Yodels - Youngstown State University

Structural and Contextual Characteristics
of Territorial “Yodels” Given by
Male Common Loons (Gavia immer)
in Northern Wisconsin
John N. Mager, III
Department of Biological and Allied Health Sciences
Ohio Northern University
Ada, Ohio 45810
419. 772. 2333
[email protected]
Charles Walcott
Department of Neurobiology and Behavior
Cornell University
Ithaca, New York 14853
ABSTRACT
Although Common Loons (Gavia
immer) are recognized for their dynamic
vocal repertoire, we still know very little
about the information that is communicated by these signals. Male loons give a
vocalization called the yodel. We assessed
the acoustic structural characteristics of the
yodel and the ecological context in which
males within a population of individuallybanded loons in northcentral Wisconsin
yodeled. From behavioral observations during the course of the 2002 breeding season,
we found that males yodeled mostly in response to other loons that had either flown
over or landed upon their territories. Males
also yodeled more frequently early in the
breeding season when territories are being
reestablished, and at the time when the
chicks are hatching—a critical period with
respect to annual reproductive success.
These results confirm previous hypotheses
that the yodel functions as a territorial
threat signal.
INTRODUCTION
Common Loons (Gavia immer) are
long-lived, seasonally-monogamous,
migratory waterbirds that defend allpurpose breeding territories from
both conspecific (Rummel and Goetzinger 1975, 1978, McIntyre 1988)
and interspecific (Kennedy 1981,
Sperrey 1987, Kirkham and Johnson
1988) intruders. One of the most
charismatic features of this species is
its dynamic vocal repertoire that consists of three long-range vocalizations:
327
328
Structural and Contextual Characteristics of Territorial “Yodels”
Figure 1. Sound spectrogram (above) showing the change in frequency (in kilohertz), and
waveform (below) showing the change in energy (in micropascals) of a typical yodel over time (in
seconds). Structurally, the yodel consists of two features: an introductory phrase of 3-4 notes that
rise in frequency, and a motif of 2-syllable repeat phrases that follows the introductory phrase.
the wail, the tremolo, and the yodel
(see Barklow 1979, McIntyre 1988,
Vogel 1995, and Lindsay 2002). Of
these three, the yodel can be considered the “song” of the Common Loon
in that it is (following Catchpole and
Slater 1995) a long, complex vocalization given only by males during the
breeding season primarily in response
to conspecific intrusions.
Structurally, the yodel is composed
of two distinguishing features: an introductory phrase of 3–4 notes that
rise in frequency, and a series of 2-syllable repeat phrases that follows the
introductory phrase (Fig. 1). Hypotheses of the function of the yodel
have ranged from those associated
with mate attraction (Sim 1923, Sjølander and Årgen 1972) to those that
currently consider it a territorial
threat signal (Munro 1945, Rummel
and Goetzinger 1975, 1978, Barklow
1979, Young 1983, McIntyre 1988,
Wentz 1990, Vogel 1995, Lindsay
2002). Hypotheses regarding the information communicated by the
yodel include individual or class
(e.g., neighbor/non-neighbor) identity (Barklow 1979, 1979b, Miller
1988, Vogel 1995, Walcott et al. 1999,
Walcott and Evers 2000, Lindsay
2002), internal “motivation” or willingness to escalate an aggressive interaction (Barklow 1979), and/or the
physical condition (Lindsay 2002) of
an individual. Although all of these
hypotheses regarding the function of
the yodel seem reasonable, they have
yet to be tested with much rigor in
the field. In the present study, we
begin an investigation of these hypotheses by assessing the characteristics of yodels as well as the behavioral
context in which males within a population of individually-banded loons
in northern Wisconsin yodeled during the breeding season.
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The Passenger Pigeon, Vol. 69, No. 3, 2007
METHODS
Study Area
We conducted this study during
the 2002 breeding season within a
group of roughly 200 lakes located
within Oneida County, Wisconsin,
northwest of the city of Rhinelander
(latitude N 45° 42′, longitude W 89°
37′; see Meyer et al. (1998) for ecological characteristics). Since 1991,
biologists have individually-banded,
and have monitored the productivity,
behavior, and environmental threats
to this population (see Piper et al.
1997a, 1997b; 2000; 2002; Meyer et
al. 1995; 1998), making it one of the
longest continuously studied populations of banded loons in the country
(Evers et al. 2000).
Common Loons within this population are seasonally monogamous
(Piper et al. 1997a), exhibit high territory and mate fidelity (Piper et al.
2000), and aggressively defend all-purpose breeding territories from conspecifics. Soon after the winter ice has
melted, males return to the area and
establish territories and form pair
bonds with returning females. Breeding pairs begin nesting usually within
a month after returning to their territories. Females lay 1–2 eggs per nesting attempt, and both parents share in
incubating duties for 25–28 d (Strong
and Hunsicker 1987; McIntyre 1988;
Evers 1994; Mager 1995; Paruk 2000).
Subprecocial chicks hatch asynchronously within a 24-h period, establish
dominance, and are fed and protected from threats (including conspecifics) by both parents until they
fledge 8–10 weeks after hatching
(McIntyre 1988; McIntyre and Barr
1997; Mager 2000). Both male and fe-
male loons frequently intrude on the
territories of other loons during the
breeding season. Such intrusions
probably function as a way for intruders to assess the quality of a breeding
territory (Piper et al. 2000). At times,
intrusions escalate into dangerously
aggressive interactions between individuals, and can lead to displacement
or even death of individuals (Paruk
1999; Piper et al. 2000).
Protocol for eliciting, recording,
and measuring yodels.
To acquire an adequate sample of
yodels from each individual while
minimizing disturbance, we gathered
at least ten yodels from each male
within the population each year. We
obtained yodels from individuals by:
(1) recording them in situ during 1-h
time-activity budget behavioral samples in the field, and/or (2) by recording them as males responded to a
series of broadcasted recordings of
loon vocalizations (wails, tremolos,
flight tremolos, and yodels) over no
more than four 20-min sampling periods. To elicit yodels, we broadcast
compact disk recordings of loon vocalizations through a RadioShack PowerHorn megaphone at ~70–80 dB from
a distance of ~100 m from the focal
subject, but adjusted the intensity of
recordings as loons approached or
retreated from the speaker. We
recorded yodels onto digital audio
tapes (DAT) using a Sennheiser MKH70 shotgun microphone connected to
HHB PortaDAT recorder at a sampling rate of 44.1 kHz, and then
downloaded and converted these
recordings into digital audio (AIFF)
files using the Canary sound analysis
software package (v. 1.5, Cornell Uni-
Structural and Contextual Characteristics of Territorial “Yodels”
330
Table 1. Measured and calculated parameters of yodels analyzed.
Parameter
Definition
Frequency Parameters
FINTRO1Uw
Frequency (in kHz) with highest intensity at end of second harmonic of first note
of introductory phrase (from Walcott, et al. 1999)
FINTRO3w
Frequency (in kHz) with highest intensity at end of third note of introductory
phrase (from Walcott, et al. 1999)
PFINTRO3
Peak frequency (in kHz) of entire third note of introductory phrase
PFALLRPT
Peak frequency (in kHz) of entire motif of repeat phrases
PFRPTx
Peak frequency (in kHz) of repeat phrase x
PFS1RPTx
Peak frequency (in kHz) of first syllable of repeat phrase x
PFS2RPTx
Peak frequency (in kHz) of second syllable of repeat phrase x
Duration/Latency Parameters
#R
Number of repeat phrases in entire yodel
DENT
Duration (in seconds) of entire yodel
DINTRO
Duration (in seconds) of introductory phrase
DINTROw
Duration (in seconds) of second and third notes of introductory phrase (from Walcott, et al. 1999)
DGAPx
Latency (in seconds) of time before repeat phrase x
DRPTx
Duration (in seconds) of entire repeat phrase x
versity Bioacoustics Research program). With this program, we used a
fast Fourier transformation (using a
349.7 Hz bandwidth, 4096 points per
frame, 50% overlap of frames in successive transforms, and a Hamming
sampling window) to generate sound
spectrograms from which we measured a number of frequency, latency,
and duration parameters of each
yodel (Table 1). Following previous
work by Barklow (1979) and Vogel
(1995), we also calculated a “ratio of
coefficient of variation” (CV, or the
standard deviation expressed as a percentage of the mean, calculated as
(s × 100)/ Y, where s is the standard
deviation and Y is the arithmetic mean
of the data set—see Sokal and Rohlf
1997) between individuals (CVb)/
average CV within individuals (CVi) to
determine those acoustic parameters
that exhibit a low within-individual
variability yet high between-individual
variability. These, in turn, could help
determine which parameters could be
used by loons to discriminate individuals.
Behavioral Observations
We conducted behavioral observations of territorial pairs of loons during the entire 2002 breeding season
(between 15 April, when winter ice
melted, and 12 October, when all
males had left their breeding territories and which was roughly 3 weeks before winter ice returned). Behavioral
observations consisted of 1-hour continuous samples of focal pairs roughly
3-4 times each week and between 0430
and 1400h each day, where we
recorded information regarding the
type of yodel (crouch- or vultureposture, see McIntyre, 1988 for description), the intended recipient of
the signal, and the number of repeat
phrases given per yodel. We assessed
weekly changes in yodeling rate (# yodels/hour of observation) both with
Julian calendar date as well as the
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The Passenger Pigeon, Vol. 69, No. 3, 2007
Table 2. Means and ranges of yodel frequency, duration, and latency measurements recorded from
individual male Common Loons caught in Oneida County, Wisconsin, in 2002.
Measurementa
Mean ± 1 S.E.
Frequency Parameter
FINTRO1Uw
FINTRO3w
PFINTRO3
PFALLRPT
PFRPT1
PFS1RPT1
PFS2RPT1
Range
CVi
CVb
CVb
CVi
1.480
1.803
1.787
1.737
1.741
1.795
1.705
± 0.007 kHz
± 0.056 kHz
± 0.013 kHz
± 0.028 kHz
± 0.031 kHz
± 0.019 kHz
± 0.031 kHz
1.277–1.602 kHz
1.508–2.242 kHz
1.300–2.138 kHz
1.045–2.127 kHz
1.045–2.245 kHz
1.079–2.245 kHz
1.045–2.214 kHz
0.019
0.017
0.041
0.049
0.054
0.045
0.065
0.028
0.172
0.041
0.090
0.099
0.060
0.101
1.474
10.118
1.000
1.837
1.833
1.333
1.554
Duration/Latency Parameter
#R
3.342
DENTYODEL
6.477
DENTINTRO
1.741
DINTROw
0.954
DGAP
0.305
DRPT1
1.131
± 0.216 kHz
± 0.291 kHz
± 0.031 kHz
± 0.032 kHz
± 0.015 kHz
± 0.025 kHz
0–15 repeat phrases
1.672–17.083 sec
0.370–2.645 sec
0.213–1.936 sec
0.147–1.888 sec
0.270–1.832 sec
0.372
0.277
0.095
0.104
0.156
0.044
0.494
0.250
0.118
0.184
0.269
0.125
1.328
0.903
1.242
1.769
1.724
2.841
aRefer
to Table 1 for definitions of yodel parameters.
period within the breeding season relative to the hatching date. We assessed
not only changes in seasonal rates of
yodeling, but also whether these rates
corresponded with conspecific intrusion by looking at the number of flyovers and intrusions upon the
breeding territories.
RESULTS
Structural Characteristics of
Yodels of Oneida County Males
There was considerable variability
in the frequency and timing characteristics of their yodels (Table 2).
Some frequency parameters, such as
FINTRO1Uw and FINTRO3w, showed
very little within-individual variability
(CVi, Table 2). Other parameters,
such as the latency parameter DGAP,
exhibited high between-individual
variation (CVb, Table 2). Only one parameter, FINTRO3w, exhibited a
CVb/CVi score significantly larger
than the other parameters suggesting
it might be used by loons for individual recognition. From a qualitative examination of spectrograms generated
from recording the same yodel at various distances, those features of the
sound which best resist attenuation
with distance (i.e., 300–400 m) were
the peak frequency and duration of
the yodel that includes the third note
of the introductory phrase and the
motif of repeat phrases (Fig. 2).
Behavioral Context in which Yodels
Are Given
Seasonally, males yodeled mainly
between May and July, and rarely yodeled after their chicks were roughly
nine weeks old, when presumably
chicks are fledging from parental care
(Fig. 3). The rate at which males yodeled peaked twice during 2002: (1)
right after winter ice had melted from
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Structural and Contextual Characteristics of Territorial “Yodels”
Figure 2. Acoustic spectrograms (plotting changes in frequency [in Kilohertz] over time [in
seconds]) of a yodel recorded at various distances (from top to bottom, 50, 100, 200, 300, and 400
m.) over an open lake. Qualitatively, individual timing and latency elements are lost with the
distance while dominant frequencies (those of the final note of the introduction and of the repeat
phrases) and the entire duration of these frequencies are maintained.
The Passenger Pigeon, Vol. 69, No. 3, 2007
lakes, and (2) at the time of year
chicks were hatching (ANOVA F1,521 =
16.061, P < 0.0001, N = 24 males, Fig.
3). Most of the yodels given were in response to conspecifics (Fig. 4), and
corresponded with times when conspecifics either flew over or intruded
upon the resident male’s territory (coefficient of correlation, r = 0.183,
F1,429 = 14.905, P < 0.0001, N = 24
males).
DISCUSSION
Empirical evidence from this study
supports the notion that the yodel is a
territorial signal that is given in response to territorial intrusions primarily by conspecifics. Seasonally, yodels
were given most frequently when males
returned to their breeding territories
just after winter ice had melted. This is
believed to be a period when males are
not only establishing/reestablishing
territories, but also establishing/
reestablishing pair bonds with mates.
As such, in addition to a signal that declares ownership, there is the possibility that the signal also functions to
reestablish pair bonds between males
and females. This, in turn, would require a need for acoustic parameters
within the territorial signal that would
facilitate individual recognition. Like
the studies by Barklow (1979) and
Vogel (1995), analysis of individual frequency, duration, and latency elements
of the yodels recorded in 2002 reflects
frequency features of the yodel (particularly FINTRO3w, see Table 2) that exhibit low intra-individual variation and
high inter-individual variation. As such,
these features may be ideal candidates
for communicating individual identity.
However, other studies have shown
333
that there are individually-distinguishing suites, rather than individual
acoustic features of the yodel, that
might facilitate individual recognition
(Walcott et al. 1999, Lindsay 2002,
Mager 2005).
Although the ability to distinguish
individuals using these mathematical
tools to analyze their yodels may lead
to potential features of the yodel that
might permit individual recognition
among loons, it does not necessarily
mean that the loons actually use these
characteristics to recognize individuals.
One way to determine if loons pay attention to these parameters is to use an
acoustic playback study that compares
the responses of individuals to yodels
that vary in these potential characteristics. Data from two preliminary studies
indicate that loons are able to discriminate between the yodels from territorial neighbors and non-neighbors
(Lindsay 2002, Mager 2005) as well as
the possibility that females are able to
distinguish between the yodels of their
mates and the yodels of non-mates
(Vogel 1995). However, because no
study has manipulated specifically the
individual, or suite of potential
acoustic individually-distinguishing features of the signal that have been identified in previous studies, it still is
uncertain as to what feature loons are
paying attention in order to discriminate between individual males.
In addition to a peak in yodeling
rate with the return and reestablishment of territories/mates, we detected a peak in the rate at which
males yodeled during the breeding
season at a point when chicks were
about to hatch. This should not be
surprising, as this period is one of the
most critical of the breeding season to
a breeding pair in terms of the risk of
334
Structural and Contextual Characteristics of Territorial “Yodels”
Figure 3. Bar graphs representing mean weekly yodeling rates of 24 male loons that fledged chicks
during the 2002 breeding season. The top figure represents the weekly change in yodeling rate
during the Julian calendar year beginning at the point of ice-out and ending 2-3 weeks prior to iceon, when a majority of males had already left for the winter. The bottom figure represents the
mean weekly yodeling rates of the same individuals during the breeding season relative to the
hatching date, with negative values on the x-axis representing the weeks prior to the day of
hatching and positive values representing weeks after the day of hatching. Rates were determined
from 580 1-hour behavioral sampling periods.
reproductive failure, and might necessitate a period of greater awareness of
potential intruders and vigilance in
their removal. The nesting period is
the most critical period of the breed-
ing season, as the failure to successfully hatch eggs (not the failure of
parents to nest, nor the failure of parents to successfully fledge hatched
chicks) is the biggest reason why resi-
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The Passenger Pigeon, Vol. 69, No. 3, 2007
Figure 4. Pie-chart of the perceived targets of loon yodels. Males yodeled primarily at other
Common Loons, but also in response to human intrusions/disturbances.
dent pairs experience reproductive
failure during the breeding season
(Mager 2005). As such, in terms of reproductive fitness, it is the period
when loons have the most to lose.
Therefore, loons should be the most
attentive to territorial intrusions and
protective of their nests/offspring
during this period of the breeding
season. This, in turn, can explain the
peak in the number of yodels given by
males during this period.
The two acoustic parameters transmitted over the greatest distances
were: (1) the peak frequency and duration of the yodel that includes the
third note of the introductory phrase
and (2) the number of repeat phrases.
Acoustically, because the frequencies
that are incorporated in these notes
characteristically exhibit minimal attenuation (McIntyre 1994), it is not
surprising that these parameters hold
up better than others over a substantial distance. However, it makes one
wonder if these two parameters of the
yodel are important to long-distance
territorial communication; and if so, it
begs the question as to what information is communicated by the frequency and duration of this aspect of
the yodel. In preliminary work, we
have found that the pitch of the third
note and the number of repeat syllables may communicate information
regarding the relative fighting ability
and aggressive “motivation” of each
male, respectively. The peak frequency of this part of the yodel is correlated strongly with loon body weight
and condition—larger males tend to
produce lower-frequency yodels and
loons appear to respond with more
alarm to lower-frequency yodels
(Mager et al. 2007). Since weight and
condition are related to the ability of a
male to acquire and hold onto a territory (Evers 2001), this frequency parameter may indeed communicate
something about male fighting ability
and/or condition. Additionally, each
loon can increase the number of repeat syllables and thus vary the duration of the yodel. Loons produce
336
Structural and Contextual Characteristics of Territorial “Yodels”
longer yodels when the value of a resource is enhanced or when the risk of
retaliation increases (see Mager
2005). This finding supports Barklow’s hypothesis (1979) that yodel duration communicates information
regarding the “motivation” or willingness to escalate a contest. Therefore,
we believe that, with this part of the
yodel, loons may be communicate
both how strong a competitor they are
and how “motivated” or willing they
are to escalate a contest.
In conclusion, it appears that the
yodel is a territorial threat signal that
is given both when males are reestablishing territories and pair bonds as
well as during the most critical period
of the breeding season in terms of reproductive fitness. An analysis of the
variability in acoustic features of the
yodel, as well as an analysis as to how
the yodel attenuates over distances,
suggests there are many characteristics of the yodel that would facilitate
long-distance communication of identity, as well as the communication of
individual fighting ability and motivation. Only with further analyses and
playback studies can we elucidate the
importance of these features in the
signaling strategies of male loons.
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Jay Mager teaches ecology and ornithology
as an assistant professor of Biological &
Allied Health Sciences at Ohio Northern
University. He was formerly in the Department of Neurobiology and Behavior at Cornell University and has spent the past 16
years researching the life history and behavioral ecology of common loons, focusing
on parental care strategies as well as the
role acoustic communication plays when
loons select breeding territories.
Charlie Walcott is a professor of Neurobiology and Behavior at Cornell University
and former director of the Cornell Laboratory of Ornithology. When not studying the
ecology and acoustic behavior of loons, he
serves at the Dean of the University Faculty
at Cornell.
Red-bellied Woodpecker at the suet was caught by John Krerowicz.
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