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We studied two courtship displays of male peafowl (Pavo cristatus), focusing particularly on male orientation relative to the position of the sun. During the “wing-shaking” display, females were generally behind the displaying male, and male orientation with respect to the position of the sun was not significantly different from random. However, during the pre-copulatory “train-rattling” display, males were on average directed at about 45° to the right of the sun azimuth with the female positioned directly in front, suggesting that this behaviour is involved in the communication of a visual signal. A model presentation experiment confirmed that courting peacocks were more likely to perform the train-rattling display when the female was on the sunny side of their erect train, but more likely to perform wing-shaking behaviour when the female was on the shaded side of the male. This study underscores the importance of visual signalling in peafowl courtship, and we suggest that an angle of about 45° relative to the sun may allow males to enhance the appearance of their iridescent eyespot feathers.
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ORIGINAL PAPER
Peacocks orient their courtship displays towards the sun
Roslyn Dakin & Robert Montgomerie
Received: 17 October 2008 / Revised: 21 January 2009 / Accepted: 22 January 2009
#
Springer-Verlag 2009
Abstract We studied two courtship d isplays of male
peafowl ( Pavo cristatus), focusing particularly on male
orientation relative to the position of the sun. During the
wing-shaking display, females were generally behind
the displaying male, and male orientation with respect to
the position of the sun was not significantly different from
random. However, during the pre-copulatory train-rattling
display, males were on average directed at about 45° to the
right of the sun azimuth with the female positioned directly
in front, suggesting that this behaviour is involved in the
communication of a visual signal. A model presentation
experiment confirmed that courting peacocks were more
likely to perform the train-rattling display when the female
was on the sunny side of their erect train, but more likely to
perform wing-shaking behaviour when the female was on
the shaded side of the male. This study undersc ores the
importance of visual signalling in peafowl courtship, and
we suggest that an angle of about 45° relative to the sun
may allow males to enhance the appearance of their
iridescent eyespot feathers.
Keywords Peacock
.
Signal efficacy
.
Display
.
Courtship
Introduction
In many species, both the location and timing of courtship
displays appear to be selected for signal efficacy. For
example, it has been suggested that the almost ubiquitous
dawn chorus of birds is timed to minimize interference
from wind and other noise (Henwood and Fabric k 1979)
and thus maximize signal transmission distance and quality.
Similarly, several neotropical lekki ng birds (Rupicola
rupicola, Corapipo gutturalis, Lepidothrix serena) perform
courtship displays at times when the contrast of male
plumage against the visual background is maximized
(Endler and Théry 1996), and the vertical placement of
display arenas in several lekking manakins corresponds
with the locations predicted to maximize male plumage
contrast agains t the background (Heindl and Winkler 2003).
Moreover, the courtship and territorial dive displays made
by male Anna's hummingbirds (Calypte anna) are oriented
in the general direction of the sun such that the reflecting
value of the iridescent, rose-coloured gorget plumage is
maximized towards the target female or male (Hamilton
1965). To the best of our knowledge, this is the only
example of both the location and orientation of a display
influencing the efficacy of a signal.
In the present study, we examine the courtship displays
of free-ranging peacocks (Pavo cristatus ) in relation to both
the light environment and the relative positions of females
being courted. Peahens visit a number of males during each
breeding episode before copulating with one or (at most)
two of the males that they visited previously (Petrie et al.
1991, 1992). Most studies to date indicate that peahens base
their mate choices on some visible aspect of the elaborate
and colourful male upper-tail feathers (or train; Petri e et
al. 1991; Petrie and Halliday 1994; Loyau et al. 2005,
2007a), as Darwin (1871) surmised. Interestingly, however,
Behav Ecol Sociobiol
DOI 10.1007/s00265-009-0717-6
Communicated by I. Cuthill
Electronic supplementary material The online version of this article
(doi:10.1007/s00265-009-0717-6) contains supplementary material,
which is available to authorized users.
R. Dakin (*)
:
R. Montgomerie
Department of Biology, Queens University,
Kingston, ON K7L 3N6, Canada
e-mail: 2rd@queensu.ca
Takahashi et al. (2008) present data to suggest that male
train ornamentation, in general, and eyespots, in particular,
do not influence female choice and may be relicts of past
selection. The findings of Takahashi et al. ( 2008) have
recently been interpreted in the science press as indicating
that Darwin's theory of sexual selection might not work in
the case of the peacock's colourful tail (Anonymous 2008 ;
see also Morell 2008).
Peacocks strut around with trains erect in both the
presence and absence of females (Fig. 1; see also Video 1 in
the Electronic Supplementary Material (ESM)). When their
trains are erect, males occasionally perform a wing-
shaking display whether or not females ar e present,
shaking their wings up and down vigorously behind the
erect train, sometimes for 510 min at a time. In the
presence of females, males also perform a train-rattling
display for up to 6 min at a time, rapidly vibrating the
rectrices that support their train feathers in the upright
position, such that those feathers make a noise audible from
several metres away (also called shivering in Petrie et al.
(1992) and Takahashi et al. (2008)). The wing-shaking
display often precedes the train-rattling display when
females are present, and the train-rattling display always
precedes copulation, though the sequenc e of events during
courtship can be somewhat variable (Fig. 2 ).
Given the complexity of peacock displays and the
observation that peacocks do not necessarily orient their
erect trains towards a target female, our aims in this study
were twofold. First, we sought to describe the directionality
of peacock display behaviour and quantify the relative
positions of both the male and the target female being
courted during a courtship sequence. Second, we asked
whether the direction that a male faces during train displays
is related to the position of the sun, as one might expect if
male behaviour functions to display the iridescent colours
of the train plumage (see Loyau et al. 2007a ) effectively to
prospective mates.
We addressed these questions by observing males
courting females over the normal course of the breeding
season and by conducting an experiment involving the
presentation of a model female. The experiment allowed us
on lek
70%
off lek
30%
forage
rest
aggression
train up
23%
train down
77%
perch 27%
stand vigilant 57%
preen 7%
sit 9%
female(s) absent
24%
female(s) present
76%
wing-shake
35%
train up only
65%
wing-shake
51%
train-rattle
23%
train up only
26%
turn/walk 45%
stationary 55%
turn/walk 47%
stationary 53%
turn/walk 33%
stationary 67%
turn/walk 7%
stationary 93%
turn/walk 32%
stationary 68%
Fig. 1 Daily time budget for peacocks showing the average percent of
time males devoted to each activity at each level in the hierarchy.
Percentages during train up are averages calculated from the longest
display bouts recorded for each of 11 males at LAA and APZ in 2008
between 07:00 and 19:00 local times. Percentages during all other
activities (including train up versus train down) are averages
calculated from observations over a single day at LAA where we
sampled each of 17 males once per hour for 12 h (07:0019:00)
female presence
wing-shaking
train-rattling
1
2
3
4
5
6
7
8
9
10
11
0 5 10 15 20 25 30 35
time (minutes)
bout
male
Fig. 2 Sequence of events over the longest bout recorded from each
of 11 different males, based on point samples taken at 30-s intervals.
Note that wing-shaking and train-rattling displays sometimes stopped
briefly between point samples, even though they are illustrated here as
continuous
Behav Ecol Sociobiol
to control for the potential effect of female movement on
male orientation and to determine how the p atterns of male
display behaviour observed under normal conditions were
influenced by the positions of both the sun and the target
female.
Materials and methods
Study species
Peafowl are native to the Indian subcontinent but began to
be introduced to other parts of the world at least 12
centuries ago (Kannan and James 1998) and are now found
in both captive and feral populations in parks, farms, zoos
and estates worldwide. Almost all that is known about
peafowl comes from studies conducted in these populations
away from the ancestral habitats of these birds, but these
captive birds do exhibit behaviours similar to those of
free-ranging birds in their natural habit ats (Hillgarth 1984).
During the breedi ng season, sexually mature males
gather at leks comprising one to 11 males, with individual
males generally using the same display court throughout
the breeding season (Yasmin and Yahya 1996;R.Dakin,
personal observation). At our study sites, one to six males
occupied the leks we sampled, with a median lek size of
four males. Males displayed on their leks each day,
mostly from 08:00 to 10:00 and 16:0018:00 local times
(see also Petrie et al. 1991). On a lek, each male occupied
and defended a 23-m
2
display court where almost all
displays and copulations occurred. Courts within a lek
were 5-20 m apart, and all male s on a lek could easily see
one another.
In the presence of females, peacocks perform an
elaborate courtship ritual involving calls and the presenta-
tion of the visual train ornament (Video 1 in the ESM),
comprised of about 150 highly elongated upper-tail coverts,
each with a single multi-coloured, iridescent eyespot.
Darwin (1871) describe d the males strutting about, with
expanded and quivering tail-feathers and mentioned that
they also rattle their quills together. Petrie et al. (1992)
provided a more detailed description of the sequence of
events during courtship: when a female approaches a
displaying male, he turns away [from her] showing the
rear surface of his train and his orange primari es which are
moved vigorously up and down if the female follows the
male's turning movement , so that she appears in front of
him, he turns to face her head-on and shivers his train.
This sequence may be repeated a number of times, after which
the male will usually attempt to mount the female (Petrie et al.
1992; R. Dakin, personal observations; Video 1 in ESM). The
male is generally stationary during the train-rattling display
but may take a few steps towards the target female.
Field sites
We observed peafowl at the Assiniboine Park Zoo
(Manitoba, Canada; APZ, 50 ha) in May 2007, at the Los
Angeles Arboretum (California, USA; LAA, 50 ha) in
MarchApril 2008 and at the Bronx Zoo (New York, USA;
BZ, 100 ha) in May 2008. APZ has a population of
approximately 60 peafowl that range freely over the zoo's
parklands from April to October and are kept in large
indoor enclosures during the winter months. LAA and BZ
are each inhabited by feral populations of >100 peafowl
that range throughout the park grounds and surrounding
habitats year-round. Birds at all sites were observed on their
display courts during their respective peak lekking seasons:
March at LAA; MayJune at APZ and BZ.
Male display orientation
We studied the behaviour of 11 displaying peacocks during
the morning (07:00 12:00 local times) and late afternoon
(15:0019:00) at both APZ (five males in two leks) and
LAA (six males in four leks) on days when the sky was
clear enough for shadows to be visible on the ground and
thus when the position of t he sun could be clearly
discerned. For man y of the display bouts obser ved,
however, male display courts were in full shade such that
the sun was not directly visible and no shadows were cast
(see Results for details).
We identified males mainly by numbered leg bands or
unique morphological features, but in a few cases by the
location of a display court maintained by a particular male
peacocks almost always maintain a single display court
throughout the breeding season (unpublished data). We
observed individual males from 510 m away, as this
appeared not to interfere in any way with their behaviour.
We observed display bouts by walking between lek sites
and sampling any males that were displaying their erect
trains. For each bout, we recorded the time and the identity
of the male, as well as the following variables at 30-s
intervals: display behaviour with train erect (none, wing-
shake, train-rattle), any movement (walking forwards,
backwards, to the left or right, turning), whether there
were any females in sight and the location of any target
female to whom the male was clearly displaying. The
location of a target female was recorded as being in one of
the six 60° sectors around the male (Fig. 3a). At each 30-s
interval, we also measured the bearing (to the nearest 10°)
of the displaying m ale as the comp ass bearing (relative to
true north) of the axis through the male's body perpendic-
ular to the horizontal axis of the erect train (Fig. 3b). All
compass bearings taken in the field were corrected for
magnetic declination (National Geophysical Data Center
2008).
Behav Ecol Sociobiol
At each 30-s interval during a display bout, w e
determined the local sun azimuth using a solar angle
calculator that takes into account the date, time, latitude
and longitude (Gronbeck 2005). Using the sun azimuth, the
location of the target female and the bearing of the
displaying male (angle A in Fig. 3b), we then calculated
the foll owing angles of interest for further analysis: (1)
sunmale angle, as the clockwise angle between the sun's
azimuth and the bearing of the displaying male (angle B in
Fig. 3b) and (2) sunfemale angle, as the clockwise angle
between the sun's azimuth and the position of the female
relative to the male (angle C in Fig. 3b), using the median
angle for each of the six fema le position sectors (i.e. 300°,
0°, 60°, 120°, 180° or 240° for sectors 16, respectively, in
Fig. 3a).
In total, we co llected display data from 882 point
samples (at 30-s intervals) for 58 display bouts of 11
males. On average, we measured 16 point samples (range
366) per display bout and five display bouts (range 210)
per male. We analysed circular data according to Zar
(1999), where ā is the mean angle and VL (vector length) is
the length of the mean vector of a sample of angles. VL is a
measure of angular dispersion that ranges from 0 (highly
dispersed, adirectional sample) to 1 (highly directional such
that all measured angles are the same). For each of the
angles A, B and C in Fig. 3b, we calculated both a mean
angle and a vector length using the following procedures to
minimize pseudoreplication: first, we calculated ā and mean
VL for each bout using the procedure for first-order means
(Zar 1999, pp 599600). We then calculated ā and mean
VL for each individual male using a parametric second-
order analysis (Zar 1999). Finally, we performed a grand
mean analysis across males, using a further parametric
second-order analysis on the mean male values and testing
for directionality using the Hotelling procedure for second-
order samples (Zar 1999, pp 638639). This analysis tests
whether the distribution of angles in the second-order
sample differs significantly from uniform; if it does not
differ from a uniform distribution, then the 95% confidence
interval encompasses the circle and there is no mean angle,
ā. We also used the two-sample Hotelling test to compare
grand mean angles (Zar 1999, pp 641642).
Model presentation experiment
To control for the effects of female movement on male
orientation, we conducted experiments at LAA and BZ in
2008, present ing males wi th a taxidermically mounted
peahen in four different contexts, varying both the time of
day and the position of the model female. Trials were run in
the morning or the afternoon (AM or PM) with the model
female facing the male on either the EAST or WEST side of
his body and thus on the sunny or shaded side of his erect
train depending upon the time of day. Preliminary trials
indicated that males did not respond to the model if their
trains were not already erect. Thus, we selected males with
erect trains as they were encountered and randomly chose
the initial side (EAST or WEST) on which to place the
model. Subsequent trials for each male were run at different
timeside combinations, for a total of 33 trials with 17
different males (see ESM for details).
All model presentation trials were conducted with males
that were displaying their erect trains (but not wing-shaking
or train-rattling) with no live females in view. The model
female was placed about 2 m from the displaying male, and
we observed his response from 510 m to the north or
south. Trials were started when the male began to display in
a way that was clearly directed towards the model female
(usually <30 s after the model was set up). Male courtship
was considered to be directed towards the model when
males began to perform either the wing-shaking or train-
rattling display and moved towards the model. Each trial
was run for 5 min.
(a)
(b)
1
2
3
6
5
4
N
A
B
C
Fig. 3 a Diagram from above showing a displaying peacock with the
60° sectors used to identify the position of the female relative to the
male. b Angles of interest: A=male bearing, B=sunmale angle, C=
sunfemale angle
Behav Ecol Sociobiol
During each model presentation trial, we recorded data
at 30-s intervals as described above. Any trials where the
male did not respond to the model within 2 min by wing-
shaking or train-rattling were terminated and discarded.
Trials were also terminated prematurely if males attempted
to copulate with the model (n=8 trials), when male display
behaviour was no longer directed towards the model due to
the arrival of additional females (n=5 trials) or when males
lost interest in the model and stopped displaying or moved
away (n=5 trials). We have no reason to expect that the
male behaviour prior to the premature termination of a trial
was unusual in these cases, so we include all of these trials
in our analyses.
We analysed male responses during model presentation
trials in two ways. First, to quantify the type of display
(wing-shaking or train-rattling) initially performed in
response to the model, we used only the first point sample
from each trial. In all cases where the male displayed
continuously for the first 30 s of the trial, he performed
only one of these two display behaviours, so this first point
sample is a good measure of his initial, sustained response
to the model. To avoid pseudoreplication in this analysis,
we analys ed data only from the first experimental trial
performed with each individual male. Second, to examine
the overall directionality of the display response, we
calculated first-order mean angles for each trial and then
calculated a parametric second-order mean if more than one
trial type had been conducted with a given male in the same
time period (AM or PM) or for the same model placement
(EAST or WEST), and we used an addit ional parametric
second-order analysis to test for directionality across
individuals, as described above (Zar 1999).
Results
Peacock displays
Feral peacocks spend 1015% of their daytime time budget
displaying their erect trains during the breeding season
(Fig. 1; see also Walther 2003), and most of this activity
occurs during the morning and late afternoon (Petrie et al.
1991; Walther 2003; R. Dakin, personal observations).
When females are present, the wing-shaking display often
precedes the train-rattling display (Video 1 in the ESM),
and the train-rattling display always precedes copulation,
though the sequence of events during courtship can be
somewhat variable (Fig. 2; contra Petrie et al. 1992).
Although we rarely recorded complete display bouts,
this sampling method does not appear to have biassed our
results, since male behaviours (e.g. Fig. 2) and female
locations did not vary systematically during a display. For
example, for the longest recorded bout from each male
studied (n=11), the relation between bout length and the
proportion of point samples with females present was not
significant (Pearson correlation, r=0.27, p=0.42) nor was
the relation between bout length and the proportion of
samples where males were performing the wing-shaking
display (r=0.14, p=0.68). There was a significant positive
relation between bout length and the proportion of samples
during which males were performing the train-rattling
display (r=0.63, p=0.04), but this is not surprising given
that this display is relatively infrequently performed. There
was also no significant difference between the number of
point samples of each display type observed in the first or
second half of the observation period (paired t-tests: wing-
shaking, t=0.91, p=0.38; train-rattling, t=0.48, p=0.64, n
=
11). Finally, the relation between bout length and the vector
length for the mean male bearing was not significant (r=
0.17, p=0.62, n=11).
Female position during displays
When males performed the wing-shaking display, females
were generally standing behind them in sectors 46
(Fig. 4a; mean=83% of point samples per male, range=
53100%, n=11 mal es). This mean percentage is signifi-
cantly greater than 50% (one sample t-test, t=8.8, p<
0.0001, n=11 males). In fact, females were most often in
sectors 4 and 6 and rarely in sector 5 when they were
standing behind the male as he performed this wing-
shaking display. In contrast, males performed the train-
rattling display almost exclusiv ely when females were
standing directly in front (mean=98.6% of point samples
per male, range=90100%). Males often moved or turned
during the wing-shaking display when females were present
(mean=37% of point samples per male, range=086%), but
they generally did not move during the train-rattling display
(moving in mean=6% of point samples per male, range=0
30%). On average, males were significantly more likely to
move or turn during wing-shaking compared to train-rattling,
pooling across bouts for each male (Fig. 4b; paired t-test, t=
3.9, p=0.004, n=10 males).
Male orientation during displays
Although male displays were observed only on sunny days,
many of the male display courts were in full shade during
our observation periods. Despite this, there were no
significant differences between sun and shade in sunmale
angles (angle B in Fig. 3b) for either the wing-shaking
(two-sample Hotelling test , F=1.63, p=0.24, n=7 males in
sun, 8 males in shade) or train-rattling displays (F=0.76,
p=0.50, n=4, 7) nor for sunfemale angles (angle C in
Fig. 3b) in sun or shade for either the wing-shaking (F=
1.54, p=0.25, n=7, 8) or train-rattling displays (F=0.62,
Behav Ecol Sociobiol
p=0.56, n=4, 7). Thus, for these display situations, we
pooled data from displays in both sun and shade for
subsequent analyses.
When males had their train erect and females were not
present, males performed the wing-shaking display on
average 34% (range 0100%) of the time, pooling across
bouts for each male (n=10 males; one male was never
observed without a female present). When they were not
performing this display, they simply stood or walked about.
For males with their trains erect on sunlit courts when
females were absent, the grand mean sun male angle (angle
B) was significantly directional when males had their trains
erect (Fig. 5a; second-order Hotelling procedure, VL=0.46,
p=0.02, n=5) and the grand mean angle (ā=19.3°, 95%
CI=23435°) was not significantly different from (i.e.
males were facing generally towards the sun). In the
absence of females, the direc tion that males with their
trains erect faced on shaded courts was not significantly
directional (Fig. 5 b; ā =70.8°, VL=0.41, p=0.08, n=7).
Nonetheless, the difference between mean sunmale angles
in sun and shade was significant (F=8.19, p=0.01 , n=5, 7),
with males facing more directly towards the sun when they
displayed on sunlit courts.
When males had their trains erect and performed the
wing-shaking display while females were present, the grand
mean sunmale angle was not significantly directional
(Fig. 6a; VL=0.18, p=0.21, n=11 males), though the mean
sunmale angle (B) was fairly consistent for each male
(mean male VL=0.35±0.17 SD, 95% CI=0.240.47, n=
11), and seven of 11 males were significantly directional
(Fig. 6a). The grand mean sunfemale angle (C) was also
not significantly directional during the wing-shaking
display (Fig. 6c; VL=0.15, p=0.40, n=11), but mean
sunfemale angles were significantly directional for six of
a
b
Fig. 5 Sunmale angles when females were absent (n=10 males), for
displays on: a sunlit courts and b shaded courts. Grey vectors are the
means for each male, and the black vector is the grand mean across all
males. Mean vectors are drawn as solid lines when samples are
significantly non-random. The 95% confidence interval (shaded)is
shown for the grand mean. The outer circle has a radius of VL=1
wing-shaking train-rattling
0.0
0.1
0.2
0.3
0.4
0.5
0.6
mean proportion moving
123456
0.0
0.1
0.2
0.3
0.4
0.5
sector
mean proportion
front
back
Fig. 4 Tukey box plots showing a the proportion of point samples
where target females were positioned in each of the 60° sectors around
the male (see Fig. 3a) during wing-shaking displays and b the
proportion of point samples where males moved or turned during the
wing-shaking and train-rattling displays. Data were pooled over all
display bouts for each of 11 males, taking a mean for each male, so
that each box plot shows the distribution of the 11 male mean
proportions
Behav Ecol Sociobiol
the 11 males. It is noteworthy that females were on average
located on the shaded side of the male (i.e. away from the
sun) for all of these significant means (Fig. 6c).
In contrast, during the train-rattling display, the grand
mean sunmale angle (B) was highly directional (Fig. 6b,
VL=0.52, p=0.001, n=10 as one male was not observed
train-rattling). In this context, males faced generally
towards the sun, though the grand mean sunmale angle
(ā =43°) was significantly different from (95% CI=11
95°). The mean sunmale angle (B) during the train-rattling
display was also consistent within males (mean male VL=
0.67, 95% CI=0.510.83, n =10), with eig ht of ten
individual mean sunmale angles significant (Fig. 6b).
Results are nearly identical for the grand mean sunfemale
angle (C) in this context (Fig. 6d; VL=0.52, p=0.002, n=
10 males), with a grand mean angle of 44° (95% CI=13
93°), because females were almost always in sector 2
during this display. Thus, during the train-rattling display,
males were on average facing towards the sun at about 45°
to the right of the sun azimuth, and the female was almost
always stand ing directly in front of the male.
The two individuals who deviated most from this pattern
during train-rattling displays ha d the larges t sunmale
angles (ā =123° and 159°, VL=0.87 and 0.20, males A
and B, respectively, in Fig. 6 b). Both of these individuals
maintained display court s that were completely shaded
during our observations. Removing these two individuals
does not change the results for sunmale angle (VL=0.66,
p=0.0001, n=8); the grand mean sunmale a ngle (B)
without these two males shifts to 32°, but it is still
significantly different from (95% CI=6186°). Similarly,
the grand mean sunfemale angle (C) does not change
substantially when excluding these two males (VL=0.64, p=
0.0005, n=8, mean=33°, 95% CI=858°). Like the other
eight males, these two oriented their displays with the sun on
their left and the female directly in front.
Model presentation experiment
The type of display initially performed by a male after he
was presented with the female model (Table 1) did not
significantly depend upon either the time of day (AM vs.
A
B
A
B
ab
cd
Fig. 6 Sunmale (a, b) and
sunfemale (c, d) angles during
a, c wing-shaking (n= 11) and
b, d train-rattling (n=10)
displays. See Fig. 5 for
description of vectors
Behav Ecol Sociobiol
PM; Fisher exact test, p=0.34) or the location of the model
(EAST vs. WEST; p=0.34). Instead, the type of display
performed depended upon the position of the model relative
to the sun. Males were initially more likely to perform the
train-rattling display when the model was presented on the
sunny side of their erect trains (i.e. EAST in the AM and
WEST in the PM trials) and were significantly more likely
to perform the wing-shaking display when the model was
presented on their shaded side (Fisher exact test, p=0.03).
As when courting live females, males usually (10/12 trials)
positioned themselves with the model female behind their
erect train when they performed the wing-shaking display
and with the female directly in front for the train-rattling
display (all five trials where they performed this display).
The grand mean male compass bearing (angle A in Fig. 3b)
was not significantly directional when pooling EAST and
WEST trials but was significantly directional (or nearly so)
when pooling trials by time of day (Table 2). The grand mean
sunmale angle (B) tended to be significantly directional
regardless of the trial context and did not differ significantly
from (i.e. facing directly towards the sun; Table 2).
Comparisons of grand mean angles between different
trial types also indicate that the position of the sun, rather
than the model female, determined male display orientation.
Using data only from the first trial performed with each
individual (to avoid pseudoreplication), the grand mean
male compass bearing (A) was significantly different
between AM and PM trials (parametric two-sample
second-order test, F=11.9, p=0.0009, n=10, 7 males) but
not between EAST and WEST trials (F=0.5, p=0.64, n=
10, 7). There was no significant difference between grand
mean sunmale angles (A) when comparing either AM and
PM (F=0.5, p=0.61, n=10, 7) or EAST and WEST trials
(F=0.4, p=0.66, n=10, 7).
Discussion
Our observational and experimental results demonstrate that
the direction that peacocks face during their pre-copulatory
courtship display is influenced by the position of the sun.
The train-rattling display was significantly directional, with
males oriented at about 45° to the right of the sun azimuth,
on av erage, and with the target female almost always
positioned directly in front of the male's erect train (Fig. 6b,
d). Moreover, these angles were the same whether or not
the male displayed in sun or shade. This finding is
remarkable for three reasons. First, it strongly suggests that
the males' iridescent plumage colours are an important
component of courtship signalling and female choice (see
also Loyau et al. 2007a). Thus, although the number of
eyespots on the male's train may not influence female
choice in some populations (Dakin and Montgomerie
unpublished data; Takahashi et al. 2008), the colour of
those eyespots or other male colours appear to be important
Table 1 Initial display res ponses of males to a model female
presented in different experimental contexts: morning or afternoon
and on the east or west side of the male. For AM-EAST and PM-
WEST trials, the model was on the sunlit side of the male's erect train;
for AM-WEST and PM-EAST trials, she was on the shaded side
Male display
Experimental context (n) Wing-shaking Train-rattling
Time of day
AM (10) 6 4
PM (7) 6 1
Model location (compass)
EAST (10) 6 4
WEST (7) 6 1
Model location (sun)
Sunlit side (9) 4 5
Shaded side (8) 8 0
Mean angle
Experimental context (n)VL Fp ā 95% CI
Male bearing
AM (12) 0.33 3.0 0.10 99.7°
PM (9) 0.61 26.8 0.0005 277.2° 236321°
EAST (14) 0.19 0.9 0.44
WEST (13) 0.08 0.1 0.91
Sunmale angle
AM (12) 0.34 3.1 0.09 357.4°
PM (9) 0.59 20.7 0.001 5.8° 32154°
EAST (14) 0.36 4.4 0.04 16.1° 318101°
WEST (13) 0.53 12.6 0.001 358.6° 32442°
Table 2 Directionality of male
display responses to a model
female by experimental context.
For male bearing, refers to
true north; whereas for sun
male angle (B in Fig. 3b),
refers to the sun azimuth.
(Statistics are for parametric
second-order tests of
directionality for circular data;
samples that are significantly
directional are in italics)
Behav Ecol Sociobiol
sexual signals. Second, our results suggest that males either
use the plane of polarization or their previous experience to
locate the position of the sun as it changes through the day.
There is some evidence that birds can detect the e-vector of
polarized light (Able 1982), and this would be visible as
long as the birds could see open sky. Males clearly knew
where the sun was, and they attempted either to move
themselves or to manipulate the target females (live and
experimental) so that the target female was on the sunny
side of their erect train, whether or not they displayed in the
full sun. Finally, we found that the males consistently
oriented their erect trains in such a way that the sun was
always on the male's left side. The reasons for the
consistency of this sunmal e angle are unknown and will
require further study, but the lateralization of courtship
behaviour may also be important in maximizing signal
efficacy.
Males usually performed the wing-shaking display while
facing away from females (Fig. 4a) and, as a result, their
conspicuously moving, orange-coloured wings could serve
to attract female attention. Males may use the wing-shaking
display to corral target females into a position on the sunny
side of their erect train for subsequent train-rattling dis-
plays. This hypothesis is strongly supported by our model
presentation trialsby controlling female movement, this
experiment demonstrates that males will generally perform
the wing-shaking display when the female is positioned on
the shaded side of their erect train, versus always train-
rattling when the female is positioned on the sunny side
(Table 1). Thus, the directionality of the train-rattling
display that we observed under natural conditions is clearly
due to male behaviour and not simply to peahens attempt-
ing to view the males' trains from the sunny side, although
it is possible that females also prefer to do this.
While there was no overall consistency across males in
the orientation of their wing-shaking displays, the majority
of individual males did show significant directionality
during this display (Fig. 6a). Male display courts varied in
the size and location of sheltering features and in their
location relative to preferred female foraging and resting
sites and thus high female traffic (unpublished data). As a
consequence, the most common direction of approach for
females, and thus the direc tion males faced when attempt-
ing to attract new visitors, varied among males.
While we have focused this study on the analysis of
peacock displays on sunny days, peacocks will certainly
display on overcast days (unpublished data). Hamilton
(1965) reported that, on cloudy days, the directionality
normally seen in Anna's hummingbird dives was no longer
apparent, and this might be expected in peacocks. It would
be an interesting natural experiment to compare the patterns
of male display behaviour and directionality on clear days
with those of overcast days when light is diffuse. It would
also be interesting to compare male display behaviour in
different peafowl populations worldwide, since birds in
North Ameri can populations experience different light
environments and lek in different habitats than those in
India and Southeast Asia. Nonetheless, our comparison of
sunlit and shaded courts suggests that males know the
position of the sun at different times of day and orient their
displays accordingly, and they should be able to do this
anywhere in the world.
If orientation towards the sun is important for male
signal efficacy, why do some peacocks choose shaded
display courts? Display court selection most likely involves
a number of factors, including proximity to food sources
where females congreg ate (Loyau et al. 2007b), proxi mity
to closely related males (Petrie et al. 1999), distance from
agonistic males and predators, and shelter from the wind.
For example, one male in this study maintained a display
court directly to the west of a tall building and thus his
court was completely shaded th roughout the morning.
Nevertheless, he received a high rate of female visitation
apparently because his territory was adjacent to a popular
dust-bathing site that attracted many females, consistent
with the hot-spot theory of lek formation (Bradbury and
Gibson 1983). Display court selection is no doubt complex,
and presumably it would not be advantageous for males to
choose a well-lit territory in an area that would receive no
visitors or for males to forego display d uring periods of
shade or cloud.
Of the train-rattling display, Darwin (1871) said that
peacocks and birds of paradise rattle their quills together,
and the vibratory movement apparently serves merely to
make a noise, for it can hardly add to the beauty of their
plumage. However, we believe these rapid feather move-
ments might help to display the feathers' iridescence.
Preliminary evidence suggests that the iridescent eyespot
coloration of the peacock's train is important for mate
choice (Loyau et al. 2007a; Dakin and Montgomerie,
unpublished data) and may be an honest signal of male
quality.
The benefit to males of orienting at such a consistent
angle relative to the sun is not yet clear. One possibility is
that it improves the efficacy of the colour signal from their
train, allowing females to discriminate more easily among
individual m ales and to more accurately assess male
quality. Perhaps a 45° sunmale angle minimizes specular
reflectance from the eyespots or produces a particular
iridescent effect or hue that females prefer. None of these
explanations, however, help us to understand why males
were usually oriented to the right of the sun during train-
rattling displays (Fig. 6b). Laterality in courtship displays
(Snow 1961; Workman and Andrew 1986) and copulation
behaviour (Ventolini et al. 2005) has been documented in
several other bird species, and in bird song is thought to be
Behav Ecol Sociobiol
due to the laterality of avian brain function (Nottebohm
1971). Interestingly, all of the phylogenetically closest
relatives of peafowl (genus Polyplectron and the argus
pheasants Argusianus argus and Rheinartia ocella ta)
display their fan-like ornamental tail plumage in a lateral
posture, where males present only one side of their body to
visiting females (Kimball et al. 2001). Although peafowl do
not use this side-on posture, there may be strong laterali-
zation for courtship function throughout the clade.
While there is still much to be learned about the complex
displays and ornaments of peacocks, our study strongly,
albeit circumstantially, argues against the notion that the
male train is not an important signal to females, as
Takahashi et al. (2008) contend. It seems to us unlikely
that the complex male displays that we describe here would
be maintained with such precision if they did not influence
female choice. That the males appear to be orienting their
trains to influence the efficacy of their colour signals further
reinforces the evidence that the train ornament and the
iridescent colours of the eyespots (e.g., Loyau et al. 2007a)
are products of sexual selection that females attend to when
choosing a mate.
Acknowledgement We thank the Assini boine Park Zoo , Los
Angeles Arboretum and Bronx Zoo for logistic support and Robert
Ewart, Jason Clarke and Lori Parker for assistance in the field. Vanya
Rohwer expertly prepared the model peahen, and Nick Roberts helped
us understand the nature of polarized light cues. We thank Barrie Frost
for his helpful suggestions. Funding was provided by a Natural
Sciences and Engineering Research Council of Canada (NSERC)
scholarship and the Society for Canadian Ornithologists' Fred Cooke
Award to RD and by NSERC Discovery and equipment grants to RM.
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Feathers act as vibrotactile sensors that can detect mechanical stimuli during avian flight and tactile navigation, suggesting that they may also detect stimuli during social displays. In this study, we present the first measurements of the biomechanical properties of the feather crests found on the heads of birds, with an emphasis on those from the Indian peafowl ( Pavo cristatus ). We show that in peafowl these crest feathers are coupled to filoplumes, small feathers known to function as mechanosensors. We also determined that airborne stimuli with the frequencies used during peafowl courtship and social displays couple efficiently via resonance to the vibrational response of their feather crests. Specifically, vibrational measurements showed that although different types of feathers have a wide range of fundamental resonant frequencies, peafowl crests are driven near-optimally by the shaking frequencies used by peacocks performing train-rattling displays. Peafowl crests were also driven to vibrate near resonance in a playback experiment that mimicked the effect of these mechanical sounds in the acoustic very near-field, reproducing the way peafowl displays are experienced at distances ≤ 1.5m in vivo . When peacock wing-shaking courtship behaviour was simulated in the laboratory, the resulting airflow excited measurable vibrations of crest feathers. These results demonstrate that peafowl crests have mechanical properties that allow them to respond to airborne stimuli at the frequencies typical of this species’ social displays. This suggests a new hypothesis that mechanosensory stimuli could complement acoustic and visual perception and/or proprioception of social displays in peafowl and other bird species. We suggest behavioral studies to explore these ideas and their functional implications.
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The South-east Asian pheasant genus Polyplectron is comprised of six or seven species which are characterized by ocelli (ornamental eye-spots) in all but one species, though the sizes and distribution of ocelli vary among species. All Polyplectron species have lateral displays, but species with ocelli also display frontally to females, with feathers held erect and spread to clearly display the ocelli. The two least ornamented Polyplectron species, one of which completely lacks ocelli, have been considered the primitive members of the genus, implying that ocelli are derived. We examined this hypothesis phylogenetically using complete mitochondrial cytochrome b and control region sequences, as well as sequences from intron G in the nuclear ovomucoid gene, and found that the two least ornamented species are in fact the most recently evolved. Thus, the absence and reduction of ocelli and other ornamental traits in Polyplectronare recent losses. The only variable that may correlate with the reduction in ornamentation is habitat, as the two less-ornamented species inhabit montane regions, while the ornamented species inhabit lowland regions. The implications of these findings are discussed in light of models of sexual selection. The phylogeny is not congruent with current geographical distributions, and there is little evidence that Pleistocene sea level changes promoted speciation in this genus. Maximum likelihood and maximum parsimony analyses of cytochrome b sequences suggest that the closest relatives of Polyplectron are probably the peafowl and the argus pheasants.