Do MaleBreeding Displays Functionto AttractMatesor Defend
Territories?The ExplanatoryRole of Mateand Site Fidelity
RICHARD B. LANCTOT1, BRETT K. SANDERCOCK2'4AND BART KEMPENAERS3'5
'Alaska Biological Science Center, U.S. Geological Survey
1011 East Tudor Road, Anchorage, Alaska 99503, USA
Internet: richard_lanctot@usgs.gov
2Department of Biological Sciences, Simon Fraser University
Burnaby, British Columbia V5A 1S6, Canada
3AustrianAcademy of Sciences, Konrad Lorenz-Institute for Comparative Ethology (KLIVV)
Savoyenstrasse la, A-1160 Vienna, Austria
4Present Address: Centre for Applied Conservation Biology, 3rd Floor, Forest Sciences Centre
University of British Columbia, 3004-2424 Main Mall, Vancouver, BC V6T 1Z4, Canada
5Present Address: Research Center for Ornithology of the Max Planck Society
P.O. Box 1564, D-82305 Starnberg (Seewiesen), Germany
Abstract.-Many shorebirds show elaborate breeding displays that include aerial flights and ground displays accompanied by song. The mate attraction hypothesis suggests that breeding displays function to attract mates and
maintain pair bonds, whereas the territory defense hypothesis suggests breeding displays function in defining and
defending nesting and feeding territories. We tested these hypotheses in the Western Sandpiper (Calidrismauri)by
contrasting the duration and level of male breeding displays among pairs that differed in their mate and site fidelity.
As predicted by the mate attraction hypothesis, males performed the highest number of song sequences during pair
formation, and males paired with their mate of a prior year sang less than males paired to new mates. Further, sitefaithful males mated to a new but experienced mate displayed significantly more than remated males or males new
to the area. This suggests a male's prior familiarity with an area and his neighbors does not lessen his display rate as
was predicted under the territory defense hypothesis. Limited support for the territory defense hypothesis came
from observations of males performing breeding displays with neighboring males along nest territory boundaries.
This behavior was short-lived, however, as males abandoned nesting areas after pair-formation and used adjacent or
disjointed feeding areas during egg-laying and incubation. Male aggression (i.e., aerial and ground chases), as opposed to breeding displays, appeared to be the principal means of maintaining territory boundaries. Indeed, the
rate at which males chased other males remained fairly constant and high throughout the breeding season. Male
chasing behavior may also serve as a paternity guard to protect against extra-pair copulations. Our study also found
that a female's prior breeding experience in an area correlated with a reduced display rate by her mate, particularly
if that mate was new to the area. This indicates female characteristics may not only drive nest initiation, as has been
shown in other studies, but are important in determining the duration and extent of male display. Received:7February 2000, accepted10 March2000.
Key words.-Breeding displays, Calidrismauri,mate attraction, mate guarding, territory defense, song, Western
Sandpiper.
Waterbirds 23(2): 155-164, 2000
Shorebirds exhibit some of the most
elaborate breeding displays of any avian
group. In monogamous shorebirds, breeding displays frequently include elaborate
aerial flights and ground displays that are
commonly accompanied by song (Parmelee
et al. 1968; Heidemann and Oring 1976; Sordahl 1979; Miller 1979; Byrkjedal et al. 1989;
Byrkjedal 1990). Such displays are typically
performed by males and are thought to function primarily in mate attraction and pair
bonding (Holmes 1973; Miller 1979; Blom-
qvist et al. 1997). We call this the "mate attraction" hypothesis. Support for this
hypothesis comes from studies that indicate
recently paired male shorebirds show reduced levels of breeding displays relative to
unpaired males (Miller 1979; Whitfield and
Brade 1991). This decrease in display frequency may be due to males diverting their
energies to mate-guarding to prevent females from copulating with extra-pair males
(Birkhead and Moller 1992). Breeding displays may also function in defining and de-
155
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156
WATERBIRDS
fending territories;which we termed the
"territorydefense"hypothesis (describedin
Armstrong1973). Under this scenario, declines in displayrate maybe associatedwith
male establishmentof a territory.Maleswho
have successfullyestablisheda territorymay
be able to advertiseless frequently(Holmes
1973;Whitfieldand Brade 1991;Pierce and
Lifjeld1998). It is also possiblethat male display has a 'dual function', helping males to
attractfemales and defend their territories
(Catchpoleand Slater1995).
Determining the relativeimportance of
the above two hypotheses is difficult given
that mate attractionand territoryestablishment occur simultaneously(Table 1). Some
insight can be gained, however,by comparing the rate and duration of breeding displaysperformedby malesreunitedwiththeir
mate of a previousyear to males paired to a
new female. Males exhibiting mate fidelity
may displayat a lower level relativeto males
pairedwith an unfamiliarfemale if breeding
displaysfunction primarilyin mate attraction. This assumesthatfemalespairedto previous mates should require less information
regarding male and/or territoryquality.If
displaysfunction to provide such information, then males are likely to reduce display
intensityto save energy.It also assumesthat
females provide males with honest signals
that theyarewillingor likelyto matewith the
Table 1. Evidence that suggests breeding displays function in mate attraction or territory defense in monogamous
shorebirds. References for each item are identified by capital letters within parentheses. Instances where our study
supports, does not support, or does not test a line of evidence is indicated with an "+", "-", and "na", respectively.
I. Evidence for Mate Attraction Hypothesis
A. Display Phenology
1. Male display declines shortly after pair-bonds are formed or when incubation starts. (A, C, F, H, I,
J, K, P) +
2. Males perform the most displays during pair formation. (B, E, I) +
3. Males begin displaying again if his first nest is lost or his mate abandons him. (K) na
B. Male Characteristics
1. Paired males display less than unpaired males. (E, F, M) na
2. Remated males display less than experienced or new males paired to new mates. (J, L) +
C. Context of Display
1. Males display toward or with potential mates. (F) +
2. Displays are given only by males. (E, I, K, P) +
3. Male display does not induce neighboring males to display. (E) 4. Males display over large areas that overlap other male areas. (B,J) +
5. Males ignore other males displaying on territory once clutch is completed. (J, K, M, O) +
II. Evidence for Territory Defense Hypothesis
A. Display Phenology
1. Males display into incubation and/or brood-rearing. (D, E) B. Male Characteristics
1. Males continue to display after forming pair bonds. (D, E) +
2. Males familiar with their territory display less than males unfamiliar with their territory. + if with
prior mate
C. Context of Display
1. Males display toward conspecific neighbor males. (C, F) +
2. Displays are given by males and females. (I) 3. Males display with one or more other males. (D, P) +
4. Male display restricted to distinct areas that do not overlap across males. (A, N, P) 5. New males takeover vacated male areas when experimentally removed. (G) na
A = Ashkenazie and Safriel (1979), B = Blomqvist et al. (1997), C = Brown (1962), D = Byrkjedal (1990), E = Byrkjedal et al. (1989), F = Cairns (1982), G = Holmes (1970), H = Holmes (1971), I = Holmes (1973),J =Jehl (1973),
K = Miller (1979), L = Nethersole-Thompson (1951), M = Parmelee (1970), N = Pitelka et al. (1974), O = Tuck
(1972), P = Whitfield and Brade (1991).
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SANDPIPERBREEDINGDISPLAYFUNCTION
male in question. A decrease in display rate
with faithfulness to a mate is unlikely, however, if male breeding displays function primarily for territory defense. In a similar way, a
male's experience in a particular nesting
area may reduce the extent and duration of
his breeding displays. Here an "experienced"
male's greater familiaritywith an area and his
surrounding neighbors may make his territory easier to defend or less likely to be invaded
(the "dear-enemy" effect, see Fisher 1954;
Falls 1982; Ydenberg et al. 1988; Godard
1991, 1993). This relationship may not hold,
however, if male breeding displays function
primarily in mate attraction. Little is known
about how a female's familiarity with an area
will influence her mate's display rate.
The proximate effects of mate and site
fidelity on the rate and duration of breeding
display has rarely been quantified in shorebirds. Most researchers have simply related
male displaysto breeding chronology or male
pairing status, and have not considered the
potential explanatory effects of mate and site
fidelity (Heidelman and Oring 1976; Miller
1979; Byrkjedal et al. 1989; Blomqvist et al.
1997). Two exceptions include studies byJehl
(1970, 1973) on Stilt Sandpipers (Calidrishimantopus)and Nethersole-Thompson (1951)
on Common Greenshanks (Tringanebularia).
They suggested that territorial and courtship
behavior was reduced in old pairs (i.e., remated from a prior year) relative to new pairs, but
provided little quantitative support. Western
Sandpipers (Calidrismauri) are an excellent
species to investigate these relationships. After undertaking a long distance spring migration from Equatorial regions to Alaska
(Butler et al. 1987), males arrive on the breeding grounds before females and immediately
begin performing elaborate aerial displays accompanied by vocalizations (Holmes 1973;
Wilson 1994). Intra-male chases and fights
are common and may continue until young
hatch (Holmes 1973). Local survival (
=0.57) of adult Western Sandpipers (Sandercock et al., MS) is relatively low compared to
most other shorebirds for which values are
available (Sandercock and Gratto-Trevor
1997). This may require many adults to pair
with new mates from year-to-yearand opens
157
territories to yearling or inexperienced males
(Holmes 1971; Sandercock et al. MS). Thus
there is the potential for breeding displays to
function in both mate attraction and territory establishment.
In this study, we used a marked population of Western Sandpipers to document how
mate and site fidelity affected the duration
and frequency of male breeding displays (i.e.,
singing and chasing rates). We used these results to support or negate the mate attraction
and territory defense hypotheses for why
males perform breeding displays. We also
measured male mate-guarding behaviors
throughout the breeding season to provide a
better understanding of the role of intra-male
aggression as a paternity guard. Because the
relatively synchronous breeding and low
number of renesting attempts recorded for
this species provide little opportunity for obtaining additional matings (Sandercock et al.
1999), we predicted we would see little variation in mate guarding behavior amongst
males differing in mate fidelity.
METHODS
We studied Western Sandpipers on a four km2site located 21 km E of Nome, Alaska (64020'N, 164056'W)
during May-June 1996. The study site is located along
the Bering Sea coast and contains shallow tundra ponds
interspersed with low dry ridges. The breeding ecology
of this population had been studied during 1993-1995
and consequently many individuals returning in 1996
were already uniquely marked with color bands. Nesting
densities were relatively high at the study site, with 16.5
nests km2 observed in 1996.
Nests were located by observing individuals visit
their nest sites during behavioral observations, by opportunistically flushing parents off their nests or by
watching birds return to their nests. Locations of nests
were plotted on aerial photographs (scales: 1:1250 to
1:1600). Nests with less than 4 eggs (modal clutch size)
were revisited daily until clutch completion. If the nest
contained 4 eggs when discovered, we used the buoyancy and angle at which eggs floated to estimate hatching
date (Sandercock 1998a). Nests were subsequently visited every 6-7 days during incubation and daily near expected hatching date. Date of clutch initiation ("laying
date") was back-calculated by (1) the observed egg-laying schedule (0.8 eggs dayl), (2) date of hatching (assuming 21 day incubation period) or (3) stage of
incubation, based on egg flotation (for nests that failed
to hatch). Adults were captured with walk-in traps
placed over their nests and sexed by culmen length
(males < 24.2 mm, females >24.8 mm; Page and Fearis
1971; Cartar 1984; Sandercock 1998b). This method
had ca. 95% accuracy for individual birds and 100% for
pairs. We aged individuals by the coloration of the inner
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158
WATERBIRDS
tertial and wing coverts. Yearlings were distinguished by
their buff or chestnut edges, whereas adults had white
edges (Prater et al. 1977; Sandercock 1998b).
Behavioral Observations
We conducted behavioral observations on banded
males and females from their arrival on the breeding
grounds until shortly after clutch completion (11 to 26
May). Observations were then categorized into pre-fertile, fertile and post-fertile periods, based on clutch initiation dates. We assumed females were fertile from days -5
to +2 when day 0 was equal to the date when the first egg
was laid. It is very likely that females can store sperm for a
longer time and are thus already fertile before day -5.
However, the average number of days (? SE) from the
first observation of an adult to the first egg was relatively
short (males: 6.2 ? 0.7, N = 30; females: 4.6 + 0.6, N = 25),
so for practical reasons we defined the pre-fertile period
as starting before day -5. Behavioral observations were
usually terminated shortly after egg-laying (i.e., 4 days
into incubation) because only one adult was visible (the
other was incubating) and this bird primarilyfed. Useable
focal observations totaled 44 hrs on 33 different pairs. Behavioral data were available on 14, 24, and 9 pairs during
the pre-fertile, fertile and post-fertile periods, respectively. Each pair was observed for 47 ? 6.6 min (mean ? SE)
during the pre-fertile, 72 ? 9.6 min during the fertile, and
26 ? 4.3 min during the post-fertile period.
Observations were conducted on a daily basis by
three people who dispersed throughout the study area.
Focal observations were started whenever a marked individual was detected, and each pair was followed for 30
min if possible. During each focal observation, we recorded male vocalizations, male-male aggression, and
distance between males and females. As a measurement
of male breeding display rate, we quantified the number
of "trill"songs per minute (Wilson 1994) and the number of song sequences (defined as a series of consecutive
trill songs without interruption) per minute. Songs are
performed during display flights and on the ground
and are frequently used during aerial chases (see description of display flights in Brown 1962; Holmes
1973). Because both the number of trills min-' and the
number of song sequences min-' were highly correlated
during the fertile period (Spearman r24= 0.91, P <
0.001), we used the latter variable in further analyses.
The number of song sequences min-' was converted to
song sequences hr' for presentation. As an index of
male-male aggression, we recorded the number of aerial and ground chases made by the focal male towards intruding males. The intensity of mate guarding was
determined by recording the distances between males
and females on a continuous basis to the nearest meter.
We then calculated the proportion of the total observation time during which males were less than or equal to
5 meters from their mate as a mate guarding variable.
Efforts to record other measures of mate guarding, such
as whether males respond more often to female movements during the fertile stage than during non-fertile
stages, proved unsuccessful because of low sample sizes.
Statistical Analyses
For all analyses we used the pair as our sample unit.
Focal observations where males were followed for less
than 5 min were excluded from all analyses. For pairs
that were observed more than once during a day, we
summed observation time and the recorded variables.
For each pair, we then averaged the observations during
different days within pre-fertile, fertile, and post-fertile
stages and used these averages in further analyses. By
summarizing the data this way, each day of each stage
was given equal weight. Not all pairs were observed in all
three breeding stages, and we could not perform an
analysis of variance (repeated or single factor) to evaluate changes in male behavior through the season. Consequently we performed paired comparisons of male
behavior with those pairs observed in more than one
breeding stage.
We contrasted pairs which differed in pair status to
evaluate the effects of mate and site fidelity on male
breeding behavior. These analyses were limited to the
fertile period where our sample sizes were sufficiently
high. We characterized males and females based on
whether (1) they had bred with the same mate as in
1995 (i.e., "remated"), (2) they had bred at our study
site before, and (3) their mate had bred at our study site
before. Males and females who were site faithful were
considered "experienced" in the study area, whereas
adults first captured in 1996 and yearlings were considered "inexperienced". Adult birds first captured in 1996
represented 27.3% of females and 18.2% of all males,
whereas yearlings represented 12.1% of females and
3.0% of males. The assumption that these birds were
"inexperienced" at our study site seems reasonable, given our intensive banding efforts between 1993 and
1996, and the high recapture rates between years
(>80%). Recapture (i.e., resighting) rates were different
than local survival rates (see above) because the former
depends on the probability of breeding, the probability
of detecting a nest, and the probability of capturing the
bird, whereas the latter depends on true survival and local site-fidelity (Sandercock et al. MS).
We used SYSTAT7.0 (1997) to conduct analyses. We
relied on non-parametric statistics for most analyses because data were non-normally distributed and sample
sizes were small. Sample sizes became limited in this
study because behavioral observations were restricted to
banded birds whose nest initiation date could be determined, and because many analyses used only a portion
of the breeding population (e.g., a particular pair and
site-faithful group). Tests were two-tailed and considered to be significant at the 0.05 level. Data are presented as medians and ranges unless otherwise noted.
RESULTS
The first Western Sandpiper male performed aerial breeding displays on 10 May
1996 and within two days there were numerous males displaying. Females initiated nests
almost immediately (median laying dale and
range were 21 May, 13 May-3June; Sandercock et al. MS). The first remated pair was recorded on 11 May. Males performed aerial
displays accompanied by vocalizations over a
large area but their energies were focused
over tundra heath habitat in which their
nests were subsequently found. Displays
were occasionally performed with one or two
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159
SANDPIPERBREEDINGDISPLAYFUNCTION
other males simultaneously, but not in a duetting fashion. Aside from their nesting territory, pairs also had either adjacent or
separate feeding areas along wetland edges
that they used during and after egg-laying.
Males rarely sang over feeding territories,
and these areas typically did not overlap
among pairs. After clutches were completed,
it was not uncommon for new, late-arriving
males to display over nesting habitat in
which females had previously initiated nests.
40
30
S2010
0
N= 14
N=24
Pre
Fertile
N=9
Post
Breeding
Stage
Mate Fidelity Between and Within Seasons
Of 48 banded birds resighted in 1996,
only 18 (37.5%) birds paired with their mate
from the previous year. Nine (69%) of 13
pairs, where both members were observed
on the study area in 1996, remated (i.e., 4
pairs divorced). This was similar to the mate
fidelity rates in 1994-1995 (65.2% N = 23;
Sandercock et al. MS). We observed three occasions where adult females, and once where
an adult male, nested twice within the same
year after the first nest failed. Two of the
three females had nested on the study area
in previous years. They first paired with their
mate from 1995, and then one mated with
another experienced male and the other
mated with a new male. The third female was
new and sequentially mated with two males
that had previously bred on the study area.
The single male that renested had bred on
the study area in a previous year, but we
could not determine whether he changed
mates because his first mate was unbanded.
exhibited
Figure 1. The number of song sequences
hr-'
by male Western Sandpipers during the pre-fertile, fertile and post-fertile breeding stages. See text for definition of breeding stages. Sample sizes are listed above
the x-axis. Box plots include the median (solid line),
25th and 75th quartile (box outline), and 5th and 95th
quartile (bars with caps).
stages (fertile: 12.5, 3.2-16.7; post-fertile: 2.7,
0-13.1, N = 8; U= 55, P= 0.02). Observations
of male chases revealed little to no change
between six males observed in the pre-fertile
and fertile stages (pre-fertile: 2.2, 0-28.0,
chases hr'; fertile: 1.4, 0-24.1; U = 19, P =
0.87), and eight males observed in the fertile
and post-fertile stages (fertile: 7.9, 0-16.0;
post-fertile: 1.7, 0-21.1; U = 45, P= 0.17).
Male chases during the pre-fertile stage were
directed at other Western Sandpipers that
frequented the nesting territory of a pair.
Chases during the fertile and post-fertile
stages, in contrast, were directed at both conspecifics and heterospecifics and were concentrated at the feeding territory of a pair.
Other species that were chased included
Semipalmated Sandpipers (C. pusilla), DunMale-Male
Breeding Displays,
Aggression,
lin (C. alpina), Red-necked Phalaropes
and Mate Guarding
(Phalaropuslobatus),and Lapland Longspurs
Male vocalization rates were highest at (Calcariuslapponicus).Males also chased oththe beginning of the breeding season and er male Western Sandpipers when they atappeared to decline thereafter (Fig. 1). Pair- tempted to copulate with their mate. These
wise analyses, however, limited to males ob- attempted extra-pair copulations occurred
served in both the pre-fertile and fertile stag- primarily at feeding territories. Females also
es indicated no significant decline in song chased away intruding male Western Sandrate (median and range of song sequences pipers from feeding areas on eight occahr'; pre-fertile: 13.1, 4.9-32.7, fertile: 7.3, 5.0- sions. Males spent about 70-80% of their
12.4, N = 6, Mann-Whitney U test statistic = time within 5 m of their females during the
28, P= 0.11). There was a significant decline, pre-fertile and fertile stages (N = 9 and 23,
however, between the fertile and post-fertile respectively), and 30% during the post-ferThis content downloaded from 129.130.115.17 on Fri, 30 Oct 2015 19:31:33 UTC
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WATERBIRDS
160
tile stage (N = 2). Sample sizes were too small
to test for changes among breeding stages
for this parameter.
Only six copulations were observed during the study. These occurred between 14
and 21 May at -9, -2, -1 and +2 days (breeding
day for two of the six copulations was not
known) of the female's egg-laying cycle. An
additional five attempted copulations were
observed between 14 and 23 May (on days -6,
-6, -4, -1, and +3). In all the attempted copulation cases, the female moved awayfrom the
advancing male. Only two attempted extrapair copulations were observed in this study
on the 17 and 22 May (on day +7 for one
female). On both attempts, the female's
mate chased the intruder away. Copulations
and attempted copulations were observed
between 1136 and 2218 h, but were most
common in the afternoon (median = 1359 h,
N= 11).
Pair Status Effects on Singing, Chasing, and
Mate-Guarding
Males who remated with their mate of
1995 sang significantly less than did males
paired with a new mate (whether experienced or not), having roughly half the median song sequences hW (Table 2, P = 0.04).
Pairs where both the male and female were
experienced, but were not former mates, exhibited the highest song rate of any pair status group. This male-female group sang
significantly more than pairs in which only
the female was experienced (P = 0.01) and
nearly significantly more than pairs in which
only the male was experienced (P = 0.06,
Table 2). There were no differences between
any of the pair status groups in chase rate or
mate guarding (Table 2). Given the significant differences in song rate exhibited by
males among our treatment groups, we con-
Table 2. Statistical comparisons of male song sequence rate, chase rate, and mate-guarding by male Western Sandpipers with different mate and site fidelity during the fertile stage (-5 to +2 where day 0 is equal to the date when
the first egg was laid). Birds were considered "experienced in area" if they had bred on the study area prior to 1996.
Similarly birds were considered "new to area" when they had not been captured and banded in prior years. This
included yearlings (8.3% of all males and 4.1% of all females) and a small number of adults (20% of all males and
females, respectively). Bolded areas indicated significant differences with an alpha level of 0.05.
Experienced male
paired with:
Variable
Male song sequences hr-i
Median
Range
N
Experienced female paired
with different male
from 1995 who was:
same mate
as 1995
new
mate
experienced
in area'
new
to area
experienced
in area'
new
to area
5.8
2.4-14.0
8
12
3.3-20.7
15
16.3
15.7-20.7
4
12.3
3.3-17.4
6
16.3
15.7-20.7
4
8.1
4.9-12.0
5
"U = 91.5, P = 0.04"
Mann-Whitney
Experienced male paired
with different female
from 1995 who was:
"U = 21, P = 0.06"
"U = 20, P = 0.01"
Male chases hr-i
5
0-16.0
8
Median
Range
N
"U = 58, P = 0.90"
Mann-Whitney
Percentage of time with mates
Median
Range
N
Mann-Whitney
4.7
0-23.6
15
81
10-98
8
70
40-100
14
"U = 47, P = 0.54"
6.4
0-20.7
4
8.4
0-23.6
6
"U = 9.5, P = 0.59"
64
42-92
4
64
42-92
5
"U = 11, P = 0.81"
6.4
0-20.7
4
2
0-4.7
5
"U = 15, P = 0.21"
64
42-92
4
73
60-100
5
"U = 8, P = 0.62"
'These two columns represent the same group of males. These data are presented twice so that the role of male
and female breeding experience may be explored separately.
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SANDPIPERBREEDINGDISPLAYFUNCTION
ducted an a posterioricomparison between
remated pairs and pairs in which both the
male and female were experienced but not
previously paired to each other. This test indicated remated pairs sang significantly less
(U= 32, P= 0.007).
DISCUSSION
Function of Breeding Displays
The relationship between a male's conspicuous breeding displays and his territory
are poorly understood, especially among monogamous species, despite the efforts of researchers during the past several decades
(Miller 1979; Byrkjedal et al. 1989; Whitfield
and Brade 1991; Blomqvist et al. 1997). A review of the literature for shorebirds indicates
researchers rely on breeding display phenology, male characteristics, and the context of
the displays to determine whether breeding
displays function in mate attraction or territory defense (Table 1). Most of our data supported the mate attraction hypothesis. First,
male display was highest during pair formation and then declined significantly from the
fertile to post-fertile stages (Table 1, I, Al-2).
Second, males paired with their mate of a prior year performed fewer song sequences
than experienced or new males paired with
different mates (Table 1, I, B2). Third, the
high singing rates of males with previous site
experience (unless they remated) suggests
that this experience does not reduce their
need to defend territories, as was predicted
under the territory defense hypothesis (Table 1, II, B2). Instead, the familiarity of a
male's mate with her breeding area seemed
more important in determining how much a
male sang (see below). Fourth, only males
performed breeding displays (Table 1, I, C2;
although this fact does not negate the territory defense hypothesis). The mate attraction
hypothesis also was supported by several other lines of evidence for which we had no
quantitative data. Anecdotal observations indicated male displays were not restricted to
their nesting areas but overlapped with
neighboring male nest sites (Table 1, I, C4).
Males also stopped displaying over their nest-
161
ing territories and began defending nearby
feeding territories from both conspecific and
heterospecific species once clutches were
completed. This allowed late-arriving males
to display over previously defended nesting
territories without retribution (Table 1, I,
C5). Males are unlikely to allow such intrusions under the territory defense hypothesis.
There was some evidence, however, that
suggested males used breeding displays in
territory defense. First, displays were frequently performed with neighboring males
along territory boundaries (Table 1, part II,
C1, 3). Brown (1962) also observed male
Western Sandpipers singing to one another
and suggested these songs might serve to repel intruders. Our data suggest males may
use other mechanisms besides singing to
maintain territories. For example, males performed aggressive behaviors, such as aerial
and ground chases, throughout the breeding season. This aggression consisted of
males chasing intruders from nesting territories during the pre-fertile stage, from feeding territories during the fertile and postfertile stage, and from their mates after attempted extra-pair copulations. Such aggression was directed at both conspecifics (male
and female) and heterospecifics. Holmes
(1973), studying Western Sandpipers on the
Kolomak River 350 km south of our study
area, did not dismiss the mate attraction hypothesis, but suggested that the decline in
breeding displays could as easily be explained by the establishment of territory
boundaries. This seems unlikely given that
nest territory boundaries were frequently
violated once a pair had completed laying.
Holmes also indicated declines in breeding
displays might occur as males moved to feeding territories and adults began incubating
clutches. While we cannot refute this possibility, it also seems unlikely given the constant
rate of male chases observed throughout the
breeding season, which suggests that conflicts were not decreasing. Taken together,
our observations support primarily the mate
attraction hypothesis, with weaker support
for the territory defense hypotheses, as explanations for male breeding displays in
Western Sandpipers.
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WATERBIRDS
162
A Role for Female Site Experience
A female's prior breeding site experience
had a strong effect on the singing rate of a
male. This was particularly true when experienced females were paired with inexperienced males. It seems likely that the lower
song rates exhibited by these inexperienced
males are a direct result of when birds arrived
on the study area. Resighting data suggests
that experienced birds typically arrived earlier than inexperienced birds (R. Lanctot and
B. Sandercock, unpubl. data), and that experienced females typically laid earlier than inexperienced females (Sandercock et al.
1999). Should experienced females lose their
first nest and choose to renest with another
male (as did the three renesting females observed in 1996), then these late-arriving, inexperienced males may need to display very
little (or chase intruders) before females are
ready to pair and lay their eggs. An alternative explanation for the low rate of singing by
inexperienced males may be that they lack
the capability or have not learned the consequences of not displaying vigorously.
The high song and chase rates of experienced males paired to experienced females
may also be explained by arrivaltimes. Experienced adults generally arrived early in the
season when competition for sites and high
quality mates was high. Such a situation may
require intense male display and aggression
to successfully acquire a territory and mate.
Alternatively, the high levels of display may
be an artifact of the male trying to attract the
female to his territory while the female prefers to settle on her territory of a previous
year. Whatever the explanation, prior female
site experience appears to control not only
nest initiation (Sandercock et al. 1999), but
also to have a strong influence, whether direct or indirect, on the level of male display
and aggression that precedes it.
Benefits to Site and Mate Fidelity
Sandercock et al. (1999) found that only
female familiarity with a breeding area, not
mate fidelity or female age, significantly affected timing of laying. Nesting earlier may
benefit males by reducing their probability
of being cuckolded, as late-nesting females
have greater access to extra-pair copulations
via early nesting males on incubation breaks
and late-arriving males. Our data on mate
guarding and copulation behavior suggest,
however, that the risk of cuckoldry is low in
this population, despite the high breeding
density. Mate and site fidelity of the male and
female did not affect the percentage of time
males spent near females during the fertile
period, and females resisted extra-pair copulations and even chased conspecific males
away.Further, the low copulation rates in this
species suggest frequent copulation was not
used as a compensatory paternity guard
(Birkhead and Moller 1992), another indicator that extra-pair fertilizations are rare. Other studies on monogamous shorebirds also
documented consistent mate guarding levels
across breeding stages and low rates of extrapair copulations (Heg et al. 1993, Pierce and
Lifjeld 1998; Zharikov and Nol 2000).
Mate fidelity may also benefit males by allowing them to reduce the amount of energy
they invest in performing breeding displays.
Remated males had the lowest song sequence
rate relative to any other pair status group.
New males paired with experienced females
also sang less, and had the lowest chasing rate
of any group. Unfortunately, we could not
measure breeding display rates of inexperienced males paired to inexperienced females
(i.e., those in which both the male and female were new to the study area). These
males might be expected to use the most energy establishing territories among previously settled males and then competing with
these males to attract mates. Reducing energy needs may be particular important to male
shorebirds breeding at high latitudes because they must arrivewith sufficient reserves
to establish and defend nesting and feeding
territories, attract a mate, and then defend
this mate from other males-all at a time
when food is limited. Breeding displays may
thus act as honest signals of a male's quality
because of their high energetic costs and inefficient production (Reid 1987; Ryan 1988);
maintenance of such displays could then occur through the actions of female choice.
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SANDPIPERBREEDINGDISPLAYFUNCTION
Natural selection, in contrast, may lead to
lower breeding display levels, through direct
and indirect mechanisms which promote remating (Choudhury 1995; Ens et al. 1996).
This study illustrated the important role
mate and site fidelity can play in understanding the function of male breeding displays.
The majority of our data indicated male
breeding displays functioned primarily to
attract mates, with less evidence supporting
territory defense. Of particular note was how
female experience in a breeding area reduced the display rates of males, especially
if these males were new to the study area. Obviously other factors may influence male
breeding displays as well, including time of
day, weather (Miller 1979), territory characteristics, and the prospects of mate or site improvement (Ens et al. 1996). Future studies
would benefit from collecting detailed behavioral data over several years so that between-year comparisons of individual male
behavior under similar and different socioecological conditions can be conducted.
This would help remove many confounding
variables, such as differences in male and territory quality, unaccounted for when males
of different status are compared within years.
Alternatively, mate removal experiments or
experimental presentations of song (see e.g.,
Eriksson and Wallin 1986) may be useful for
clarifying the role of breeding displays in
mate attraction and territory defense.
ACKNOWLEDGMENTS
We thank L. Edwards and S. Hall for help in the
field. Erica Nol and Cheri Gratto-Trevor provided insightful comments that improved earlier versions of the
manuscript. The Sitnasauk Native Corporation permitted access to their lands to conduct this study. R. E. Gill,
Jr. (U.S. Geological Survey), R. Harris (National Park
Service), and Mark Webb (U.S. Fish and Wildlife Service) provided logistical support. The research was
funded by the Belgium Fund for Scientific Research,
the CWS/NSERC Research Chair in Wildlife Ecology,
the Konrad Lorenz Institute for Comparative Ethology,
an NSERC Operating Grant (to F. Cooke), Simon Fraser
University, and the U.S. Geological Survey (Alaska Biological Science Center).
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Do Male Breeding Displays Function to Attract Mates or Defend Territories? The Explanatory
Role of Mate and Site Fidelity
Author(s): Richard B. Lanctot, Brett K. Sandercock and Bart Kempenaers
Source: Waterbirds: The International Journal of Waterbird Biology, Vol. 23, No. 2 (2000), pp.
155-164
Published by: Waterbird Society
Stable URL: http://www.jstor.org/stable/4641137
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