the Puget Sound
coastline (Puget Sound Regional Council, 2020). This makes the conservation and management
of the Puget Sound important from an economic, environmental, and public health perspective.
To accomplish successful management of the region requires studies of a wide range of topics,
which is a daunting task requiring not only governmental, scientific, and academic institutions
but the utilization of citizen scientists. The work done with the Pigeon Guillemot is a good
example of how to utilize the resources of the community to accomplish a wealth of data
collection and to coordinate that data with a wide range of organizations. The marine
enviornment is a difficult but nevertheless important region of our earth to study for conservation
and basic science.

1

The process of taking yearly surveys over many years is a important to establish a
baseline for the abundance of Pigeon Guillemot. Conservation and avoiding future loss of
biodiversity requires a baseline to direct conservation in the best direction for the overall health
of the environment (Bull et. al., 2014). Thoughtful conservation planning requires data analysis
and long-term observation to ensure that actions create the desired effects, and the ability to
examine those results over time. By utilizing systemic surveys many species can be evaluated
and tracked through citizen-based activity.
One of the primary difficulties when it comes to surveying marine birds is acquiring an
accurate count of abundance. A winter survey of Pigeon Guillemot is conducted by airplane
during the winter months when they travel to the northern side of the Salish Sea (Gaydos, et. al.,
2011), but many colonies are counted by various organizations throughout the Puget Sound
during their breeding season (April to September). As a burrow nesting bird, the opportunity to
count breeding adults in their burrows can be difficult and like other members of the Auk family,
primarily the Black Guillemot and the Atlantic Puffins, it can be difficult to discriminate
between breeding pairs and non-breeding adults (Cairns, 1979) as they are monomorphic. Nonbreeding adults tend to leave the colony for extended periods throughout the day, usually
returning at first light while the breeding pairs can spend much of their time away from the
colony also, returning when the tide is high and the opportunity to successfully forage has
decreased. Mixing of juveniles can occur between colonies that are in proximity of one another
adding to the difficult of successful abundance counts. With the current members of a colony
spending much of their time away from the colony the understanding of the tidal impacts along
with the forage habits of an individual colony are important factors. To complete those counts,

2

volunteers depend on visual counts as visual count are key to successfully surviving hole-nesting
Auks (Cairns, 1979).
Pigeon Guillemots themselves spend a large amount of their time perched near the
colony’s nests, limiting their time interacting with the burrows themselves except when feeding,
to reduce predation (Bishop, et. al., 2016). They generally have a large percentage of nonbreeding adults and juveniles who spend a mixed amount of time both on the water and within
the area of the colony itself (Drent, et. al., 1965). Like the Black Guillemot, the Pigeon
Guillemot has a morning and evening peak in its colony attendance, which provides a good time
of day to perform visual counts. For the Salish Sea this morning peak is typically 8:00 - 9:00 am
(Terence Lee, pers. comm.). While one cannot control all the factors to make this the most
optimal time for surveying such as inclement weather, disturbances (both manmade and natural),
tidal shifts, or predation, weekly counts help to develop an overall abundance estimate. As a sixyear survey study suggested (Bishop, et. al., 2016), the highest number of birds seen at any one
time can be taken as the maximum for the colony in which they have been counted. Multiple
counts are taken throughout an hour-long survey and those surveys generally happen over the
Pigeon Guillemot three-month breeding period (Bishop, et. al., 2016). The surveys have been
conducted in Puget Sound by citizen scientists for 16 years. Originally the surveys started with
the Whidbey Audubon Society, but four other Audubon Society groups and the Nisqually Reach
Nature Center now also participate. In 2020, the Washington State Department of Fish and
Wildlife (Department of Fish and Wildlife, 1970) joined to curate this survey data, utilizing
Geographic Information Systems (GIS) and Survey123 to collect this data. The data from the
surveys is also being utilized by University of Washington for studies on the connection between
Pigeon Guillemot numbers and tidal to their chicks, tidal heights, and disturbances to the colony.

3

Chapter Two: Literature Review
Marine Birds as Sentinel species
Marine birds serve as an invaluable indicator of various factors in their environment.
Seabird data has provided insights into not only the study of climate change but also changes in
the marine ecosystem (Piatt et. al., 2007). The study of one species can provide a look into a
much larger range of subjects. A species like the Pigeon Guillemot that focuses upon specific
fishing stocks can show a decline or increase in said stocks as their prey choices shift. A Pigeon
Guillemot colony that primarily feeds off sculpin (Cottoidea) that suddenly shifts to feeding on
sand lance (Ammodytidae) could reveal a decline in their common foraging area or a general
change in their feeding habits. The Pigeon Guillemot is an important sentinel species for the
Puget Sound/Salish Sea area as it lives in the region year-round and is sensitive to environmental
factors such as water temperature, pollutants, and rising sea levels. By maintaining surveys on a
wide range of colonies within the Salish Sea scientists can monitor other far-reaching factors.
The Washington State Department of Fish and Wildlife and the Puget Sound Partnership
recommend the expansion of Pigeon Guillemot monitoring to provide more data on their diet and
reproduction due to their importance to the Puget Sound ecosystem (WDFW, 2013). By creating
an expansive database on the Pigeon Guillemot over multiple years any notable shifts in their
abundance could hopefully influence policy made in conservation management in the Puget
Sound. The collection of this data will largely rest upon citizen scientists within the communities
of the Puget Sound with the support of both academic, governmental, and conservational experts.
One of the main influencers on Pigeon Guillemot abundance is the prey upon which the
Pigeon Guillemot sustain themselves and the growth of their chicks from year to year. The
choices that an adult makes while feeding their chicks have a large impact on survival and
4

growth rates. Pigeon Guillemot tend to forage in established fishing areas though individuals can
forage in more wider ranges, though the success of this shift in tactics is debatable. Another big
choice that an adult must make is their prey type. Do they focus on the size of their prey or their
high/low lipid content? Not every pair forage the same as earlier mentioned but colonies can
easily have a wide range of prey counts in comparison. Yearly shifts in prey types tends to
represent some shift in traditional forage locations or newer breeding adults seeking to establish
new forage sites.
Table 1 Wet mass energy density values of four common prey types for Pigeon Guillemot in the
Puget Sound. Based on Table 1 from Litzow et. al., (2002)

Prey Type
Pacific Sand Land
Prickleback
Gunnel
Sculpin

Scientific Name
Ammodytes hexapterus
Lumpenus spp.
Pholidae
Cottidae

kJ g-1
5.25
4.76
4.69
4.10

The study of fluctuating abundance counts and unexpected collapse in marine birds is a
well-documented phenomenon (Stier et. al., 2020). The Pigeon Guillemot has been the subject of
research by several scientists since the 1950’s, primarily along the west coast with the focus on
the Gulf of Alaska (Litzow, Piatt, Abookire, Speckman, et. al., 2004) and the Farallon Islands in
California (Nelson, 1987). While much of this research was conducted outside of the Puget
Sound it is important to understand as the breeding habits, risks to Pigeon Guillemot, and results
of prior studies. This thesis follows in the footsteps of those studies by examining the possible
influence of prey types on the abundance of breeding colonies of Pigeon Guillemot in the Puget
Sound.

5

Natural History of Pigeon Guillemot
The Pigeon Guillemot is a small pigeon-sized seabird that is a member of the Auk family,
the Alcidae. They are a monomorphic species; both male, and female adults have entirely black
feathers with white wing patches. They also have bright red feet and gape (Drent, 1965).
Nonbreeding juveniles have smudgy black and white bodies. They reach sexual maturity at 3-5
years, with an average lifespan of 6- 8 years, although the oldest recorded Pigeon Guillemot was
15 years old (Cornell Lab of Ornithology, n.d). They generally mate for life with the male
returning to the same colony earlier than its mate to claim a burrow. The females will arrive a
week or two later than the male to join their partner in courtship displays. Their courtship
displays consist of circling and bill-touching. Rapid zigzag chases on water near the colony have
also been observed (Kenn Kaufman, 2019). The male and female share incubation and feeding
tasks to ensure their brood is successful. Pigeon Guillemot colonies tend to be centered around
cliffside burrows along the coast though some cases of utilizing downed logs, piers, and other
structures have been recorded (Bishop et. al., 2016). In North America, the Pigeon Guillemot has
a range along the coastal waters from southern California to Alaska (Ewins, P.J, 2020).
The Pigeon Guillemot native to the Puget Sound winter in the northern Salish Sea, they
return to their original colonies during breeding season, from April to September, to attempt to
mate. Upwards of 40% of the colony are generally comprised of non-breeding juveniles who
have been unsuccessful in acquiring a mate and/or a burrow (Harkness, 2017). The feeding
habits of different Pigeon Guillemot colonies can prove to be interesting as some will forage in
the same location year after year and others will be broader in their feeding habits. Their
dependence on specific benthic fish also reveals otherwise hard to observe shifts in those fish
stocks as the Pigeon Guillemot abundance shifts are largely dependent upon prey availability

6

(Litzow, Piatt, Abookire, & Robards, 2004b), though there are various factors that can impact
this abundance in outlier events, such as high-water temperatures and pollution in the water.
They also have a relatively large and stable abundance counts which allows dips and variances to
be more observable.
Threats to Pigeon Guillemot abundance
Pigeon Guillemots like many marine birds are notoriously susceptible to pollutants. The
Pigeon Guillemot is the only marine bird species that is “considered as not recovering from the
1989 Exxon Valdez oil spill (Bixler, 2010). The impacts on Pigeon Guillemot in Alaska could
easily be seen in the Puget Sound if it were to suffer a similar environmental pollution event or
seen on a smaller scale by localized pollution events. The impacts of pollution can be directly
connected to the Pigeon Guillemot as they suffer die-off or indirectly through their prey, forcing
shifts from their traditional foraging habits to new, less beneficial foraging sites.
Rising sea levels have two large impacts upon Pigeon Guillemot as a species (Vermeer
et. al., 1993). Firstly, Pigeon Guillemot have greater foraging success in lower tides as it
provides easier access to their prey and a rising sea level will make their catch success decrease
which will mean increased risk of predation as they are forces to make further attempts and a
decrease in the success of their chicks to fledge. Adults might be forced to pick less nutritional
prey to feed their chicks or decrease their brood numbers which would have far reaching impacts
on their abundance over an extended period. As a coastal burrow nesting species rising sea levels
can increase the risk of erosion to their traditional nesting sites, forcing them to decrease their
breeding pairs, relocate or lose entire colonies. While there is a natural shift of colonies over long
periods of time due to natural erosion a much faster rate of erosion could force such transitions to
new colony sites more often, much more than Pigeon Guillemot are adapted to. Colony
7

attendance by Pigeon Guillemot is widely dependent on tidal heights. Tidal height impacts
foraging behavior and food availability, which in of itself also influences the colony attendance
as many birds are absent due to foraging (Vermeer et. al., 1993). Pigeon Guillemot are generally
classified as mid-water foragers, meaning that the tide flow did not really cause too much impact
on their foraging habitat and those in the mid-range tend to have the most diverse level of
foraging strategies (Drew et. al., 2013).
Pigeon Guillemot are threatened by increasing water temperatures both directly and
indirectly. Indirectly the impacts on their forage fish while varied by species could still cause
some disturbance to those Pigeon Guillemot who focus on specific fish more so than those
Pigeon Guillemot who have a wide-ranging foraging style. An increased difficulty in feeding and
unseasonal shifts in water temperatures, even the lack of upwelling winds to increasing nutrient
availability has been shown to reduce reproduction success as was seen in the Farallon Islands in
the mid-1800s which could easily occur in other temperature dependent locations (Lewis, 1974).
Prey base
While Pigeon Guillemot are known to eat a wide variety of prey throughout their large
range the focus on Puget Sound means that the prey types discussed will focus on that region.
The majority of foraging conducted by Pigeon Guillemot during the breeding season is within
0.2 – 7.0 km from the colony (Vermeer et. al., 1993b), and like many marine birds are centralplace foragers during their breeding season (Bolton et. al., 2019), the precise relationship on their
colony density will be dependent upon surrounding coastal morphology, which is varied within
both regions.
The two main prey types for nesting Pigeon Guillemot in Puget Sound are the Sculpin
(Cottoidea) and Gunnel (Pholis laeta) (Lee & Grant, 2018). Pigeon Guillemot are known to have
8

traditional forage sites where they routinely forage specific fish types. Declines in abundance of
Pigeon Guillemot in Alaska have been linked to the loss of forage food availability (Romano,
1997) as they were forced to switch from high-lipid to low-lipid prey. This study also showed
that those Pigeon Guillemot who switched to low lipid tended to have lower fledgling success of
their chicks. Another factor for chick fledgling success is those Pigeon Guillemot who specialize
in selecting prey items for their chicks than those members of their species who have more
generalized forage habits (Golet et. al., 2000). This same study pointed to the fact that the size of
prey from specialized hunters might have had far more importance than just the high lipid levels
of their prey. This also has the benefit of reducing the risk of predation on the chicks, as the
feeding trips are reduced. Specialization also did not affect chick growth in the early stages
which pointed to a focus on quality over quantity. Golet et. al., (2000) also points to the
importance not only of high-lipid prey but low-lipid prey, while high-lipid prey is important for
its nutritional impacts those prey types tend to have more movement through the environment
while low-lipid prey is more residential in their movements. So low lipid prey can sustain chicks
while the high lipid prey can produce increased growth rates. This is likely the reason Pigeon
Guillemot do not specialize in specific high-lipid prey to maintain a more generalized foraging
habit. Alongside the sculpin and gunnel Pigeon Guillemot are known to eat are recorded to eat a
handful of other prey types. Additional prey types for Pigeon Guillemot in the Puget Sound is
Pacific Cod (Gadus macrocephalus), Sand Lance (Ammodytes hexapterus), Surf Perch
(Embiotocidae), and Prickleback (Stichaeidae).
The Junk Food Hypothesis as explored by Österblom et. al. (2008), is the correlation of
predatory fish and mammals eating prey that is low lipid in comparison to their normal prey,
which lowers the weight gain of their own weight and most importantly, their chicks. Weight

9

gain is key to the survival of fledgling chicks and juveniles through their first few years.
Abundance declines can be seen to occur in correlation with shifts in prey types, for example in
sea lions (Österblom et. al., 2008). In the same regions where sea lions saw decline seabirds in
the same region also suffered abundance decline. In the research conducted by (Litzow et. al.,
2004), predators such as Pigeon Guillemot will trade off high lipid prey for a more consistent
abundance of prey, even if it has lower lipid amount.
Pigeon Guillemot abundance can be negatively impacted by a shift in their fish stocks,
which has been shown to vary with decadal-scale climate variability (Litzow et. al., 2002). The
energy demands of growing chicks is high enough that a shift to low-lipid prey where their
energy density is not able to maintain a functioning population. Pigeon Guillemot tend to focus
their foraging habits on specific areas, so knowledge of their available fish types is possible.
Pigeon Guillemot must navigate the choice between quantity over quality with regards to
their fish type and the energy pay-off. This quality-variability trade-off hypothesis seeks to make
a connection between energy density and spatial-temporal variability in the abundance of prey,
primarily nearshore fish; with some findings that the Pigeon Guillemot is negatively affected by
shifts in the abundance of this prey (Litzow, Piatt, Abookire, Speckman, et. al., 2004). The
Pigeon Guillemot in the Puget Sound have a variety of prey to choose from.
Breeding Biology
Unlike most other species of the Auk family species Pigeon Guillemot lay two eggs per
clutch. As stated by Emms & Verbeek (1991) this is most likely due to their tendency to feed
closer on inshore benthic fishes while the other Alcidae tend to forage on offshore pelagic prey.
This reduces the amount of food they can bring to their young. At the same time, inexperienced
mating pairs often will lay a single egg per clutch, which can consist of 5-28% of mated pairs
10

(Emms et. al., 1991). The breeding season is often split by two clutches per season with the
second clutch often being a single egg. It has also been noted that food provisioning rates on
chicks is dependent on the chicks’ age, paying attention to the deliver rates (number of fish per
unit time) and estimating provisioning rates (biomass or energy per unit time (Emms & Verbeek,
1991). Besides factors such as chick age, tidal height, and time of day, the growth rate of the
chick can influence provisioning rates. The energy requirements of chicks slow as their growth
rate slows. Pigeon Guillemot are unlike other alcids in that their chicks are fast growing and the
reduction in provisioning may be due to encouraging their chicks to fledge (Golet, 2000).
Foraging is a high energy cost event with risk of predation so reducing delivery rates is
beneficial to the parents. By reducing delivery rates later in the season, the loss to the chicks is
minimized. Feeding rates are increased in the morning and evening hours while the colony
members forage though high tides will decrease the forage rate. Breeding pairs with a clutch of
two eggs will forage at an increase amount. Observed variation among nests in the proportions of
different fish types suggest either that individual birds specialize on different prey types or that
they foraged in areas that differ in relative abundance of prey types.

11

Chapter Three: Methods
Citizen Science Organizations
The organizations involved in the Pigeon Guillemot Group are varied in their reach,
scope, and goals. They have coordinated together to ensure the passing of information and a
uniform way in conducting their surveys. Among the primary organizations involved are
Audubon Societies around the Puget Sound; Olympic Peninsula, Vashon-Maury Island,
Dungeness River, Kitsap, Washington. The two primary regions this thesis focus on are the
Whidbey Island Audubon Society and the Nisqually Reach Nature Center which survey
Whidbey Island and the South Sound respectfully. The focus has been on the two organizations
due to their long time conducting this survey and are the two primary groups coordinating the
format of the survey.
Whidbey Island Audubon Society originally started the survey of the Pigeon Guillemot
throughout Whidbey Island. Whidbey Island initiated the surveys in 2002 and since that time
have taken a leadership role with the various other organizations as they got involved. The
second organization to join in 2011 was the Nisqually Reach Nature Center which coordinated
the South Sound survey volunteers. In 2020, the Washington State Department of Fish and
Wildlife took over the data storage for the organizations involved and has begun to utilize
Geographic Information Systems (GIS) programs to make an interactive survey for the
volunteers.

12

Whidbey Island
Survey begins

WFDW joins project
as GIS and Data
support

2002

2021

2013

South
Sound
Survey
begins
Figure 1: Timeline of organizations joining surveying of Pigeon Guillemot in the Puget Sound.

13

Figure 2: A typical breeding season survey for Pigeon Guillemot. The top section focuses on
abundance while the bottom (“Burrow Activity”) section focuses on prey county.

14

Region Descriptions
The sites in this study are split into two regions, South Sound and Whidbey Island, with
each further broken down into colonies. With 13 in South Sound (see Fig. 3) and 23 in Whidbey
Island (see Fig. 4 & 5), this study included data from 36 colonies. Those colonies that are close
to one another, sharing similar names are combined (e.g., Edgewater A, Edgewater B, Edgewater
C were combined into “Edgewater”). This is done as many of the colonies have young adults
who move about between related colonies (Mills et. al., 2014). Colonies are generally located
along coastal cliffs in both regions, while individual burrows can be found in sand, gravel, or
soil. Many of such burrows are small cavity in the soil type allowing the Pigeon Guillemot to
decrease predation by aerial predators, though the difficulty to reach some burrows can also
decrease mammalian predation, such as from raccoons. Some individual burrows can be small
crevices, gaps in man-made structures such as pier supports, or rock piles near the other burrows
of their colony. The size of each colony can vary greatly as their number of burrows and overall
abundance are not uniform. South Sound colonies which are spread along the various peninsulas
and islands centered on the Nisqually Reach Nature Center. South Sound colonies have much
smaller abundance counts than those in Whidbey Island.

15

Figure 3: The colonies of South Sound

16

Figure 4: The northern colonies of Whidbey Island

17

Figure 5: The southern colonies of Whidbey Island

18

Abundance Counts
As an annual estimate of abundance from each colony, the maximum count records each
year was used (abundance data from 2015 to 2020). Any colony that was missing 3 or more
years of abundance counts from 2015 to 2020 was not used in the analysis.
Prey Counts
The surveys utilized four main submissions for prey type brought to chicks. Surveyors do
this through visual identification of the fish catch, which is not as difficult as it could be due to
the Pigeon Guillemots’ habit of “dipping” (where the bird dips their fish repeatedly into the
water after catching it). The data for the prey types are sculpin, gunnel, and other/unknown
(Figure 2). Those fish types were selected as they are the primary forage for the Puget Sound
Pigeon Guillemot populations (Lee et. al., 2018).
Data Analysis
Data from the Whidbey Island and South Sound regions were analyzed separately,
without examining any direct connection between the two. Some analyses were based on
regional data (i.e. data summarized from colonies from either Whidbey Island or South Sound)
and others were based on colony-level data within each region. Statistical analyses were
performed in R version 4.0.4 (R Core Team, 2021), using packages as specified below.
Regional analysis
Linear regression was used to determine whether abundance counts, specifically the sum
of colony abundance within a region, a significant positive or negative trend from 2015-2020.
Similarly, the sum of all prey count observations were analyzed using a χ2 test of association to
ask whether the counts of different prey types were proportionally similar throughout the years.

19

Colony-Level Analyses
Within each region, linear regression was used to determine whether colony abundance
had a significant positive or negative trend from 2015-2020. Prey counts from one year (total,
gunnel, and sculpin) were correlated with the abundance of the colony in the following year
(e.g., prey counts from 2015 with the abundance of 2015), using Kendall’s Tau in the R package
“Kendall” (Mcleod, 2011). This analysis used data from 2014-2019 for prey types, and 20152020 for abundance.
A synchrony analysis was used to ask whether colony abundance, within each region,
varied synchronously or asynchronously. The R package “synchrony” (Gouhier, 2014) calculated
mean Pearson’s, Kendall’s W, and Spearman’s ranked correlation of colony abundance.

20

Chapter Four: Results
Abundance Counts
The overall Pigeon Guillemot abundance of the Whidbey Island and South Sound
colonies varied somewhat from year to year (Figure 5). South Sound abundance did not show
any significant trend over time (p = 0.22, adj. R² = 0.18). Whidbey Island abundance showed a
significant linear increase over time (p = 0.039, adj. R² = 0.62).

Significant linear increase

over time (p

(p

0.22, ad R²

0.0 9, ad R²

0.62)

0.1 )

Figure 5: South Sound and Whidbey Island annual abundance. The 5-year total is the sum of the
counts in each region for the 5-years (2015-2020) used in this study.

Prey Counts
In South Sound Pigeon Guillemot gunnel were observed more often compared to any
other prey, 69% across all the years (Figure 6; see Appendix 1 for counts by year). The
proportion of different prey types observed over varied over the years (χ²10 = 49, p < 0.001). For

21

example, 2018 showed a larger count of gunnel than one would expect by chance, based on
examinations of the χ² residuals.
In Whidbey Island Pigeon Guillemot gunnel were observed more often compared to any
other prey, 50% of their total prey being gunnel (Figure 7; see Appendix 2 for counts by year).
The proportion of different prey types observed varied over the years χ²10 = 144, p <0.001).
S O UT H S O UND TO TAL PRE Y CO UNT S
ꭓ²10 = 49, p < 0.001

Sculpin

Gunnel

Other

69% Gunnel

13

16

9

20

106

96

46

24

30

2018

2019

2020

168
10

33

78

72

58

25

18

19

2015

2016

2017

Figure 6: South Sound total prey counts. See appendix 1 for yearly prey diversity breakdowns.
69% of all prey was gunnel. χ²10 = 49, p < 0.001 showed the prey type varied significantly from
year to year.

22

WHIDBEY ISLAND TOTAL PREY COUNTS
Sculpin

ꭓ²10 = 144, p <0.001

Gunnel

Other

50% Gunnel
97

69

112
77

121

21
303

242

235

262

196

289

118

99

2015

2016

183

175

176

2017

2018

2019

228

2020

Figure 7: Whidbey Island total prey counts. See appendix 2 for yearly prey diversity
breakdowns. 50% of all prey was gunnel. χ²10 = 144, p <0.001 showed the prey type varied
significantly from year to year.
In the South Sound region, there was only one weak correlation between abundance and
prey types (Table 2). This correlation was for the Young’s Cove abundance counts weak
correlation with total prey (0.06).
Table 2: South Sound Colony Results. The regression coefficient column is from simple linear
regression of colony abundance with you (2015-2020. Correlation columns show Kendall’s Tau
of colony abundance with prey counts (Total, Sculpin, and Gunnel) from the previous year
(2014-2019). Significant correlations are marked in bold with *. In correlation results, n/a
represents missing prey count data.
Colony
Andy's Marine Park
Beachcrest
Big Fish Trap
Burfoot Park
Butterball Cove
Flapjack
Higgins Cove
Ketron South
Lyle Point

Regression
Coefficient
4.55
5.22
-0.22
0.17
3.85
-0.65
-1.14
-4.28
13.08

Correlation
w/total prey
n/a
0.66
0.75
-0.3
0.4
n/a
0.46
0.1
0.35

Correlation
w/sculpin
n/a
0.5
0.75
-0.3
0.31
n/a
0.56
0.35
0.64

Correlation
w/gunnel
n/a
0.66
0.75
-0.64
-0.2
n/a
0.46
-0.1
0.41
23

Mill Bight
Walnut Road
Young's Cove
Zangle Cove

-2.51
3.71
2.91
0.77

0.35
0.13
0.06*
-0.13

0.64
0.59
0.54
0.14

0.41
0.13
-0.57
-0.21

In the Whidbey Island region, there were several colonies that showed positive or
negative correlations between abundance and prey types (total prey, sculpin, and gunnel, Table
3). All of the correlations were weak (between -0.10 and 0.10). Cliffside abundance was weakly
correlated with the previous year’s total prey (-0.07), sculpin (0.08), and gunnel (-0.07). Double
Bluff abundance was weakly correlated with previous year’s total prey (-0.07) and sculpin (0.08). Malmo Bluff had one positive correlation with gunnel (0.06). Finally Mutiny Sands also
had a positive correlation with total prey (0.06).
Table 3: Whidbey Island Colony Results. Linear Trend represents simple linear regression of
colony abundance from 2015 to 2020. Kendall’s Tau correlation of colony abundance with prey
counts (total, sculpin, and gunnel) from the previous year, 2014 to 2019. Those results with
significance are marked in bold with *. Those results in bold show a correlation.
Colony

Regression
Coefficient

Correlation
w/total prey

Correlation
w/sculpin

Correlation
w/gunnel

Bush Point Dock

0.48

0

0.40

0

Cliffside

1.22

-0.07*

0.08*

-0.07*

-0.30

0.18

0.51

-0.40

Coupeville Wharf

1.34

-0.33

0

0

Double Bluff

5.25

-0.07*

-0.08*

-0.23

Forbes Point

-0.9

0.20

-0.52

0.10

Fort Casey North

5.54

0.41

0.55

-0.13

-0.08*

-0.33

0.43

-0.20

Hastie Lake South

-0.17

0.20

0.33

-0.20

Keystone

-3.79

0

-0.10

-0.40

Lagoon North

-8.48

0.41

-0.27

0.73

Clinton Ferry Dock

Harrington

24

Regression
Coefficient

Correlation
w/total prey

Correlation
w/sculpin

Correlation
w/gunnel

8.94

0.33

0.66

0.66

-2

0.54

0.40

0.67

-1.22

0.00

0.69

0.06*

Monroe Landing

2.94

0.20

0.20

0.10

Mutiny Sands

3.48

0.06*

0.69

-0.46

Possession Point

-1.28

0.33

-0.14

0.13

Pratts Bluff

-0.80

0.27

0.21

0.35

Rolling Hills

-0.62

0.13

0.13

0.00

1.05

0.20

-0.13

0.69

Colony
Lake Hancock
Langley Marina
Malmo Bluff

Shore Meadows

Synchrony Analysis
Neither region demonstrated synchronous changes across the colony abundance counts
(Table 4). Using the mean Pearson correlation, Kendall’s W, or Spearman’s ranked correlation
did not influence the finding. In South Sound there was no correlation between the abundance
counts of the colonies suggesting those abundance counts are not influenced by one another
(Figure 5). For Whidbey Island there was no correlation between the abundance counts of the
colonies suggesting those abundance counts are not influenced by one another (Figure 6). It is
interesting that the abundance of Pigeon Guillemot is asynchronous as this has been found to
increase the risk in predation of marine birds, such as the Common Tern (Hernandez-Matias et.
al., 2003), but predation does not seem to be a large factor in Pigeon Guillemot abundance
counts in the Puget Sound.
Table 4: Synchrony Analysis of Pigeon Guillemot abundance from each colony per region. There
are no statistically significant results.

Mean Pearson Correlation

South Sound
-0.03

Whidbey Island
0.05
25

Mean Correlation p-value (two-tailed test)
Kendalls W (uncorrected for tries)
Kendall’s W (corrected for tries)

0.54
0.07
0.07

0.12
0.04
0.04

Kendall’s W p-value (one-tailed test)
Spearman’s ranked correlation

0.40
0.00

0.39
0.00

Chapter Five: Discussion
The study of fluctuating abundance counts, and unexpected collapse is a welldocumented phenomenon in herring, though this can be possible in many organisms (Stier et. al.,
2020). Population dynamics are an important factor to understand when it comes to species in
the Puget Sound. To project those counts into the future, we can generate expected abundance in
a generation as a direct function of individuals in a previous generation (Heino et. al., 1997). By
knowing the population of the Pigeon Guillemot, we can tie it in with both wildlife conservation
and economy focused endeavors (Cusack et. al., 2019) as the utilization of statistical analyzes to
produce timely adaptive management plans.
Differences in overall abundances from Whidbey Island and the South Sound is a
complicated subject. There are many factors which could influence their large difference, South
Sound has colony abundance in the tens, Whidbey Island often will go up to the hundreds.
Papers such as (Heino et. al., 1997) show that subpopulations of a species can be negatively
impacted by traveling long distance, so the fact the Pigeon Guillemot populations in Puget Sound
stay year-round, rather than migrate any great distance, this would suggest that the population
should be stable, lending more credence to their prey being a much bigger factor to their
abundance counts. So future studies into their primary prey (gunnel and sculpin) is important.
Other factors that could influence this wide range of colony abundance including traditional sites
survival (i.e., natural, and man-made erosion and human interference be it through producing

26

loud noises which Heino (1997) mentioned as a negative factor to a species population or
disturbing them directly at their colonies. Other environmental factors no doubt influence the
abundance counts of each region and colony individually, as earlier shown (Figures 3, 4, and 5)
the colonies of each region are widely dispersed. One major factor for the much larger
abundance counts of Whidbey Island is likely due to the island’s location closer to the wintering
grounds and more foraging opportunities. Perhaps there is a large gunnel population in the area,
or their hunting is easier, leading to a greater success rate and the slight increasing trend. The
variety of abundance counts of the two regions points to the asynchrony of colony abundances,
which is surprising given the colonies’ proximity to one another. It is worth nothing that
population synchrony could be operating, and potentially detected with many more years of data,
but that is beyond the scope of this thesis. In a future study it might be interesting to see if there
is any synchrony with abundance counts in a colony in a single year, to see if they perform in
similar ways to other seabirds, like the glaucous-winged gull (Larus glaucescens) which lay their
eggs in synchrony with one another in their colonies (Henson et. al., 2011). An example of
abundance synchrony is the study of several grazing birds (Greenland, Svalbard barnacle geese,
Greenland white-fronted goose, Greylag goose, and Svalbard pink-footed goose, along with the
common crane) in northern Europe which showed variable synchrony in both the short- and
long-term abundance counts (Cusack et. al., 2019). This variation was due to differing
management goals, and lack of consistent monitoring; all factors which could play a role in
Pigeon Guillemot synchrony.
While the proportions of each prey type recorded varied from year to year, gunnel was
observed the most often in both regions. Though the amounts taken did vary throughout the years
as shown by the ꭓ²10 results. This is not totally unexpected as the data was for only six years and

27

not all the colonies had enough data to analyze, decreasing the pool of data for the study. There
are of course many possible reasons for the higher counts of gunnel. As mentioned by Lee
(2014) in their surveys they noted a much larger amount of gunnel than sculpin, about three
times as much. One suggested reason for this tendency to feed on gunnel is due to the bony
nature of sculpin which can make failures more often as digestion is more difficult. It is worth
noting here that sculpin only contain 7% of the gunnel’s total wet energy mass, which could be
another key factor in the foraging of more gunnel than sculpin (Table 1). It is worth gunnel is not
the most nutritional prey types available to Pigeon Guillemot which might reinforce the idea that
breeding pairs forage specific sites, more study into this is needed.
Nelson (1987) focused on the importance in trying to connect prey and abundance data
together while also collecting quantitative data for the attendance of colonies. This was the main
motivation for me to examine the data on individual colony abundance and prey counts,
potentially to test the junk-food hypothesis. It is interesting that in table 1 there is evidence to
show other more energy efficient prey types that Pigeon Guillemot could forage on, but they tend
to take gunnel and sculpin, with gunnel being the top prey item for both regions. Their energy
needs are presumably influenced by distance, forage habits of the colony, and their needs to
fledge their chicks. Pigeon Guillemot are known to feed their chicks varied amounts of prey
throughout their growth to pack on weight and encourage chicks to fledge. We do not actually
know what the adult Pigeon Guillemot are eating themselves, though high-lipid prey would
increase their reproductive performance (Golet, 2000). As they might be feeding themselves a
larger variety of prey in comparison to their chicks. They may seek quantity over quality to bulk
up their chicks. Golet also found that Pigeon Guillemot who specialized in prey items had a
higher reproductive success that those who were more generalized in their approach (2000). To

28

successfully forage like any organism Pigeon Guillemot, need to assess prey distribution and
abundance as the energy costs of acquiring prey needs to be maintained at a viable level (Dall &
Cuthill, 1997), and by specializing in a specific fishing site(s) they reduce much of the energy
costs.
For the future it is important to see how the format of the survey can be improved upon or
add additional information to be utilized by the various organizations that are working with the
Pigeon Guillemot Group. To gain a better understanding of the pairing of Pigeon Guillemot
mating pairs and their utilization of a specific burrow could be made easier to identify through
banding. This banding process have been conducted successfully in the past by researchers on
the South Farallon Islands (Tenaza, 1966). The format utilized in that study of banding allowed
Tenaza to not only confirm that the mated pairs returned the following year but returned to their
prior nesting burrow (1966). By having such a process completed in the past reinforces the fact it
could possibly be done on a larger scale in the Puget Sound.
The survey currently does not specify which burrow was being utilized by the mating
pairs, a marking system could be devised such as painting rocks and wood near the burrows to
improve identification to allow surveyors to mark them down on the surveys. Such a marking
system would also assist in more in-depth scientific research on specific mating pairs, their
eggs/chicks, and reproduction success. An additional way to mark sites would be by utilizing
GIS to mark the colonies on digitally formatted pictures of the colonies. An established layout of
the burrows would help reduce misinformation.
As the organizations involved in the Pigeon Guillemot Program increase their expertise
will continue to help the organization and its success grow. Data collected could help reveal
more in-depth knowledge of Pigeon Guillemot abundance, colony shifts, die-offs, and the like.
29

While the diet of the Pigeon Guillemot is key to their chick’s survival and the return rates
for following years, this project did not demonstrate clear evidence of correlation between prey
counts the previous year and colony abundance. A handful of sites, primarily in Whidbey Island,
had statistically significant correlations but these were both positive and negative, and always
weak (between -0.10 and 0.10). There are some colonies which show near significance between
0.05 and 0.010, so this supports more in-depth study with larger data sets to be conducted in the
future. The fact that the Whidbey Island abundance counts positive linear trend points towards
some statistical significance is a sign that the data is important. Each region was analyzed
independently of one another due to their varied abundance counts and regions distance, and the
results shows how differently the two regions are. The idea of Pigeon Guillemot as a marine
indicator is still a conversation to have, though Whidbey Island does seem to have enough data
to support its use as information used in conservation and management.
Gunnel is obviously an important prey source for breeding Pigeon Guillemots in the
Puget Sound, and future study into their relationship could prove rather important to the overall
success of both species (Figure 6,7, Appendix 1, 2). Understanding the reasons for this finding is
important for the future management of the Pigeon Guillemot. Combined with the lack of
correlation with prey types this may support the findings that Pigeon Guillemot forages for their
prey within 4 miles from their colony (Litzow, 2000). While there are many suggestions to why
their mostly observed feeding their chicks gunnel, this study cannot confirm any of those
hypotheses. There is a lack of data specifically on gunnel and sculpin in Puget Sound which
makes determination of their influence on Pigeon Guillemot feeding habits impossible currently.
A study in the future to test if Pigeon Guillemot prefer gunnel would be an interest addition to
the research done on the Pigeon Guillemot.

30

Bibliography

A.I. McLeod (2011). Kendall: Kendall rank correlation and Mann-Kendall trend test. R package
version 2.2. https://CRAN.R-project.org/package=Kendall
Bishop, E., Rosling, G., Kind, P., & Wood, F. (2016). Pigeon Guillemots on Whidbey Island,
Washington: A Six-Year Monitoring Study. Northwestern Naturalist, 97(3), 237–245.
https://doi.org/10.1898/nwn15-31.1
Bixler, K. S. (2010). Why Aren’t Pigeon Guillemots in Prince William Sound, Alaska Recovering
from the Exxon Valdez Oil Spill? [Oregon State University].
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rb68xg25k
Bolton, M., Conolly, G., Carroll, M., Wakefield, E. D., & Caldow, R. (2019). A review of the
occurrence of inter-colony segregation of seabird foraging areas and the implications for
marine environmental impact assessment. Ibis, 161(2), 241–259. Blackwell Publishing Ltd.
https://doi.org/10.1111/ibi.12677
Bull, J. W., Gordon, A., Law, E. A., Suttle, K. B., & Milner-Gulland, E. J. (2014). Society for
Conservation Biology Importance of Baseline Specification in Evaluating Conservation
Interventions and Achieving No Net Loss of Biodiversity. Biology, 28(3), 799–809.
https://doi.org/10.1111/cobi
Cairns, D. (1979). Censusing Hole-Nesting Auks by Visual Counts. Bird-Banding, 50(4), 358364. https://doi.org/10.2307/4512487

31

Cornell Lab of Ornithology (n.d). Pigeon Guillemot Overview, All About Birds, Cornell Lab of
Ornithology. Overview, All About Birds, Cornell Lab of Ornithology.
https://www.allaboutbirds.org/guide/Pigeon_Guillemot/overview.

Cusack, J. J., Duthie, A. B., Rakotonarivo, O. S., Pozo, R. A., Mason, T. H. E., Månsson, J.,
Nilsson, L., Tombre, I. M., Eythórsson, E., Madsen, J., Tulloch, A., Hearn, R. D., Redpath,
S., & Bunnefeld, N. (2019). Time series analysis reveals synchrony and asynchrony
between conflict management effort and increasing large grazing bird populations in
northern Europe. Conservation Letters, 12(1). 10-11. https://doi.org/10.1111/conl.12450
Dall S. R. X., and I. C. Cuthill. 1997. The information costs of generalism.
Oikos 80:197–202.

Department of Fish and Wildlife. (1970, April 06). Washington Department of Fish & Wildlife.
Retrieved February 09, 2021, from https://wdfw.wa.gov/

Drent, R. H. (1965). Breeding biology of the Pigeon Guillemot, Cepphus Columba. Ardea, 53(34). University of British Columbia.Thesis.
Drew, G. S., Piatt, J. F., & Hill, D. F. (2013). Effects of currents and tides on fine-scale use of
marine bird habitats in a Southeast Alaska hotspot. Marine Ecology Progress, 487, 275–
286. https://doi.org/10.2307/24892125
Emms, S. K., & Verbeek, N. A. M. (1991). Brood Size, Food Provisioning and Chick Growth in
the Pigeon. The Condor, 93(4), 943-951. https://www.jstor.org/stable/3247729

32

Ewins, P. J. (2020). Pigeon Guillemot (Cepphus columba), version 1.0. In Birds of the World (A.
F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
https://doi.org/10.2173/bow.piggui.01
Gaydos, J. K., & Pearson, S. F. (2011). Birds and mammals that depend on the Salish Sea: A
compilation. Northwestern Naturalist, 92(2), 79-92. https://www.jstor.org/stable/41300886
Golet, G. H., Kuletz, K. J., Roby, D. D., & Irons, D. B. (2000). Adult prey choice affects chick
growth and reproductive success in Pigeon Guillemot. The Auk, 117(1), 82-91.
https://academic.oup.com/auk/article-abstract/117/1/82/5561605
Harkness, B. (2017). An assessment of population genetic structure in Guillemots (Cepphus).
http://hdl.handle.net/1974/23632

Henson, S. M., Cushing, J. M., & Hayward, J. L. (2011). Socially induced ovulation synchrony
and its effect on seabird population dynamics. Journal of Biological Dynamics, 5(5), 495516. doi:10.1080/17513758.2010.529168

Hernández-Matías, A., Jover, L., & Ruiz, X. (2003). Predation on common Tern eggs in relation
to sub-colony Size, Nest aggregation and Breeding Synchrony. Waterbirds, 26(3), 280-289

Kenn Kaufman. (2019). Pigeon Guillemot Cepphus columba. https://www.audubon.org/fieldguide/bird/pigeon-guillemot
Lee, T., & Grant, J. (2018). South Puget Sound and Nisqually Reach Aquatic Reserve Pigeon
Guillemot Breeding Surveys 2016-2018 Monitoring Report Prepared for: Nisqually Reach
Aquatic Reserve Citizen Stewardship Committee. https://www.aquaticreserves.org/,
Lewis, D. G. A. and T. J. (1974). The History of Farallon Island Marine Bird Populations , 185433

1972 The Condor, 76(4), 432–446.
Litzow, M. A., Piatt, J. F., Abookire, A. A., & Robards, M. D. (2004). Energy density and
variability in abundance of pigeon guillemot prey: Support for the quality-variability tradeoff hypothesis. Journal of Animal Ecology, 73(6), 1149–1156.
https://doi.org/10.1111/j.0021-8790.2004.00890.x
Litzow, M. A., Piatt, J. F., Abookire, A. A., Speckman, S. G., Arimitsu, M. L., & Figurski, J. D.
(2004). Spatiotemporal predictability of schooling and nonschooling prey of Pigeon
Guillemots. Condor, 106(2), 410–415. https://doi.org/10.1650/7330
Litzow, M. A., Piatt, J. F., Prichard, A. K., & Roby, D. D. (2002). Response of pigeon guillemots
to variable abundance of high-lipid and low-lipid prey. Oecologia, 132(2), 286-295.

Mills, A., Lee, T., & Joyce, J. (2014). Pigeon Guillemot Foraging and Breeding Survey in and
Near the Nisqually Reach Aquatic Reserve 2014 Monitoring Report. Olympia, WA:
Nisqually Reach Aquatic Reserve Citizen Stewardship Committee.

Nelson, D. A. (1991). Demography of the Pigeon GUILLEMOT on southeast FARALLON
Island, California. The Condor, 93(3), 765-768. doi:10.2307/1368213

Nelson, D. A. (1987). Factors Influencing Colony Attendance by Pigeon Guillemots on
Southeast Farallon Island. The Condor, 89(2), 340-348.
Österblom, H., Olsson, O., Blenckner, T., & Furness, R. W. (2008). Junk-Food in Marine
Ecosystems. Oikos, 117(7), 967-977.
Piatt, J. F., Sydeman, W. J., & Wiese, F. (2007). Introduction: A modern role for seabirds as

34

indicators. Marine Ecology Progress Series, 352, 199–204.
https://doi.org/10.3354/meps07070
Romano, M. (1997). Effects of Diet on Growth and Development of Nestling Seabirds. January
1999, 1–39.Thesis.
Romano MD, Piatt JF, Roby DD (2006) Testing the junk-food hypothesis on marine birds:
effects of prey type on growth and development. Waterbirds 29:407–516
Stier, A. C., Olaf Shelton, A., Samhouri, J. F., Feist, B. E., & Levin, P. S. (2020). Fishing,
environment, and the erosion of a population portfolio. Ecosphere, 11(11).
https://doi.org/10.1002/ecs2.3283
Tenaza, R. (1966). Pigeon Guillemot Banding Returns. Bird-Banding, 37(4), 288-289.
Vermeer, K., Morgan, K. H., & Smith, G. E. J. (1993). Colony Attendance of Pigeon Guillemots
as Related to Tide Height and Time of Day. Colonial Waterbirds, 16(1), 1-8.
Vermeer, K., Morgan, K. H., & Smith, G. E. J. (1993b). Nesting Biology and Predation of
Pigeon Guillemots in the Queen Charlotte Islands, British. Waterbirds, 16(2), 119-127.

35

Appendix 1: South Sound Prey Count Dynamics
Appendix 1 contains a breakdown of prey count totals for South Sound by year showing
the overall diversity. Showing a large focus on gunnel by the colonies.

2015 South Sound Prey Count Diversity

Sculpin

Gunnel

Other

2016 South Sound Prey Count Diversity

Sculpin

Gunnel

Other

2017 South Sound Prey Count Diversity

Sculpin

Gunnel

Other

36

2018 South Sound Prey Count Diversity

Sculpin

Gunnel

Other

2019 South Sound Prey Count Diversity

Sculpin

Gunnel

Other

2020 South Sound Prey Count Diversity

Sculpin

Gunnel

Other

37

Appendix 2: Whidbey Island 2 Prey Count Dynamics
Appendix 2 contains a breakdown of prey count totals for Whidbey Island by year showing the
overall diversity. Showing a large focus on gunnel by the colonies.

2015 Whidbey Island Prey Count Diversity

Sculpin

Gunnel

Other

2016 Whidbey Island Prey Count Diversity

Sculpin

Gunnel

Other

2017 Whidbey Island Prey Count Diversity

Sculpin

Gunnel

Other

38

2018 Whidbey Island Prey count Diversity

Sculpin

Gunnel

Other

2019 Whidbey Island Prey Count Diversity

Sculpin

Gunnel

Other

2020 Whidbey Island Prey Count Diversity

Sculpin

Gunnel

Other

39