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thesis entitled

FEMALE SOCIALITY IN THE COMMON EIDER (Somateria
mollissima).

presented by

LAURA MCKINNON

has been accepted towards fulfillment
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FEMALE SOCIALITY IN THE COMMON EIDER (Somateria mollissima).
By

Laura McKinnon

A THESIS
Submitted to
Michigan State University
in partial fiilfillment of the requirement for the degree of
MASTER OF SCIENCE
DEPARTMENT OF ZOOLOGY

2005

ABSTRACT

FEMALE SOCIALITY IN THE COMMON EIDER (Somateria mollissima).

By

Laura McKinnon

The adaptiveness of social phenomena such as group living can be explained by the
concept of inclusive fitness when kin relationships exist between individuals within
groups. I investigated the presence of kin-based sociality among females in the common
eider (Somateria mollisima). Previous studies of female sociality in common eiders have
been restricted to observations during brood rearing. Here I provide a novel, empirical
framework using molecular markers and field sampling to genetically characterize female
social groups at several stages of the common cider life cycle. Throughout each of
several stages including in-flight colony arrival, nesting and brood rearing, I provide the
first genetically confirmed evidence of female kin-based social groups in common eiders
and Anseriformes in general. Further research directed at measuring fitness benefits of
sociality in common eiders and other Anseriformes could provide important insight into

the benefits and evolution of sociality in migratory avian species.

ACKNOWLEDGEMENTS

This completion of this thesis would not have been possible without the help of several
great fi‘iends and scientists. First of all I would like to acknowledge my primary advisor
Dr. Kim Scribner as well as Dr. Grant Gilchrist, for providing invaluable scientific
advice throughout the entire process of preparing my Masters’ thesis. Together they
have made the journey through this degree, both challenging and enjoyable. I would
like to specifically thank Dr. Scribner for accepting me into his laboratory, despite my
limited knowledge of molecular techniques. Likewise, I thank Dr. Gilchrist for
sparking my interest in arctic nesting seaducks, and encouraging me to take filII
advantage of his well established study site and methodologies for my thesis. I have
learned more than I ever thought possible both in the laboratory and in the field. I would
also like to thank my committee members, Dr. Catherine Lindell, Dr. Harold Prince and
Dr. Kay Holekamp for their expert advice throughout the writing of my proposal and the
final thesis. The individuals who inspired me to investigate social behaviors in female
common eiders, those being the other crazy graduate students at East Bay; Karel Allard,
Kerrith McKay and Peter and Mary Fast to name a few, are gratefully acknowledged.
Data collection for the 2003 season would not have been a success without Kerrith
McKay, Cindy Anderson, Joel Bety, Helen Jewell, Dave McCruer and Chantal Foumier
who risked cold arctic winds and polar bears to collect samples with me. These hard
earned samples would not have been analyzed without help from my colleauques in the
molecular ecology lab, specifically Scot Libants, Kristi Filcek, Laura Main (who taught

me how to use a pipette), Bronwyn Williams and Jeanette McGuire. Finally, this study

iii

would not have been possible without a valued teaching assistantship from the College
of Natural Sciences, Department of Zoology, and funds granted from the Dr. M.
Hensley Foundation and the Wallace Foundation. In addition, financial support was also
provided by the College of Agriculture, Department of Fisheries and Wildlife and the

field support by the Canadian Wildlife Service.

iv

TABLE OF CONTENTS

List of Tables ...................................................................................... vi
List of Figures ..................................................................................... vii
Introduction ......................................................................................... 1
Methods ............................................................................................. 7
Results ............................................................................................. 23
Discussion ......................................................................................... 33
Literature Cited ................................................................................. 44

LIST OF TABLES

Table 1: Modified PCR conditions .............................................................. 21

Table 2: Allelic Richness and Observed and Expected Heterozygosity for background
samples at 10 polymorphic loci .................................................................. 24

Table 3: Mean pair-wise relatedness values as calculated in Kinship 1.3.1 (Goodnight
and Queller 1999) for all groups and results of one-tailed permutation tests (Ratnayeke
et al. 2002) testing for differences between mean relatedness of females in groups versus
background levels. ............................................................................... 25

Table 4: Mean pair-wise relatedness values as calculated in Kinship 1.3.1 (Goodnight and

Queller 1999) for all groups and results of one-tailed permutation tests (Ratnayeke et al.
2002) testing for differences in mean relatedness within versus between groups. 27

Table 5: Group composition of amalgamated broods captured in walk in traps during
colony departure. ................................................................................ 32

vi

LIST OF FIGURES

Figure 1: General location of East Bay on Southampton Island, Nunavut, Canada (64°
02’ N, 81°47’W) ................................................................................... 8

Figure 2: Front view and profile of nylon salmon gill net suspended between 2 metal
poles used to capture common eiders in flight upon arrival to the colony. ............... 13

Figure 3: Walk-in wire nest trap used to capture females on the nest during incubation
(modified from Weller 1957). .................................................................... 17

Figure 4: Wire walk-in trap used to capture females and young departing the island in
groups. .............................................................................................. 18

Figure 5: Distribution of relatedness values A) between females within arriving groups,

B) between females and 3 nearest neighbors and C) between females in departing groups
set against background levels of relatedness for the colony. ............................... 28

vii

INTRODUCTION

Social behaviors such as group foraging, communal nesting and communal
rearing of young have typically been studied in terms of their positive effects on
reproductive success and survival (Hamilton 1964, Maynard-Smith and Price 1973,
Alexander 1974). Social environment is recognized as an important force in the
evolution of life history traits (Hoglund and Sheldon 1998, Svensson and Sheldon 1998).
General life history theory predicts that life history traits co-evolve as a consequence of
tradeoffs between age-specific reproductive success and survival (Steams 1976). Most
studies in life history theory have focused on a few key traits that affect reproductive
success, including number of mates, number of matings, clutch size and parental
investment (Steams 1976, Bateman 1948). Understanding how interactions between
individuals within groups can affect these life history traits is essential to understanding
the evolution and adaptive significance of group living.

Group living and social behaviors have evolved due to increased fitness accrued
to individuals living in groups (Alexander 1974, de Waal and Tyack 2003). Specific
benefits of sociality can include reduced predation pressure (Haas and Valenzuela 2002),
improved foraging efficiency (Whitehead 1996, Clutton-Brock et al.1999), defense of
resources, and improved care of offspring (Whitehead 1996, Silk et a1. 2003, Clutton-
Brock et a1. 2004). Costs associated with sociality include increased competition,
disease and exploitation of parental care (Alexander 1974, de Waal and Tyack 2003).

In order for group living to be adaptive, these benefits must outweigh the costs in terms

of fitness to individuals within the group. If kin relationships exist between individuals

within social groups, fitness benefits to social individuals can be increased via kin
selection. Kin selection (Queller 1992, Griffin and West 1992) incorporates the concept
of inclusive fitness (Hamilton 1964) to explain the adaptiveness of social behaviors. A
behavior that appears altruistic and even costly such as increased vigilance in groups,
may in fact be adaptive if fitness lost by the performance of the behavior (eg. less
energy allocated to reproduction) is compensated for by fitness gained through related
individuals as a result of this behavior.

Kin-based social groups have been described in many organisms in terms of both
duration and composition (reviewed in Griffin and West 2002). Temporary kin-based
social groups that typically form within a breeding season, such as parent offspring
groups, are commonly observed (Alerstam 1990, Ely 1993, Warren et al. 1993, Ashcroft
1976). For example, temporary kin-based social groups are formed in Bewick’s Swans
(Cygnus colombianus) where parents protect young from foraging competition, thus
increasing the survival of their offspring (Scott 1980). Kin-based social groups that
extend beyond a single breeding season are less common but are observed in
cooperatively breeding groups (Woolfenden 1976) and in matrilineal societies (Hawkins
and Klimstra 1970, Holekamp et a1. 1997). Males and females in cooperatively
breeding groups forego their own reproduction in order to help other related members
reproduce. Species such as meerkats (Suricatta suricatta) (Clutton-Brock et al. 2004),
scrub jays (Aphelocoma insularis) (Schoech et a1. 1996) and cichlid fish
(Neolamprologus pulcher) (Bergmuller and Taborsky 2005) increase their inclusive
fitness by providing extra vigilance or parental care for reproducing kin.

Among species where only. females provide parental care, extended kin-based

social groups are ofien based on female relationships. Kin groups based on female
relationships occur in several taxa, and may serve to lower predation risk of uni-parental
care while increasing access to resources for adults (Sterk et al. 1997, Munro and Bedard
1977b). For example, female sperm whales form ‘babysitting’ groups so that some
females can dive to optimal feeding areas without leaving their young unattended and
vulnerable to predation (Whitehead 1996). Female primates also form social
relationships with female kin, which decrease predation risk (Sterk et al 1997) and
increase reproductive success (Pope 2000). Among birds, social groups often form
during the brood rearing period to decrease predation risk and increase access to
resources for adults (Moreno et al. 1997, Lengye12002, Brown 1998, Cooper and Miller
1992, Cezilly et a1. 1994). In bird species exhibiting exclusive maternal care, these
groups are ofien composed of two or more adult females caring for young from several
different broods (Lengyel 2002, Munro & Bedard 1977aEadie et al. 1988, Ost et al.
2003). This behavior, referred to as brood amalgamation, is most prevalent in the
Anatidae, tribe Mergini (Bustnes et al. 2002, Eadie and Lyon 1998, Boos et al. 1989).
Fourteen of the 15 species in Mergini, amalgamate broods (Eadie et al. 1988). These
female social groups formed during brood amalgamation have been most extensively
studied in the common eider (Ost 1999, Ost et al. 2002, Ost et al. 2003). However kin
relationships within these social groups are still largely un-documented.

Despite the focus on female social groups during brood amalgamation, common
eider females may form kin-based social groups throughout several stages of their life
cycle, including migration and nesting. Theory and empirical data on the consequences

of behaviors suggest that group cohesion often has positive effects on fitness. Benefits of

group cohesion in common eiders during colony arrival may include energetic savings
during migration (Alerstam 1990), and the gathering of information on prime nesting
areas. Females may benefit by nesting in groups via increased vigilance against nest
predation and usurpation. Finally, females with young may benefit from departing with
other females and young via increased vigilance against predation and increased access
to resources for adults. The presence of female-based kin groups in common eiders may
indicate the potential for kin selection to influence fitness within these social groups.

Kin associations in other Anatidae have been inferred via behavioral
observations or observations of banded individuals (Regher et al. 2001 , Elder and Elder
1949, van de Jeugd et al. 2002). These relationships, however, have not been genetically
confirmed. The objective of this study is to identify genetically whether female kin-based
social groups exist in common eiders throughout several stages of their life cycle. By
providing evidence of kin groups in common eiders, we hope to show that female
sociality in Anatidae may not be restricted to the brood rearing period and that this
sociality may shape several life history characteristics shared by this group.

Our null hypothesis is that social groups in common cider females are random
with respect to relatedness. Our working hypothesis is that aggregations of female
common eiders that are commonly observed throughout the year are composed of related
individuals. Given that common eiders are philopatn'c to nesting areas, colonial, and
exhibit uniparental care, we predict that aggregations of adult females during migration,
nesting and brood amalgamation are related. Many Anseriformes are thought to migrate
from breeding areas to wintering areas in kin groups (Regher et al. 2001, Elder and Elder

1949), accordingly, we expect that kin groups will occur in common eiders during

migration. Specifically, we predict that estimates of mean coefficients of relatedness (a
surrogate measure of pedigree relationship) between females within groups arriving to
the colony will be greater than background levels of relatedness for the colony.
Anseriformes are also known to nest in kin groups (van de Jeugd et al. 2002). Thus we
expect that kin-based social groups will also exist during nesting. We predict that mean
coefficients of relatedness between females and nearest neighbors will be greater than
background levels of relatedness for the colony. Finally, because intense social
interactions between female common eiders leading to brood amalgamation occur in the
first few days following hatch (Ost and Kilpi 2000), we further predict that the
coefficients of relatedness between females within departing broods will be greater than
the background levels for the colony.

Here, we provide a novel, empirical framework using unique field methods and
molecular markers to sample random and focal females for a portion of the year when
females are on land and accessible to sampling. The migratory nature of birds ofien
limits our observations and conclusions about observed behaviors and their adaptive
significance. Seaducks and other Anseriformes are generally only accessible for study
during the breeding season. Most hypotheses regarding the importance of social
behavior in common eiders have been based only on the period when brood
amalgamation occurs. Observations and conclusions drawn from these studies are based
on activities at only one observational time point. The novelty of the approach taken here
is that we have expanded the time frame by designing a sampling strategy to access
information on female social groups at other times during their life cycle. We decompose

the sampling period into three specific phases that allow inferences to be made about a

portion of the yearly cycle during which the females are likely together but cannot be
sampled, such as on the wintering grounds. Finally we present empirical data for
relatedness between individuals in social groups and place these data in a more general
context in order to draw inferences about the evolution and significance of group living in

common eiders.

METHODS
Study location

Research was conducted at a common cider colony within the East Bay Migratory
Bird Sanctuary (East Bay) on Southampton Island, Nunavut, Canada (64° 02’ N,
81°47’W) (Figure 1). The common cider colony is located on a 26 hectare island
(Mitivik Island) within East Bay (Figure 1). The cider colony consists of up to 4000
breeding pairs annually. The island is characterized by tundra, low lying rocky outcrops
and several ephemeral fresh water ponds. One larger pond exists at the centre of the
colony and is a source of freshwater throughout the breeding season. Other nesting
species on the island include king eiders (Somateriafischeri), brant (Branta bernicla),
canada goose (Branta canadensis) and herring gulls (Larus argentatus). Predators of
common eiders eggs and ducklings include herring gulls (Larus argentatus), parasitic and
long-tailed jaegers (Stercorarius longicaudus ,and Stercorarius parasiticus respectively).
arctic foxes (Lepus arcticus) and less frequently, polar bears (Ursus maritimus). The
Canadian Wildlife Service (CWS) has been conducting a long-term study on the
reproductive ecology of the common cider colony at the site since 1996. Wooden study
blinds are situated throughout the colony and are accessed by above-ground canvas

tunnels to minimize disturbance to nesting common eiders.

Study Species
Common Eiders are a long-lived, itcroparous species with high adult survivorship
and delayed sexual maturity (Coulson 1984). Adults begin breeding after the 2nd or 3rd

year of age, breeding each year until 17 or 18 years of age (Baillie and Milne 1982,

 

 

 

 

 

 

 

Q
Legend
A -- Hudson Bay
8 - E at Bay Hum
Bid Seminary
C -- East Bay Elda' Colow

 

 

Figure 1. General location of East Bay on Southampton Island, Nunavut, Canada (64° 02’
N, 81°47’W).

Coulson 1984). Mating is seasonally monogamous (Goudic et al. 2000) and females are
highly philopatric to natal breeding colonies whereas males typically disperse (Anderson
et al. 1992, Cooch 1965, Wakeley and Mcndall 1976, Reed 1975). Migration to breeding
areas from wintering grounds occurs in large mixed-sex flocks. In combination with
longevity, female philopatry could encourage extended female kin associations during
migration and into the breeding season.

The nesting of common eiders can be considered both spatially aggregated and
temporally synchronous. Most female common eiders nest in colonies on small islands
(Goudic et a1. 2000), and lay eggs synchronously within days of each other. Nesting is
restricted within a short time period during the summer months (Cooch 1965) and laying
generally spans a period of 2-3 weeks (Gilchrist unpubl. data). During nest site selection,
females often spend several days prospecting for suitable nest cups throughout the colony
before selecting and laying in the final nest cup (Cooch 1965). Colonies are often
densely packed with available nest cups (150 nests/ha: Gilchrist unpubl. data), with many
nests reused in subsequent years. Nest site selection is partially driven by abiotic factors
such as cover from predators and protection from wind (Kilpi and Lindstrom 1997,
Cooch 1965). However, the close proximity of highly synchronous and philopatric
females could also be a factor in nest site selection. Close female kin associations could
be promoted throughout nesting and incubation if females select nest sites based on
proximity to relatives already nesting in the same natal nesting area. To summarize, the
potential for female kin associations among common eiders exists at several stages of the

life cycle, including migration, nesting and brood amalgamation.

Field Methods
Background levels of Female Relatedness in the Eider Colony

There are several methods of assessing levels of relatedness between individuals
within groups. Individuals can be grouped into categories of ‘pedigrec relationships’
based on coefficients of relatedness. Pair-wise coefficients of relatedness provide a
measure of relatedness between two individuals, and are estimated based on the
proportion of alleles shared between individuals adjusted based on population allele
frequencies (Goodnight and Queller 1999). Proportions of pedigree relationships
estimated within groups (i.c. close relatives (er > 0.5), other relatives (0.38>rx,<0. 12),
unrelated (rxy <0.12) can then be compared to the proportions estimated between groups
(Curry ct a1. 1988, Gompper et al. 1997). However, this method may misclassify
individuals into pedigree relationships. Depending on the genetic diversity of the
population being sampled, rxy values may not be indicative of the true pedigree. For
example, distantly related individuals in an inbred population will likely have a hi ghcr
r,y value than closely related individuals in a genetically diverse population.
Alternatively, estimates of mean relatedness between individuals within groups can be
compared to those between individuals between groups (‘outgroup’) within the same
population (Ratnayeke et al. 2002, Fuller et al. 2005). This method is superior to the
first method because a relative measure of relatedness is being compared within and
between groups. Finally, estimates of mean relatedness between individuals within
groups can be compared to the estimate of mean relatedness for a selection of random
individuals representative of the population (Burland ct al. 2001, Kimwele and Graves

2003, Matocq and Lacey 2004). This last method, the one we employed, is preferable

10

due to the opportunity to increase both the sample size of the ‘outgoup’ and the
independence of samples used to calculate both the within groups and the ‘outgroup’
estimate. Thus, to detect female-based kin groups in common eiders in this study, we
tested mean estimates of coefficients of relatedness among pairs of females within
designated groups against the background levels of female relatedness for the entire
colony. In addition, we tested mean estimates of coefficients of relatedness among pairs
of females within designated groups (arriving groups, nesting groups and females
departing together in groups) against mean estimates of coefficients of relatedness
among pairs of females between groups. When results between these two methods
conflicted, a greater emphasis was placed on the method using the background samples
as the outgroup due to the increased sample sizes and increased independence of
samples.

Background levels of female relatedness for this study colony were determined
by sampling females upon arrival to the colony. In panmictic populations, the
distribution of relatedness values across all pairwise comparisons will be normal with a
mean of zero. In philopatric colonial nesting species, higher mean background levels of
relatedness between individuals may occur due to natal philopatry. It was therefore
necessary to select a random sample of individuals representative of the population and
calculate background levels of female relatedness for the colony prior to testing for
female-based social groups.

Sampling of females was conducted in such a manner as to fulfill 2 fundamental
requirements. First, by selecting a large number of females (n=167) coming onto the

colony over the entire arrival period, we captured the genetic diversity of the entire

11

breeding population. Secondly, we systematically sampled across the entire pre-laying
and early incubation period in order to accurately represent the background levels of
relatedness for the colony by including early, mid and late nesters in the sample. A
large and temporally representative sample size typically means that estimates of allele
frequencies and estimates of coefficients of relatedness were unbiased. In addition, the
background estimate is independent of all other females used in subsequent analyses.
Male and female common eiders were caught in large nylon salmon gill nets (6m
tall by 100m long; Figure 2) erected on the colony during the prelaying and early laying
period (June 14 through July 4 2003). Nets were set in the flight paths of common
eiders flying around the seaward edge of the colony. A maximum of 2 nets were set
simultaneously. At one location, 2 nets were set perpendicular to each other, permitting
the capture of birds flying in from 2 different directions. At this site, eiders generally
arrive in mixed sex flocks varying in size from 2 to 30 birds. Females flew into the nets
first followed closely by the attending males. All captured individuals were banded with
metal bands on one tarsus. In addition, plastic alpha-numeric field readable color bands
were placed on the same tarsus above the metal band and an additional full size plastic
alpha-numeric color band was placed on the opposite tarsus. Approximately 0.25 ml of
blood was taken from the tarsal vein of target samples using a 25 gauge needle and
capillary tubes. Blood samples were immediately transferred to a prc-labeled centrifuge
tube with lml of saline buffer (100mM Tris, pH 8.0, 100mM EDTA, 10mM NaCl, 0.5%
SDS) and stored at ambient temperature (2-5°C) until transfer to a freezer at the end of

the field season.

12

Migration/Colony Arrival

To estimate levels of relatedness between females in groups arriving to the
colony together, mean coefficients of relatedness between females within an'ival groups
were compared to the background levels of relatedness for the colony. In addition,
mean coefficients of relatedness between females within arrival groups were compared
to those between groups. Aggregations of females arriving together were caught in the
large mist nets during the prelaying and early laying period (June 14 through July 4
2003). Females were considered to be arriving in groups if they entered the net together.
Only individuals that were seen flying together in a cohesive group and were
subsequently captured together were considered arrival groups. This methodology is
unique in that it permitted us to capture the natural composition of a distinct group of
birds in flight. Blood was collected from individual females within groups (n = 16
groups) as described above. Blood samples from females captured within groups were
used exclusively to estimate mean relatedness of females arriving together in groups,
and were not included in the background levels of relatedness for the colony discussed

above.

Nest Site Selection

To test whether females selected nest sites based on proximity to kin, mean
coefficients of relatedness were estimated between focal females (defined below) and
nearest neighbors during nesting, and these were compared to the background levels of
relatedness for the colony. In addition, mean coefficients of relatedness between focal

females and nearest neighbors (<50m apart) during nesting were estimated and compared

13

 

 

 

 

FRONT VIEW

salt water (east bay)

I freshwater pond

 
 

PROFILE

Figure 2: Front view and profile of nylon salmon gill net suspended between 2 metal
poles used to capture common eiders in flight upon arrival to the colony.

to estimates of relatedness between females nesting at greater distances compared to
estimates of relatedness between females nesting at greater distances from each other
(>100m apart). We monitored the location and timing of nest initiation of female eiders
in two 0.175 ha study plots. The two study plots were located in low and high density
nesting areas and were approximately 100m apart from each other. Detailed maps were
constructed for each monitored plot and nest locations were plotted for each female.
Approximate distances between nesting females were estimated. Plots were monitored
twice daily for the presence of nesting females from June 19th until August 8th 2003.
Nest initiation date was recorded only after a female had been present on the same nest
for at least three consecutive observation periods (approximately 1.5 days). Initiation
dates, presence of attending males and/or females, hatch dates and number of ducklings
departing the nest were recorded for each monitored nest. Nesting females were
categorized as early, mid or late nesters based on the distribution of nest initiation dates
for each plot.

Focal females were randomly selected from each of these categories using a
random number generator in Excel 2000. Plot maps were then used to select the three
nearest neighbors that were present prior to nest initiation of each focal female.
Therefore, a nearest neighbor female had to be present in the study plot when the focal
female initiated nesting. When approximately 80% of females in the study plots had
departed the nest, nests were visited for collection of feathers for use in genetic analysis.
In cases where nest material was not available for one or more of the nearest neighbors,
additional females were chosen based upon the same criteria until 3 nearest neighbors

were sampled. Due to the potential for the collection of feathers from more than one

15

female from the same nest, only samples that were consistent with one individual
genotype across all loci were included in the analyses. A total of 13 focal females, each
with three nearest neighbors, met this conservative criteria. This method was repeated
using a larger selection of focal females (n=28) that had only two nearest neighbors
available. Due to increased sample size when using only 2 nearest neighbors, analyses

were also conducted separately for high and low density nesting areas.

Colony Departure

To estimate levels of relatedness between females in groups departing the island
together with young, mean coefficients of relatedness between females within groups
departing together were compared to the background levels of relatedness for the colony.
In addition, mean coefficients of relatedness between females within groups departing
together were compared to those between groups. Females departing the island together
in groups were captured from July 24 through August 2, 2003. Two 8m x 8m x 4m wire
walk-in traps were constructed and placed on the shore of the island (Figure 4). As
groups departed, they were funneled into the walk in traps via 50 m lengths of 0.5m high
chicken wire fencing that extended at 45 degree angles from the trap entrances. Traps
were checked at two hour intervals and females and ducklings captured were handed and

bled as above. Groups (11 = 11) ranng in size from 2 to 5 females with 3 to 20 juveniles

Genetic Analysis

DNA was extracted from all blood samples using QIAGEN DNEasy ® extraction kits.

DNA was quantified using a spectrophotometer and diluted to 20ng/pl for amplification.

l6

DNA was extracted from all feather samples in the same manner. Only five contour
feathers were used per nest due to the potential for genetic contamination (i.c. feathers
from different individuals in the same nest). Reducing the number of feathers selected
can reduce the potential for contamination (Pearce et al. 1997). Extracted feather samples
were amplified undiluted due to low concentration of DNA. DNA was amplified using
Polymerase Chain Reaction (PCR) for 10 microsatellite loci: SfiuS, Alau1(Fields and
Scribner 1997), Sfip9, SfiulO and Sfiull (Libants et al. unpub), HhipS, Bcaull
(Bucholz et al. 1998), Smou4, SmoulO (Paulus and Tiedemann 2003) and Aphp23
(Maak et al. 2003). All loci were run under published PCR conditions with slight
modification (Table 1). Due to the low concentration of DNA extracted from the feather
samples, feather samples could not be reliably amplified at 2 of these loci (Sfiull and
SfiuS). PCR products were run on 6% denaturing acrylamide gels along with a molecular
base pair ladder and standards of known size. Gels were scanned with a Hitachi FMBIO
II scanner. Alleles were hand scored for each individual. Initial allele scores were double
checked by a second experienced lab member. Approximately 8 to 10% of samples were
rerun across all loci to test for genotyping error.

To obtain background allele frequencies for the populations, a total of 167
individuals were selected systematically from all females caught in the net (not including
those within arrival groups) representing the entire range of arrival times for all females.
Estimates of allelic frequencies were generated in the program Microsatellite Analyzer
(MSA), version 3.15 (Dieringer and Schlotterer 2002). Allelic richness and observed and
expected heterozygosity were calculated using the program Genepop, version 3.3

(Raymond and Rousset 1995). Tests for deviation from Hardy Weinberg equilibrium and

17

45 cm

 

’ Door

Flap

F igurc 3: Walk-in wire nest trap used to capture females on the nest during incubation
(modified from Weller 1957).

18

an

 

 

lnm

 

   
 
   
 
  
 

  
 
 

c

.. o'o’o‘c’c’o’o ’
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groups.

Figure 4: Wire walk-in trap used to capture females and young departing the island in

19

tests for linkage disequilibrium between loci (Bonferroni corrected (Rice 1989) to adjust
nominal alpha levels for multiple testing) were also conducted using the program
Genepop, version 3.3 (Raymond and Rousset 1995).

Pair-wise coefficients of relatedness were calculated using the program Kinship, version
1.3.1 (Goodnight and Queller 1999). Pair—wise coefficients of relatedness provide a
measure of relatedness between two individuals, and are estimated based on the
proportion of alleles shared between individuals adjusted based on population allele
frequencies. Estimates are therefore non-independent and standard parametric statistics
cannot be used to detect differences in mean relatedness between groups. Instead,
differences in mean pair-wise coefficients of relatedness between groups were
determined via one-tailed permutation tests in SAS with 1000 repetitions (Ratnayeke et
al. 2002). Permutation tests calculate an observed difference between the means of any
two groups, pool the data from both groups, then randomly sub-sarnple two new groups
and calculates the difference in mean relatedness between the two new groups. The
probability of the new theoretical difference being greater than the observed difference is
then calculated based on 1000 repetitions. Permutation tests were used to detect
differences in mean pair-wise coefficients of relatedness between females within groups
to those between groups.

To provide a description of group composition in terms of relatedness between
individuals within groups, we further estimated the likelihood that alleles between
individuals were identical by descent using the program Kinship, version 1.3.1.
Specifically, we tested competing hypotheses regarding specific pedigrees. We tested

whether coefficients of relatedness were significantly more likely under the hypothesis of

20

Table 1: PCR was carried out in 25 ul volumes, using 1pmol primer, PCR buffer [IOuM
Tris Cl pH 8.5, 1.5uM MgC12, 100ug/ul BSA, 0.0025% Tween 20, SOmM KCl], 200uM
dNTP and 0.5 U of Amplitaq DNA polymerase (Perkin Elmer). Modifications from
published PCR conditions are listed by locus.

 

 

 

Locus Ta (°C)j Cycles2 Mgle %DMSO
Alau14 47 35 1.5mM 0.6
Aphu23 56 35 2.5mM 0
Bcaull 57 30 1.5mM 0.8
Hhip.5 54 35 1 .5mM 0
Sfius 51 35 3mM 0.8
$111.19 51 35 2.5mM 1
Sfi“ 10 50 35 3mM 0
Sfipll 50 35 2.5mM 0.4
Smo “4 48 35 1.5mM O
Smoul 0 50 35 1.5mM 0
' Annealing temperature

2 1 cycle consisted of 1:00 minute at each of denaturing, annealing and extension temperatures

3 Total MgClz including the amount mentioned for the standard recipe

‘ Alaul required an alternate PCR buffer : [10 pM Tris Cl pH 8.3, 1.5mM Mg C12 , 100pg/pL gelatin, 0.01

% NP 40, 0.01% Triton X-100, SOmM KCl].

21

mother offspring or full-sibling relationships (er = 0.50; hereafter full-sibling equivalent)
or half-sibling relationships (er = 0.25) than under the alternative hypothesis of 2
individuals being unrelated (rxy = 0). The program Kinship calculates the probability of
finding observed genotypes consistent with these pedigrees given population allele
frequencies. Significance tests were based on simulations and estimates of statistical
power were based on the number of loci combined with heterozygosity of each locus

(Goodnight and Queller 1999).

22

RESULTS

Genetic Analysis

Allelic frequencies, allelic richness, and observed and expected heterozygosity for
each locus were high (Table 2). The mean number of alleles per locus was 12.4 (SD =
3.16, range 4 to 33) (Table 2). Genotypic frequencies of 8 loci were consistent with
expectations of Hardy Weinberg, whereas genotypic frequencies at two loci (Smop4 and
HhiuS) were not consistent with Hardy Weinberg expectations. Smou4 was highly
polymorphic (33 alleles) (Table 2). The background sample size (n=167) was not large
enough to represent the full range of possible genotypes (531) for such a polymorphic
locus; a common problem when estimating population gene frequencies from samples
(N ei 1987). However, Smou4 and Hhiu5 were included in both estimates of coefficients
of relatedness, and likelihood tests of pedigrees, as the deviation from Hardy Weinberg
expectations were either minimal (Hhiu5) and/or due to small samples (Smou4) and
consequently would not likely bias estimates. Tests for linkage disequilibrium confirmed

that all loci were independently inherited.

Background levels of female relatedness in the colony

Background levels of female relatedness in this colony indicate a panmictic
population with a normal distribution of rxy values (Figure 5) with a mean close to zero
(mean rxy = -0.004) (Table 3). A mean r.y of zero for the background level indicates that,

on average, females in the colony are not related to one another.

23

Table 2: Allelic Richness and Observed and Expected Heterozygosity for background
samples at 10 polymorphic loci.

 

 

 

Locus Het obsl Het exp2 F3 Allelic Richness
SfiplO 0.813 0.855 0.049 23
Sfiu9 0.714 0.744 0.040 8
Alaul 0.652 0.631 -0.034 6
Hhiu5 0.103 0.122 0.153 4
sfiuS 0.730 0.769 0.052 16
Sfiull 0.462 0.460 -0.012 6
SmoplO 0.813 0.801 -0.014 18

Aphu23 0.613 0.586 -0.046 6
Smou4 0.850 0.943 0.099 33
Bcaull 0.130 0.130 -0.007 4
Mean 0.588 0.603 0.026 12.4

1 Observed heterozygosity

2 Expected heterozygosity

3 Deviation from Hardy Weiberg equilibrium, positive values indicate heterozygote deficiency, negative
values indicate heterozygote excess

24

Table 3: Mean pair—wise relatedness values as calculated in Kinship 1.3.1 (Goodnight and
Queller 1999) for all groups and results of one-tailed permutation tests (Ratnayeke et al.
2002) testing for differences between mean relatedness of females in groups versus
background levels.

 

 

 

 

Group Sample Size Mean pair-wise Permutation
relatedness values test
p-value
Background (10 loci) 167 0004
Arrival groups 16 0.069 0.012
Background (8 loci) 167 -0.006
Focal females and 3 13 0.060 0.039
nearest neighbors
Focal females and 2 28 -0.003 0.482
nearest neighbors
High Density 10 0.080 0.044
Low Density 18 -0.050 0.873
Background (10 loci) 167 -0.004
Departing Broods 11 0.055 0.047

 

25

Migration/Colony Arrival

We tested the hypothesis that aggregations of female common eiders were
composed of related individuals during colony arrival and inferentially that female kin-
based social bonds exist in common eiders during colony arrival and migration from the
wintering grounds. The mean estimates of pair-wise relatedness for females within
arriving groups (er = 0.069) was significantly greater than was estimated for the mean
background level of relatedness for the colony ( rxy = 0004; permutation test, p = 0.034)
(Table 3). In addition, the mean estimate of pair-wise relatedness for females within
arriving groups (er =0.069) was significantly greater than that between groups (er = -
0.017; permutation test, p = 0.008) (Table 4). The distribution of pair-wise relatedness
values for the arrival groups are shified towards more positive values than the
background levels (Figure 5A) indicating that aggregations of females during colony
arrival are composed of related individuals. Estimates of relatedness consistent with full
sibling equivalent relationships (rxy = 0.50) were present in 4 of 16 arrival groups (O.<
0.05, B = 0.044). Included in these groups was one group of 4 females with 3 full sibling
equivalent relationships. Thus, the null hypothesis that female associations present at the

time of colony arrival are random was rejected.

Nest Site Selection
We tested the hypothesis that aggregations of female common eiders were
composed of related individuals during nesting. When focal females initiated nests, there

was an average of 32 (SD = 4.8, range 16 —- 83) females nesting in the study plots.

26

Table 4: Mean pair-wise relatedness values as calculated in Kinship 1.3.1 (Goodnight and
Queller 1999) for all groups and results of one-tailed permutation tests (Ratnayeke et al.
2002) testing for differences in mean relatedness within versus between groups.

 

Mean pair-wise Mean pair-wise
relatedness values relatedness values Permutation test
Group Sample Size (within groups) (between groups) p-value

 

Arrival groups 16 0.069 -0.017 . 0.008

 

Focal Females and

 

3 nearest neighbors 13 0.061 -0.038 0.007

Focal Females and

2 nearest neighbors 28 -0.003 -0.029 0.216
High Density 10 0.080 -0.029 0.019
Low Density 18 -0.050 -0.029 0.725

Departing groups 11 0.055 0.020 0.173

 

27

El Background Level

0'2 IArrival Groups
5
c 0.15 1
o .
3
U' 1
2 0.1 .
u- l
0.05 ~,
or chcd 22L
N 0
‘ 9 9°° 9-" 9'” 9L 9-“ 9 9- A
Coefficient of Relatedness
0.25 , DBackground Levels
1
0.2 . lFocaI Females and3
> ‘ Nearest Neighbors
2 0.15 t
w
3
3 0.1«
LL 1
°°' fl 1 1
o la Haul]- . , _ fl ,1..- _
5993999129'1' QQWQhO‘bQfib N
Coefficient of Relatedness B
0.35 ‘ DBackground Level
0.3 i, IDeparting Groups
>. 0.25 i
‘e‘
e 0.2 l
a .
g 0.15
.L 1

9
—l

M: __nflfl flea---

9$9©9P990030P§§>5C

Coefficient of Relatedness

Figure 5: Distribution of relatedness values A) between females within arriving groups,
B) between females and 3 nearest neighbors and C) between females in departing groups
set against background levels of relatedness for the colony.

28

Nearest neighbors initiated nests on average, 2.6 (SD = 0.44, range = 0-13) days before
focal females initiated nests. The mean estimate of pair-wise relatedness for focal
females and their three nearest neighbors (er = 0.060) was significantly greater
than the mean background level of relatedness for the colony (er = -0.006; permutation
test, p = 0.012) (Table 3) indicating that aggregations of females during nesting were
related to each other. The distribution of pair-wise relatedness values for the focal
females and three nearest neighbors were shifted towards more positive values than the
background levels (Figure 5B), indicating that aggregations of females during nesting
were composed of related individuals. In addition, the mean estimate of pair-wise
relatedness for focal females and their three nearest neighbors (r.y = 0.061) was
significantly greater (permutation test, p = 0.007) than that between females nesting at
greater distances from each other (er = -0.03 8) (Table 4). Two focal females had 2 full
sibling equivalent relationships with their nearest three neighbors (p< 0.05, B = 0.101).
Another 3 focal females had 1 full sibling equivalent relationship within the nearest three
neighbors (p< 0.05, [3 = 0.101). An additional 2 focal females had half siblings (er =
0.25) within the nearest three neighbors QJ< 0.05, B =0.48l). Thus, a total of 7 of 13
focal females had at least half siblings within the three nearest neighbors. The null
hypothesis that female associations during nest site selection are random was rejected.
When the number of nearest neighbors nesting in both high and low densities was
reduced to two (and the sample size was increased to n=28 focal females), the mean pair-
wise relatedness between focal females and nearest two neighbors (er = -0.003) was not
significantly greater than that for background levels (er = -0.006) for the colony

(permutation test, p = 0.482) (Table 3). Additionally, the mean estimate of pair-wise

29

relatedness between focal females and the nearest two neighbors (er = -0.003) was not
significantly greater than that between females nesting at greater distances from each
other (er = -0.029; permutation test, p = 0.216) (Table 4). This suggests that tighter
aggregations of females during nesting may not related to each other. However, when
focal females were grouped by nesting density, the mean estimate of pair-wise
relatedness between focal females and the nearest two neighbors in high density areas (er
= 0.080; n= 10 focal females) was significantly greater than both the background levels
(rxy = -0.006; permutation test, p = 0.044) and that between females nesting at greater
distances from each other (er = -0.029; permutation test, p = 0.019). In contrast, the
mean estimate of pair-wise relatedness between focal females and the nearest two
neighbors nesting in low density areas (er = -0.050; n= 18 focal females) was not
significantly greater than the background levels (rxy = -0.006; permutation test, p = 0.873
) or that between females nesting at greater distances from each other (rxy = -0.029:
permutation test, p = 0.725). These findings suggest that levels of relatedness are greatest

among females nesting at high densities in close proximity to each other (Table 4).

Colony Departure

I tested the hypothesis that aggregations of adult female common eiders departing
the colony with young were composed of related individuals. Mean departing group size
was 11.33 (SD = 5.80, range 5-23). The average number of adult females per departing
group was 2.40 (SD = 1.24, range 1-5), and the average number of ducklings was 8.93
(SD = 1.28, range 4-20; Table 5). The average ratio of ducklings to adult females in

captured groups was 3.72:1. The mean estimates of pair-wise relatedness for adult

30

females in departing groups (er = 0.055) was significantly greater than that for the mean
background level of relatedness (er = -0.004; permutation test, p = 0.047) for the colony
(Table 3, Figure 5C). The distribution of pair-wise relatedness values for the departing
groups are shifted towards positive values than the background levels (Figure 5C),
indicating that aggregations of females during colony departure are composed of related
individuals. Thus, the null hypothesis that female associations present at the time of
colony departure are random was rejected.

The mean estimates of pair-wise relatedness for females in departing groups (er
= 0.055) was not significantly greater than that for females between groups (er = 0.020;
permutation test, p = 0.173) (Table 4). Despite this, full sibling equivalent relationships
were still found between females in two departing groups. One departing group had 2
full sibling equivalent relationships (p< 005,13 = 0.052) between adult females and a
second departing group had 1 full sibling equivalent relationship (p< 0.01, B = 0.163)

between adult females.

31

Table 5: Composition of departing groups captured
in walk in traps during colony departure.

 

Total Total
Date Captured Group Size Adults Young

 

l9-Jul 8 2 6
22-Jul 6 2 4
22-Jul 7 1 6
23-Jul 13 S 8
26-Jul 12 2 10
28-Jul 7 1 6
23-Jul 23 3 20
24-Jul 8 2 6
26-Jul 17 3 14
27-Jul 8 2 6
28-Ju1 15 3 12
29-Jul 5 1 4
29-Jul 5 1 4
31-Jul 21 4 1 7
31-Jul 15 4 1 1

 

Mean (SD) 11.33(5.80) 2.40(1.24) 8.93(4.96)

32

DISCUSSION

Documentation of spatially juxtaposed kin groups during migration, nest site
selection, and colony departure has resulted in rejection of the null hypothesis that social
groups in common cider females are random with respect to relatedness. When
compared to mean estimates of inter-individual relatedness for the entire colony,
significantly high levels of relatedness were found between females within arriving
groups, between females and nearest neighbors at the time of nest site selection and
between females within departing groups. Collectively, these results provide evidence for
kinship-mediated sociality in common cider females beyond that which has been

previously documented.

Migration/Colony Arrival

Andersson and Wallander (2004) hypothesized that the “v” formation of flight in
many migratory birds occurs in species migrating in kin groups. The “v” formation is
common within the tribe Anserini (Gould and Heppner 1974) in which kin groups have
been documented during migration (review in Elder and Elder 1949, Raveling 1969,
Prevett and Mclnness 1980, Scott 1980). Common eiders migrate in more dynamic bow-
shaped flocks with energy-saving dynamics presumably similar to those of the “v”
formation (Alerstam 1990) and thus have been suggested as an additional example of kin-
bascd cooperation during migration. Though the data reported here do not directly detect
kin groups during long-distance migration, the flocks of eiders were caught in flight at

the time the individuals arrived at the colony; whether it be from a nearby foraging area

33

or from the wintering grounds. It is likely, therefore, that female associations represent
an extension of coalitions existing at earlier stages, such as on the wintering grounds as
described in some species of geese and swans which winter in family groups (Raveling
1969, Raveling 1979, Scott 1980, Ely 1993).

The confirmation of female kin groups arriving in flight together at the breeding
colony provides the first direct evidence for stronger female-female bonds than has been
previously documented in seaducks. The presence of full sibling equivalent relationships
suggests that offspring follow the females (and/or siblings) from hatch, beyond the brood
rearing period, throughout the fall moult and migration to wintering areas, and during
return to the colony. This has not been previously observed in tribe Mergini. Evidence of
family-like groups (young with adults) has been suggested for another seaduck, the
harlequin duck (Histrionicus histrionicus; Regehr et al. 2001, Cooke et al. 2000) and
geese (Elder and Elder 1949) based on sightings of juveniles arriving with adults on the
wintering areas. Relationships, however, have not previously been confirmed
genetically.

In addition, our detection of half sibling relationships (er = 0.25) indicates that
these family groups can persist across several years or across extended family members.
An r,‘y value of 0.25 can be explained through a variety of mechanisms including, but not
limited to, an offspring following other female relatives, young from multiple years
following a mother, or multiple paternity in a clutch (Hario et al. 2002). Prolonged (>2
years) mother/offspring and sibling relationships have not been commonly observed in
Anseriformes (Black and Owen 1989, Prevett and Maclnnes 1980, Raveling 1979, review

in Owen 1980). Though patterns of prolonged parent-offspring bonds and extended

34

family units have been documented in migrating geese (Ely 1993, Warren et a1. 1993)
and swans (Scott 1980), these studies were based on behavioral observations or visual
observations of banded individuals, and lacked genetic confirmation of mother/offspring
and sibling relationships.

Observations of family groups in the absence of genetic relatedness data are no
longer sufficient to describe family units due to the high prevalence of intra-specific
brood parasitism (Anderson et al. 1992) and extra pair copulations in Anseriformes
(Westncat and Stewart 2003). For example, in the absence of genetic data, one of the
arrival groups captured in this study would have been documented as a likely mother
offspring group. In Common Eiders, body mass upon arrival can be an indicator of
breeding condition (Milne 1976). In one of the anival groups, one of the females
(2140g) would have been classified as being in prime breeding condition, while the other
female (1560g) would have been classified as a non-breeder. These individuals could be
misclassified as a mother/offspring pair based on body condition alone. However,
coefficients of relatedness between the two individuals were 0.063, indicative of a non-
familial relationship. Here, we present the first genetic evidence of mother/offspring or
sibling bonds in flight and the first genetic evidence of potential prolonged or extended

family relationships for common eiders specifically, and Anseriformes in general.

Nest Site Selection

Kin clustering during nesting has been documented among many species (e.g.,
Burland et a1. 2001, van der J eugd et al. 2002, Ratnayeke et al. 2002). These studies,

however, only identified general spatial patterns of relatedness in breeding areas (i.c.,

35

correlation of relatedness and geographic proximity). Previous studies did not examine
the decision making process during nest site selection by individual animals. Female
common eiders investigate several nest sites, often sitting in them, before choosing the
final nest cup (pers obs and Cooch 1965, Schmutz et al. 1982). By examining the levels
of relatedness between focal females and their nearest neighbors at the time of nest site
selection, we have confirmed a preference for nesting in proximity to kin. Given the
abundance of females nesting in these areas when focal females selected nests, and the
high prevalence of full and half sibling equivalent relationships between focal females
and their three nearest neighbors, there is strong evidence that kinship is a factor in nest
site selection. When the number of nearest neighbors was reduced to two, the same
trend occurred only in high density areas. This might be explained by a higher level of
human disturbance in the low density area during mid to late laying due to another study
which required the collection of males attending laying females.

Given evidence of kin groups in arriving females, it is not surprising to find
higher levels of relatedness between nesting females and their nearest neighbors. If
females are arriving together it is possible that they may be selecting nest sites at the
same time, in the same locations based on other ecological factors such as proximity to
water, distance to predators nests and characteristics of available nest cups themselves
(Kilpi and Lindstrom 1997). Females arriving together may nest together in the highest
quality areas available at the time of arrival. However, the nearest neighbors selected in
this study initiated nests, on average, 2.6 days earlier than the focal females; clearly
indicating separate nest initiation times. In addition, females arriving together in groups

can vary in breeding condition. For example, of females caught in the net at the same

36

time, some laid an egg while in the holding box within an hour, whereas others
prospected for nesting areas for several days before finally selecting a nest site and
laying. This suggests that although individuals may arrive together, nesting among
related individuals is not necessarily synchronous, and therefore it is unlikely that these
patterns are solely an artifact of similar colony arrival times. Based on the design and
results of this study, it is more likely that there is some level of kin recognition among
female common eiders; the mechanisms of which remain poorly understood in common
eiders and in birds in general (Komdeur and Hatchwell 1999). However, our findings do
support some form of kin recognition and preference for proximity to kin during nest site
selection.

Female phi10patry might also account for higher levels of relatedness between
nearest neighbors. Common eiders are philopatric to nesting areas within colonies (Cooch
1965) and fidelity to specific nest sites, though rare, has been documented (Goudic et al.
2000). Natal philopatry could explain close proximity of kin in nesting areas regardless of
nest site selection processes. Studies conducted on other seabird colonies (Great
Cormorants (Phalacrocorax carbo): Schjorring 2001, Blue-footed Boobies (Sula
nebouxii): Osorio-Beristain and Drummond 1993) have shown that individuals showed a
greater preference for nesting in proximity to natal nesting areas as opposed to kin. These
species, however, exhibit both male and female philopatry and pair bonds form on the
breeding grounds. Nesting in close proximity to kin could be detrimental in species where
both sexes are highly philopatric and breeding colonies are small in number due to
increased risk of inbreeding. In common eiders, only females are philopatric and pair

bonds are thought to form on the wintering grounds. Consequently, the process of

37

selecting nests in close proximity to kin, does not afford the negative consequences of
inbreeding for common eiders. In addition, van de J eugd et al. (2002) documented a
preference for nesting in close proximity to kin in a philopatric species (Barnacle geese,
Branta leucopsis) even when nesting away from natal colonies.

Though we had sufficient power to detect relatedness between focal females and
nearest neighbors, it should be noted that this study likely under-estimates the degree of
relatedness among groups of nesting eiders due to limitations during sampling. Sample
sizes of focal females could have been greatly increased had eiders been sacrificed.
Instead, nest material was collected from each neighboring nest once 80% of the females
had departed the plot. Thus, nearest neighbors selected for this study were the closest
neighbors present at the time of focal female nest selection that also had sufficient nest
material to permit genotyping. If nests had been visited earlier in incubation, we would
have been able to collect genetic material from the true nearest neighbors. However, this
would have increased nest abandonment because eiders are extremely sensitive to nest

disturbance, particularly during early incubation (Choate 1967, Criscuolo 2001).

Colony Departure

Relatively higher levels of relatedness between females in departing groups could
be a result of arrival in kin groups, nesting in kin groups or a combination of both. If
females are arriving together, they may be nesting at the same time and consequently
clutches would hatch synchronously and females would depart with young at the same
time. It is likely then, if brood amalgamation is to occur, that females in departing

groups may be relatively closely related to each other due to timing of arrival and nesting.

38

The accidental mixing hypothesis partially explains this phenomena in breeding females
(Munro and Bedard 1977b, Warhurst and Bookhout 1983, Eadie et al. 1988) where there
is a propensity for broods to amalgamate accidentally due to high brood density
(Patterson et al. 1982, Savard et al. 1989, Warhurst and Bookhout 1983) and/or during
the confusion of a predation attack from gulls (Munro and Bedard 1977b). Associations
of adult females that amalgamate broods could be random due to accidental mixing of
young, but patterns of relatedness would still exist due to higher relatedness between
females that arrived together in the same breeding condition, and thus were departing the
island at the same time. However, not all female associations during colony departure
occur as a result of the accidental mixing of broods. Females with no young of their own
also accompany departing groups. Satellite telemetry data from our field site indicates
that many non-breeders or failed breeders remain near the colony, feeding in the bay,
throughout the breeding season (Gilchrist unpubl. data). These females routinely return to
the colony during late incubation periods and attend incubating females (Gilchrist unpubl.
data, Schmutz et al. 1982, Munro and Bedard 1977a). These non-breeders or failed
breeders will join incubating females at the nest just prior to hatch (usually 24 hours
prior) (Schmutz et a1. 1983, Munro and Bedard 1977a, Bustnes and Erikstad 1991b), and
escort the brood from the nest site to the marine habitats.

The presence of failed or non-breeders in amalgamated broods might be explained
by female nest site selection, prolonged female offspring or sibling bonds or female
philopatry to natal nesting areas. When nesting attempts fail, females depart the breeding
area to recover nutritional reserves (Gorman and Milne 1972). If failed breeders tend to

select nests in close proximity to kin because female associations are strong, failed

39

breeders would likely return to attend broods in the same area of their failed nesting
attempt as opposed to a foreign area in the colony. The same trend might occur due to
female philopatry to nesting areas. If siblings are nesting in proximity to each other due
to returning to similar nesting areas, they may also be attending broods in the same areas
for the same reason.

It is unknown why females return to the colony after a failed nesting attempt.
The experience hypothesis (Eadie et al. 1988) suggests that failed breeders may return to
the colony to identify successful nesting areas. Reproductive success in eiders however
is more likely due to body condition upon arrival rather than area of nesting (Erikstad et
al. 1993, Erikstad and Tveraa 1995), although the influence of previous experience at a
nesting location remains unknown. For non-breeders, generally young birds, the
experience hypothesis suggests that non-breeders are in the process of learning how to
rear young and obtain information on valuable foraging and moulting areas. Thus,
patterns of relatedness in departing groups that we detected in this study could be partly
explained by female philopatry to natal nesting areas.

The adaptiveness of attending departing groups with relatives for a failed or non-
breeder could be explained by kin selection if duckling survival was enhanced by this
attendance. Campbell (1975) suggests that the time period between hatching and
departure from the nest (24 hours), not the departure itself, is the period of greatest
predation risk for ducklings, with 27.8% of nests with eggs being attacked compared to
78% of nests with ducklings being attacked (Campbell 1975). At the East Bay cider
colony, attending females tend to arrive at the nests of incubating females 1.86 days

before departure, precisely during this critical hatching period. Their presence at the nest

40

may decrease predation pressure because we have observed attending females defending
nests against gull attacks. Despite evidence of vigilant behavior by failed or non-
breeders during predation attacks on ducklings (Schmutz et al. 1982), increases in
duckling survival due to these attending females, is uncertain (Campbell 1975, Ahlen and
Andersson 1970).

Intense social interactions between common cider females begin during the first
few days following hatch (Ost and Kilpi 2000). By capturing females and ducklings in
broods during departure from the island itself and prior to the formation of stable creches
we have generated the first genetic information confirming kin relationships between
females early in coalition formation. Although there was the potential for biases in
composition of groups captured due to the nature of the walk-in traps and the varying
cohesiveness of departing groups (i.c., some females were more likely to stay with the
group). Some females did not enter the traps with the brood and thus we did not always
have the full sample of females in the original departing broods. However, trap avoidance
would have biased the results in a manner making the null hypothesis more difficult to
reject. In addition, though traps were checked every two hours, it is possible that more
than one amalgamated brood may have entered the trap at the same time. We found that
this did not likely occur as the ratio of ducklings to females in captured broods (3.72: 1)
was consistent with those recorded for naturally occurring departing broods in other
studies (Gorman and Milne 1972, 3.5:1; Ost 1999,5:1; Swennen 1989, 2.1-3.1:1).

Ost (1999) found the number of females in departing groups was most variable
during peak hatch and as the season progressed, groups composed of two females and

attendant young were the most stable coalitions. We captured broods throughout the peak

41

hatch period. Though we were interested in investigating relationships between females
early in coalition formation, if the true nature of kin groups in amalgamated broods were
only reflected in the relationships between 2 adults we may have diluted this effect by
including early transient females (Ost et al. 2003). If relationships between only two
females within the group are most important, we could have even stronger results if

female relatedness in stable crechcs were investigated following colony departure.

Conclusions

Group existence and social behaviors have evolved due to increased fitness of
individuals in groups (Alexander 1974). Our findings confirmed that, at this colony,
some common cider females form kin-based social groups during colony arrival, while
nesting, during colony departure, and thus potentially year round. Based on relatively
high levels of relatedness within these female social groups, our study indicates that the
benefits of sociality in common eiders may accrue via kin selection. However, kin
selection cannot be confirmed solely on the basis of high level of relatedness between
individuals (Griffin and West 2002), because measures of both direct and indirect fitness
benefits need to be considered.

Throughout each of several stages, colony arrival, nesting and brood rearing, we
have provided evidence of sociality and kin groups in common eiders. Though we have
not measured direct or indirect associated fitness benefits, previous avian studies have
indicated possible fitness benefits of sociality and kin groups during migration (Alerstam
1990), nesting (van der J eugd 2002) and brood amalgamation (Ost et al. 2002, Munro and

Bedard 1977b). Benefits of prolonged female bonds in common eiders might include an

42

increase in individual adult survival due to increased group size. For example, larger
group size on the wintering grounds could increase survival via therrnoregulatory benefits
during roosting (Gilchrist and Robertson 2000) and/or by lowering predation risk by
vigilance and dilution effects. However, indirect benefits may be reduced via increased
competition between relatives (Griffin and West 2002). Our evidence of kin groups in
several stages throughout the breeding season suggest that kin selection is a valid
hypothesis to support the adaptiveness of group behaviors in the common cider.

Female kin associations confirmed in this study may also be a driving force in the
evolution of life history traits such as delayed reproduction, longevity and iteroparity
among common eiders and other Anseriformes. Decisions regarding reproduction in
arctic nesting species clearly portray the 'tradeoff between current and residual
reproductive success (Erikstad and Tveraa 1995, Erikstad ct a1. 1993). Common cider
females experience severe incubation costs (Milne 1976, Korschgen 1977, Parker and
Holm 1990, Bottita et al. 2001), and nest or brood abandonment likely increases lifetime
fitness despite loss of the current clutch (Coulson 1984, Bottita et al. 2001). Increased

sociality in common cider females may buffer the severity of these tradeoffs.

43

LITERATURE CITED

Ahlen, I. and A. Andersson. 1970. Breeding ecology of an cider population on
Spitsbergen. Ornis. Scand. 1:83-106.

Alerstam, T. 1990. Bird Migration. Cambridge University Press, Cambridge.

Alexander, RD. 1974. The evolution of social behavior. Ann. Rev. of Ecol. Syst. 5:325-
383.

Andersson, M. and Wallander, J. 2002. Kin selection and reciprocity in flight formation.
Behavioral Ecology 15(1): 158-162.

Anderson, M.G., Rhymer, J .M and F .C Rohwer. 1992. Philopatry, Dispersal and the
genetic Structure of Waterfowl Populations. In Batt, B.D.J., A.D. Afton, M.G. Anderson,
C.D. Ankney, D.H. Johnson, J .A. Kadlec and CL. Krapu. 1992. Ecology and

Management of Breeding Waterfowl. University of Minnesota Press.

Ashcroft, RE. 1976. A function of pair-bond in the common cider. Wildfowl 27:101-105.

Baillie, SR. and H. Milne. 1982. The influence of female age on breeding in the Eider
Somateria mollissima. Bird Study 29:55-66.

Bateman, A.J. 1948. Intra-sexual selection in Drosophila. Heredity 2:349-368.
Bergrnuller, R. and M. Taborsky. 2005. Experimental manipulation of helping in a
cooperative breeder: helpers ‘pay to stay’ by pre-emptive appeasement. Animal

Behaviour 69:19-28.

Black, J .M. and M. Owen. 1989. Parent-offspring relationships in wintering bamacle
geese. Animal Behaviour 37(2): 187-198.

Boos, J.D., Nudds, TD. and K. Sjoberg. 1989. Posthatch brood amalgamation by
Mallards. The Wilson Bulletin 101(3):503-505.

Brown, K. 1998. Proximate and ultimate causes of adoption in ring-billed gulls. Animal
Behaviour 56:1529-1543.

Buchholz, W.G., Pearce, J .M., Pierson, B.J., and KT Scribner. 1998. Dinucleotide
repeat polymorphisms in waterfowl (family Anatidae): characterization of a sex-linked

(Z-specific) and 14 autosomal loci. Animal Genetics29z322-332.

Burland, T.M., Barratt, E.M., Nichols, RA. and PA. Racey. 2001. Mating patterns,

44

relatedness and the basis of natal philopatry in the brown long-cared bat, Plecotus auritus.
Molecular Ecology 10:1309-1321.

Bustnes, JD and KB. Erikstad. 1991a. Parental care in the common cider Somateria
mollisima: factors affecting abandonment and adoption of young. Can. J. Zool. 1538—
1545.

Bustnes, J .O. and KB. Erikstad. 1991b. The role of failed nesters and brood abandoning
females in the creching system of the common cider somateria mollissima. Omis. Scand.
22:335-339.

Bustnes, J .O., Erikstad, KB. and TH. Bjorn. 2002. Body condition and brood
abandonment in Common Eiders Breeding in the High Arctic. Waterbirds 25(1):63-66.

Campbell, L.H. 1975. Predation on Eiders Somateria mollissima by the Glaucous Gull
Larus hyperboreus in Spitsbergen. Omis. Scand. 6:27-32.

Cezilly, F ., Tourenq, C. and A. Johnson. 1994. Variation in parental care with offspring
age in the greater flamingo. Condor 96(3):809-812.

Choate, J .S. 1967. Factors influencing nesting success of eiders in Penobscot Bay, Maine.
J. Wild. Manage. 31(4):769-776.

Clutton- Brock, T.H., O’Riain, M.J., Brothcrton, P.N.M., Gaynor, D., Kansky, R.,
Griffin, AS. and Manscr, M. 1999. Selfish sentinels in cooperative mammals. Science
284:640-1644.

Clutton-Brock, T.H., Russell, AF. and Sharpe, LL. 2004. Behavioural tactics of breeders
in c00perative meerkats. Animal Behaviour 68: 1029-1040.

Cooch, PG. 1965. The breeding biology and management of the northern common cider
in the Cape Dorset area, N.W.T. Canadian Wildlife Service. Wildlife Management
Bulletin 2(10).

Cooke, F ., Robertson, GI. and Smith, C. 2000. Survival, emigration, and winter
population structure of Harlequin Ducks. The Condor 102: 137-144.

Cooper, J .M. and Miller, EH. 1992. Brood amalgamation and alloparental care in the
Least Sandpiper, Calidris minutilla. Can. J. Zool. 70:403-405.

Coulson, J.C. 1984. The population dynamics of the Eider Duck Somateria mollissima
and evidence 0 f extensive non-breeding by adult ducks.

Criscuolo, F. 2001. Does blood sampling during incubation induce nest dcsertion in the
female common cider (Somateria mollissima)? Marine Ornithology 29: 47-50.

45

Curry, R.L. 1988. Influence of kinship on helping behavior in Galapagos mockingbirds.
Behavioural Ecology and Sociobiology 22: 141 -1 52.

Dieringer, D. and C. Schlotterer. 2002. Microsatellite Analyzer MSA: a platform
independent analysis tool for large microsatellite data sets. Molecular Ecology 3(1): 167-
169.

Eadie, J .M., Kehoe, F .P., Nudds, T. 1988. Pre-hat and post-hatch brood amalgamation in
North American Anatidae: a review. Can. J. Zool. 66: 1 709-1 721.

Eadie, J.C. and BE. Lyon. 1998. Cooperation, conflict and creching behavior in
Goldeneye ducks. The American Naturalist 151(5):397-408.

Elder, W.H. and N.L. Elder. 1949. Role of family in the formation of goose flocks. The
Wilson Bulletin 61(3): 133-140.

Ely. CR. 1993. Family stability in Greater White-Fronted Geese. The Auk110 (3):425-
435.

Erikstad, K.E., Bustnes, 1.0. and T. Moum. 1993. Clutch-size determination in precocial
birds: a study of the common cider. Auk 110:623-628.

Erikstad, BE, and T. Tveraa. 1995. Does the cost of incubation set limits to clutch size
in common eiders Somateria mollissima? Oecologia 103:270-274.

Fields, R.L. and Scribner, K.T. 1997. Isolation and characterization of novel waterfowl
microsatellite loci: cross-species comparison and research application. Molecular
Ecology 6: 1 99-202.

Fuller, S.J., Bull, C.M., Murray, K. and J Spencer. 2005. Clustering of related
individuals in a population of the Australian lizard, Egemia frerei. Molecular Ecology
14:1207-1213.

Gilchrist, H.G. and G.J. Robertson. 2000. Observations of marine birds and mammals
wintering at polynyas and ice edges in the Belcher Islands, Nunavut, Canada. Arctic
53:61-68.

Gompper, M.E., Gittleman, J .L. and R.K. Wayne. 1997. Genetic relatedness, coalitions
and social behaviour of white-nosed coatis, Nasua narica. Animal Behaviour 53:781-
797.

Goodnight, K.F. and DC. Queller. 1999. Computer software for performing likelihood
tests of pedigree relationship using genetic markers. Molecular Ecology. 8: 1231-1234.

Gorman, ML. and H. Milne. 1972. Creche behaviour in the Common Eider. Omis Scand.
3:21-5.

46

Goudie, K.I., Robertson, G.J. and A. Reed. 2000. Common Eider (Somateria
mollissima) In The Birds of North America, No 546 (A. Poole and F.Gill, eds). The
Birds of North America, Inc., Philadelphia, PA.

Gould, LL. and F. Heppner. 1974. The vee formation of Canada Geese. Auk 91 :494-
506.

Griffin, A.S. and SA. West. 2002. Kin selection: fact and fiction. Trends in Ecology and
Evolution 17(1):15-21.

Griffin, AS. and S.A.Wcst. 2003. Kin discrimination and the benefit of helping in
cooperatively breeding vertebrates. Science 203:634-636.

Haas, CC. and D. Valenzuela. 2002. Anti-predator benefits of group living in white-
nosed coatis (Nasua narica). Behav. Ecol. and Sociobiol. 51:570-578.

Hamilton, W.D. 1964 The Genetical Evolution of Social Behavior 1. J. Theoret. Biol.
7:1-16.

Hario, M., Hollmen, T.E., Morelli, TL. and KT. Scribner. 2002. Effects of mate removal
on the fecundity of common cider Somateria mollisima females.

Hawkins, RE. and W.D. Klimstra. 1970. A preliminary study of the social organization
of white-tailed deer. Journal of Wildlife Management 34:407-419.

Hoglund, J .and Sheldon, BC. 1998. The cost of reproduction and sexual selection.
Oikos 83: 478-483.

Holekamp, K.E., Cooper, S.M., Katona, C.I., Berry, N.A., Frank, LG, and L. Smale.
1997. Patterns of association among female spotted hyenas (Crocuta crocuta). J.
Mammology 78(1):55-64.

Kilpi, M. and K. Lindstrom. 1997. Habitat-specific clutch size and cost of incubation in
common eiders, Somateria mollisima. Oecologia] 11:297-301.

Kilpi, M., Ost, M., Lindstrom, K and H. Rita. 2001. Female characteristics and parental
care mode in the creching system of eiders, Somateria mollissima. Animal Behaviour
62:527-534.

Kimwele, ON and J .A. Graves. 2003. A molecular genetic analysis of the communal
nesting of the ostrich (Struthio camelus). Molecular Ecology 12:229-236.

Komdeur, J. and G.J. Hatchwell. 1999. Kin recognition: function and mechanism in avian
societies. Trends in Ecology and Evolution 14:237-241.

47

Korschgen, CE. 1977. Breeding stress of female eiders in Maine. J. Wildl. Manage.
41(3):360-373.

Lengyel, S. 2002. Adoption of chicks by the Pied Avocet. Waterbirds 25(1):109-1 l4.
Maak, S., Wimmers, K., Weigend, S. and K. Ncumanns. 2003. Isolation and
characterization of 18 microsatellites in the Peking duck (Anas platyrhynchos) and their

application in other waterfowl species. Molecular Ecology Notes 2: 224-227.

Matocq, MD. and EA. Lacey. 2004 Philopatry, kin clusters and genetic relatedness in a
population of woodrats (Neotoma macrotis). Behavioral Ecology 15(4):647-653.

Maynard-Smith, J. and GR. Price. 1973. The logic of animal conflict. Nature 246: 1 5-18.

Milne, H. 1976. Body weights and carcass composition of the Common Eider. Wildfowl
27:115-122.

Munro and Bedard 1977a. Creche behavior in the Common Eider. The Auk 94:759-771.

Munro and Bedard 1977b. Gull predation and creching behaviour in the Common Eider.
J. Anim. Ecol.46:799-810.

Milonoff, M., Poysa, H., Runko, P., V. Ruusila. 2004. Brood rearing costs affect future
reproduction in the precocial common goldeneye Bucephala clangula. Journal of Avian
Biology 35(4):344-351.

Moreno, J., Barbosa, A., Potti, J. and S. Merino. 1997. The effects of hatching date and
parental quality on chick grth and creching age in the chinstrap penguin (Pygoscelis
Antarctica): A field experiment. The Auk 114(1):47-54.

Nei, M. 1987. Molecular Evolutionary Genetics. Columbia University Press, New York.

Osorio-Beristain, M an dH. Drummond. 1993. natal dispersal and deferred breeding in
the blue-footed booby. Auk 110:234-239.

Ost, M. 1999. Within-season and between-year variation in the structure of common
cider broods. The Condor 101: 598-606.

Ost, M. and M. Kilpi. 2000. Eider females and broods from neighboring colonies use
segregated local feeding areas. Waterbirds 23(1):24-32.

Ost, M., Mantila, L. and M. Kilpi. 2002. Shared care provides time-budgeting advantages
for female eiders. Animal Behaviour 64:223-231.

Ost, M. Ydenberg, R., Kilpi, M. and K. Lindstrom. 2003. Condition and coalition
formation by brood-rearing common cider females. Behavioral Ecology 14(3):311-317.

48

Owen, M. 1980. Wild geese of the world. B.T. Batsford Ltd. London.

Patterson, I.J, Gilboa, A. and DJ. Tozer. 1982. Rearing other peoples young;Brood —
mixing in the shelduck Tadoma tadoma. Animal Behaviour 30: 199-202.

Parker, H. and H. Holm. 1990. Patterns of nutrient and energy expenditure in female
common eiders nesting in the high arctic. The Auk 107(4):660-668.

Paulus, KB. and Tiedemann. 2003. Ten polymorphic autosomal microsatellite loci for
the Eider duck Somateria mollissima and their cross-species applicability among
waterfowl species (Anatidae). Molecular Ecology Notes 3:250-252.

Pearce, J.M, Fields, R.L. and KT. Scribner. 1997. Nest materials as a source of genetic
data for avian ecological studies. J. Field Omith. 68(3):471-481.

Pope, TR. 2000. Reproductive success increased with degree of kinship in cooperative
coalition of female red howler monkeys (Alouatta seniculus). Behav. Ecol. Sociobiol.
48:253-267.

Prevett, J .P. and CD. MacInnes. 1980. Family and other social groups in snow geese.
Wildlife Monographs 4-46.

Raveling, D.G. 1969. Social classes of the Canada Geese in winter. I . Wildlife
Management 33:304-318.

Raveling, D.G. 1979. Traditional use of migration and winter roost sites by Canada
Geese. J. Wildl. Manage. 43(1):229-235.

Ratnayeke, S., Tuskan, GA. and MR. Pelton. 2002. Genetic relatedness and female
spatial organization in a solitary carnivore, the raccoon, Procyon lotor. Molecular
Ecology 11:1115-1124.

Raymond, M. and F. Rousset. 1995. GENEPOP (Version 1.2): Population genetics
software for exact tests and ecumenicism. J. Heredity 86:248-249.

Reed, A. 1975. Migration, homing and mortality of breeding female eiders Somateria
mollissima dresseri of the St. Lawrence estuary, Quebec. Omis Scand. 6(1):41-47.

Regehr, H.M., Smith, C .M., Arquilla, B. and F. Cooke. 2001. Post-fledgling broods of
migratory harlequin ducks accompany females to wintering areas. The Condor 103:408-
412.

Reynolds, J .D., Goodwin, NE. and RP. Freckleton. 2002. Evolutionary transitions in
parental care and live bearing in vertebrates. Phil. Trans. R. Soc. Lond. B 357:269-281.

49

Rice, W.R. 1989. Analyzing tables of statistical tests. Evolution 43:223-225.

Savard, J.P.L., Reed, A. and L. Lesage. 1989. Brood amalgamation in Surf Scoters
Melanitta perspicillata and other Mergini. Wildfowl 49: 129-138.

Schjorring, S. 2001. Ecologically determined natal philopatry within a colony of great
cormorants. Behavioral Ecology 12:287-294.

Schmutz, J .K., Robertson, R.J. and F. Cooke. 1982. Female sociality in the common cider
duck during brood rearing. Can. J. Zool. 60:3326-3331.

Schmutz, J.K., Robertson, R.J. and F. Cooke. 1983. Colonial nesting of the Hudson Bay
cider duck. Can. J. Zool. 61 :2424-2433.

Schoech, S.J., Mumme, R.L. and J .C. Wingfield. 1996. Prolactin and helping behaviour

in the cooperatively breeding Florida Sccrub-j ay, Aphclocoma c-cocrulescens. Animal
thaviour 52:445-456.

Scott, D.K. 1980. Functional aspects of prolonged parental care in Bewick’s swans.
Animal Behaviour 28(30):938-952.

Silk, J .B., Alberts, SC. and J. Altrnann. 2003. Social bonds of female baboons enhance
infant survival. Science 302: 1231-1234.

Stcarns, SC. 1976. Life-history tactics: A review of the ideas. The Quart. Rev.
Biol.51(1):3-47.

Sterk, E.H.M., Watts, DP. and GP. van Schaik. 1997. The evolution of female social
relationships in nonhuman primates. Behav. Ecol. Sociobiol.41:291-309.

Swensson, E. and Sheldon, BC. 1998. The social context of life history evolution. 1998.
Oikos 83:466-477.

Swennen, C. 1989. Gull predation upon Eider somateria mollissima ducklings:
destruction or elimination of the unfit? Ardca 77:21-45.

Queller, DC. 1992. A general model for kin selection. Evolution 46(2):376-3 80.

Van der Jeugd, J .P., van der Vcen,, LG. and K. Larsson. 2002. Kin clustering in bamacle
geese: familiarity or phenotype matching? Behavioral Ecology 13(6):786-790.

Wakeley, J .S. and H.L. Mcndall. 1976. Migrational homing and survival of adult female
eiders in Maine. J. Wildl. Manage. 40(1): 15-21.

dc Waal, REM. and PL. Tyack. 2003. Animal Social Complexity. Harvard University
Press, Cambridge, MA.

50

Warhurst, RA. and TA. Bookhout. 1983. Effect of gang brooding on survival of Canada
goose goslings. J. Wildl. Manage. 47(4): 1983.

Warren, S.M. , Fox, A.D., and P. O’Sullivan. 1993. Extended parent-offspring
relationships in Greenland white-fronted geese (Anser albifrons). Auk 110:145-148.

Whitehead, H. 1996. Babysitting, dive synchrony and indication of alloparental care in
sperm whales. Behav. Ecol. Sociobiol. 38:237-244.

Weller, M.W. 1957. An automatic nest trap for waterfowl. J. Wildl. Manage. 21 :456-
458.

Wcstneat, DP and I.R.K. Stewart. 2003. Extra-pair paternity in birds: causes, correlates
and conflict. Annu. Rev. Ecol. Evol. Syst.34:365-96.

Woolfenden, GE. 1976. Cooperative breeding in American birds. In: Proc. 16th Int. Om.
Congr. (Ed by H.J. Frith and J .H. Calaby). Australian Academy of Science.

51

   

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