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Song Sparrow (Melospiza melodia) song varies with urban noise



Dans les environnements urbains, les bruits d'origine anthropique pourraient masquer les chants d'oiseaux, particulièrement les notes émises à basses fréquences (1–2 kHz). Les oiseaux qui vivent en milieux urbains pourraient modifier leur chants, particulièrement les portions à basse fréquence, pour minimiser le masquage par les bruits d'origine anthropique. De telles modifications ont été observées chez Parus major aux Pays-Bas, ainsi que chez certains mammifères. Nous avons étudié Melospiza melodia, qui est une espèce commune dans les environnements urbains et ruraux, un peu partout en Amérique du Nord. Nous avons enregistré les chants de 28 mâles en liberté à Portland, en Orégon. Nous avons également mesuré l'amplitude et le spectre des bruits ambiants sur des lieux de chants. Les Melospiza melodia qui chantaient aux sites les plus bruyants montraient des notes basses de plus haute fréquence et avaient relativement moins d'énergie (amplitude) dans la gamme des basses fréquences de leurs chants (1–4 kHz), où la plupart des bruits d'origine anthropique ont lieu. Bien que le (ou les) mécanisme(s) qui est (sont) à l'origine de cette corrélation est (sont) encore indéterminé(s), la correspondance observée entre les chants et les bruits pourrait résulter d'une plasticité comportementale. Nous discutons dans l'article des explications qui concernent ces patrons et de la façon de les tester.
W E. W  S M. Y
Biology Department, Reed College, 3203 SE Woodstock Boulevard, Portland, Oregon 97202, USA
A.—In urban environments, anthropogenic noise may mask bird song,
especially the notes occurring at lower frequencies (1–2 kHz). Birds living in urban
environments may modify their songs, particularly the low-frequency portions, to
minimize masking by anthropogenic noise. Such modifi cations have been observed
in Great Tits (Parus major) in The Netherlands, as well as in some mammals. We
studied Song Sparrows (Melospiza melodia), which are common in both urban and
rural environments in much of North America, and recorded the songs of 28 free-
living males in Portland, Oregon. We also measured the amplitude and spectrum of
ambient noise at singing locations. Song Sparrows singing at noisier locations exhib-
ited higher-frequency low notes and had relatively less energy (amplitude) in the
low-frequency range of their songs (1–4 kHz), where most anthropogenic noise also
occurred. Although the mechanism(s) producing the correlation are as yet unde-
termined, the observed match between song and noise may result from behavioral
plasticity. We discuss explanations for these pa erns and how to test them. Received
4 April 2005, accepted 10 October 2005.
Key words: anthropogenic, Melospiza melodia, ontogeny, song, Song Sparrow,
urban noise.
Le Chant de Melospiza melodia Varie avec le Bruit Urbain
R.—Dans les environnements urbains, les bruits d’origine anthropique
pourraient masquer les chants d’oiseaux, particulièrement les notes émises à basses
fréquences (1–2 kHz). Les oiseaux qui vivent en milieux urbains pourraient modifi er
leur chants, particulièrement les portions à basse fréquence, pour minimiser le
masquage par les bruits d’origine anthropique. De telles modifi cations ont été
observées chez Parus major aux Pays-Bas, ainsi que chez certains mammifères. Nous
avons étudié Melospiza melodia, qui est une espèce commune dans les environnements
urbains et ruraux, un peu partout en Amérique du Nord. Nous avons enregistré les
chants de 28 mâles en liberté à Portland, en Orégon. Nous avons également mesuré
l’amplitude et le spectre des bruits ambiants sur des lieux de chants. Les Melospiza
melodia qui chantaient aux sites les plus bruyants montraient des notes basses de plus
haute fréquence et avaient relativement moins d’énergie (amplitude) dans la gamme
des basses fréquences de leurs chants (1–4 kHz), où la plupart des bruits d’origine
anthropique ont lieu. Bien que le (ou les) mécanisme(s) qui est (sont) à l’origine de
ce e corrélation est (sont) encore indéterminé(s), la correspondance observée entre
les chants et les bruits pourrait résulter d’une plasticité comportementale. Nous
discutons dans l’article des explications qui concernent ces patrons et de la façon de
les tester.
Address correspondence to this author. Present address: Biology Department, Bishop’s University,
Lennoxville, Quebec J1M 2A7, Canada. E-mail:
The Auk 123(3):650–659, 2006
© The American Ornithologists’ Union, 2006.
Printed in USA.
Song and NoiseJuly 2006]
T   birds are remarkably variable,
and studies have o en found that even slightly
dissimilar songs diff er in communicative function
and effi cacy (Catchpole and Slater 1995, Marler
and Slabbekoorn 2004). Therefore, understand-
ing the precise ways in which acoustic signals
vary, how this variation arises, and the ecological
and evolutionary consequences of song variation
are central questions in animal communica-
tion today (Bradbury and Vehrencamp 1998,
Slabbekoorn and Smith 2002a).
The environment in which acoustic signals
are emi ed and transmi ed has strong eff ects
on vocal signals. The physical structure of the
habitat infl uences degradation of sounds, which
can aff ect the evolution of signal structure and
signal delivery behaviors to increase transmis-
sion (Hunter and Krebs 1979, Pa en et al. 2004).
Similarly, presence of acoustically overlapping
signalers or noise from wind or water may
favor changes in the time and place of signaling
(Wiley and Richards 1982, Lengagne and Slater
2002). Noise that masks songs may also favor
modulation of amplitude, frequency, rhythm,
timbre, and call bandwidth (Lohr et al. 2003).
For example, Li le Greenbuls (Andropadus
virens) living in densely vegetated African
forests with relatively less low-frequency
noise were found to have songs with lower
minimal frequencies than populations living
nearby in grasslands with relatively more low-
frequency noise (Slabbekoorn and Smith 2002b,
Slabbekoorn 2004).
Human-created environmental noise has
changed considerably in volume, acoustic
structure, and global distribution as a result
of industrialization and urbanization. These
changes present evolutionarily novel acoustic
environments for many birds worldwide and
studies have only recently begun to address
the eff ects of anthropogenic noise on acoustic
signalers (see Slabbekorn and Peet 2003, Foote
et al. 2004, Ka i and Warren 2004, Leader et al.
2005, Sun and Narins 2005). Among the pos-
sible eff ects of noise is masking of songs by
similar noise frequencies, thereby reducing the
distance over which songs can be heard (i.e.,
the active space; see Lohr et al. 2003). Because
bird song generally serves to a ract mates and
repel territorial intruders, a reduction in the
active space of a song could reduce the fi tness
of signalers in noisier territories. For example,
studies in The Netherlands show that roadways
decrease songbird population densities (Reij nen
and Foppen 1994), and traffi c noise seems to be
largely responsible (Reij nen et al. 1995).
Most anthropogenic noise (e.g., lawn mow-
ers, airplanes, industry, and particularly auto
traffi c) occurs at relatively low frequencies
(roughly ≤3 kHz). Many bird songs overlap
these frequencies, yet they also may extend to
higher frequencies. Thus, another possible eff ect
of anthropogenic noise is an increase in pitch to
escape masking; Great Tits (Parus major) were
found to sing songs with higher minimum fre-
quencies when their territories were in areas of
louder anthropogenic noise (Slabbekoorn and
Peet 2003). Birds singing amid masking noise
may also increase the amplitude of their songs;
for example, territorial Common Nightingales
(Luscinia megarhynchos) were found to sing
louder in areas with more traffi c noise (Brumm
and Todt 2002, Brumm 2004). In laboratory stud-
ies, noise within the spectral region of Common
Nightingale songs was most eff ective in inducing
increased amplitude (Brumm and Todt 2002).
We studied Song Sparrows (Melospiza melodia
var. morphna). Song Sparrows occur over a large
area of North America, in both urban and rural
se ings. Individual males sing a repertoire of
songs, each made up of a series of notes and
trills whose frequency range (1,140–9,280 Hz in
our study population) partially overlaps the fre-
quencies of anthropogenic noise. To our knowl-
edge, this is the fi rst study of a North American
bird that tests the hypothesis that songs vary
in relation to anthropogenic noise. We tested
three predictions. First, those males occupying
territories with higher amplitudes of anthropo-
genic noise have songs with a higher minimum
frequency. Second, those males occupying ter-
ritories with higher anthropogenic noise exhibit
greater sound energy (amplitude) within the
upper-frequency portion of song relative to
the energy (amplitude) of the lower-frequency
portion of the song. Third, those males occupy-
ing territories with higher anthropogenic noise
have songs that do not diff er in their maximum
frequency, which is well above the dominant
frequency of anthropogenic noise.
Song Sparrows are year-round residents in
Portland, Oregon, where they begin territorial
singing around late February to early March
W  Y
[Auk, Vol. 123
(W. Wood and S. Yezerinac pers. obs.). Our
study area (~50 km
) in southeast Portland was
bounded to the north by Powell Boulevard, to
the south by Tacoma Street, to the west by the
Willame e River, and to the east by SE 162nd
Avenue. It encompassed many hundreds of
resident Song Sparrows, in habitats rang-
ing from urban parks and roadside verges to
residential yards. Individuals were selected for
recording solely on the basis of their singing
activity and accessibility as we walked along
sidewalks and paths; whenever a singing bird
was positively identifi ed by sight and sound,
we recorded it. The only exception occurred
when territories were within 10 m of each other,
making separation of individuals possibly
ambiguous. We recorded songs from 28 wild
male Song Sparrows between 19 March and 9
May 2004. Recordings were made between 0630
and 1604 hours PST (mean time of day = 0856
hours ± 106 min [SD]). Recordings were made
only when wind speeds were 2 on the Beaufort
Scale and precipitation was so light that it did
not create recording noise when falling on
the parabola. All song recordings were made
using a Marantz PMD-222 tape recorder with a
Sennheiser ME62 omnidirectional microphone
in a Telinga parabola (54-cm diameter). The
microphone and recorder were set to no fi lter
(fl at response). We a empted to record natural
song output from each individual for >3 min.
The prevailing ambient background noise
of each singing location was recorded immedi-
ately following song recording by placing the
omnidirectional microphone (removed from
the parabola) as close to the singing perch as
possible (10 m of collapsible pole were used
to elevate the microphone when necessary)
and recording for 3 min. The act of placing the
microphone near the perch caused the birds
to cease singing and depart, so interference by
singing birds was minimal. All noise recordings
were made using the same equipment as for the
song recordings. So that amplitudes could be
standardized across noise recordings, the tape
recorders gain was set to maximum (a constant)
and the input level was adjusted using a Shure
in-line a enuator (model no. A15A5; Shure,
Niles, Illinois) set at either –15 or –20 dB.
Recordings were digitized (16-bit, 44.1-
kHz sampling rate) using a Macintosh
G5 computer and AMADEUS so ware
(see Acknowledgments). Waveforms and
spec trograms (Hamming type; lter
band width = 699.4 Hz, smooth display style)
were measured using CANARY so ware (see
S M
Individual Song Sparrows generally sing
between 5 and 13 diff erent song types, cycling
through their diff erent song types and repeat-
ing one type for a number of minutes before
switching to the next (Arcese et al. 2002). Of the
28 bird recordings, 26 contained two or more
song types (mean = 3.2 ± 1.69 [SD]). We made
no eff ort to compare song types among indi-
viduals. Two songs from each individual were
selected at random for measurement of high
frequency, low frequency, frequency of greatest
amplitude, duration, and number of notes. The
same measurements (except number of notes)
were made for the buzz note within each song.
When more than one buzz note occurred in a
song, the buzz with the lower frequency was
measured. We anticipated that it may have
been more diffi cult to measure low frequency
in recordings with a lot of low-frequency back-
ground noise, but in practice this was not a
problem. Spectrograms of the two noisiest loca-
tions (Fig. 1) show that the lowest-frequency
notes sung by the birds are easily discernible
among the low-frequency noise. Measurements
of high frequency were perhaps the most dif-
cult to make, owing to the blurring of high-
frequency notes that results from the aspherical
spread of sound from low to high frequencies
(see Lohr et al. 2003). Lastly, songs were arbi-
trarily divided into low-frequency (1–4 kHz)
and high-frequency (4–9 kHz) ranges, and the
amplitude within each range was measured
using CANARY’s average intensity measure-
ment, which directly corresponds to sound
level and is measured in decibels. We calculated
the ratio of low-frequency amplitude to high-
frequency amplitude for each song. This ratio
can be compared across recordings made at dif-
ferent amplifi cation levels and is not susceptible
to mismeasurement caused by noise obscuring
notes on the spectrogram. In fact, this ratio mea-
surement is conservative with respect to our
hypothesis, because inclusion of low-frequency
noise in the amplitude measurement of the song
would tend to skew the ratio in the direction
opposite to that predicted by our hypothesis.
Song and NoiseJuly 2006]
N M
The noise recordings were made with stan-
dardized amplifi cation levels (as described
above). Calibration tones of known amplitude
were also recorded. Combined, these allowed
us to make commensurate measures of noise
amplitude at diff erent singing locations. Briefl y,
the calibration tone was produced with a Radio
Shack 273-059 piezo buzzer. Measurement with
a Radio Shack 33-2050 sound level meter (set to
A” weighting and fast response and used only
for initial calibration) at 60 cm indicated that the
root mean square (RMS) decibels of the calibra-
tion tone was 70 dB in relation to atmospheric
pressure. The calibration tone was recorded
60 cm from the omnidirectional microphone.
We used CANARY and the protocols outlined
in the users manual (Charif et al. 1995) to create
a calibration document (default “Air” se ings)
that contained three separate one-second dura-
tion recordings of the calibration tone. Applying
the corresponding calibration fi le to each noise
recording to be measured allowed measure-
ment of sound levels using CANARY’s average
intensity measurement. Sound intensity in three
frequency ranges was measured: pertinent fre-
quencies (1–9 kHz), which correspond to the
hearing range of the Song Sparrow (Okanoya
and Dooling 1988), low frequencies (1–4 kHz),
and high frequencies (4–9 kHz). Division of the
frequency range at the 4-kHz mark was chosen
because this is the middle of the frequency range
exhibited by most Song Sparrow songs.
F. 1. The lowest-frequency notes sung are easily discernible in spectrograms of Song Sparrow
songs from recordings with (A) the most low-frequency background noise and (B) the second-most
low-frequency background noise encountered in the present study.
W  Y
[Auk, Vol. 123
A B N
Total ambient background noise (0–22 kHz)
at singing perches varied from 54.8 to 71.3 dB
(mean ± SD: 61.5 ± 4.77 dB). Noise in the fre-
quency range of Song Sparrow songs (1–9 kHz)
varied from 32.4 to 59.7 dB (46.2 ± 7.17 dB),
noise in the low range (1–4 kHz) varied from
31.5 to 59.7 dB (45.6 ± 7.4 dB), and noise in
the high range (4–9 kHz) varied from 21.7 to
50.6 dB (34.8 ± 6.9 dB). Variation among sing-
ing perches in the level of pertinent background
noise (1–9 kHz) was almost perfectly corre-
lated with that for low-frequency background
noise (1–4 kHz; r = 0.993, P < 0.0001, n = 28),
refl ecting the fact that most of the noise in the
pertinent noise spectrum was actually in the
low-frequency range.
S A N
The minimum frequency of songs was
higher when the amplitude of low-frequency
background noise was greater (r = 0.65, P =
0.0002, n = 28; Fig. 2). The relationship between
minimum frequency of songs and pertinent
background noise was weaker and also sig-
nifi cant (r
= 0.59, P = 0.0008, n = 28). Minimum
frequency of songs was not correlated with the
amplitude of high-frequency noise (r = –0.045,
P = 0.82, n = 28).
The amplitude of the low-frequency portion
(1–4 kHz) of songs was lower than that of the
high-frequency portion (4–9 kHz) when low-
frequency background noise was greater (r =
0.40, P = 0.03, n = 28; Fig. 3). That is, at sites
with louder low-frequency background noise,
songs had relatively less energy in the lower
frequency range than in the higher-frequency
portion. This a more conservative test of diff er-
ences in song, because noise occurring primar-
ily at low frequencies would have contributed
to the measurement of the low-frequency song
As expected, there was no relationship
between the high frequency of songs and the
amplitude of low-frequency background noise
(r = 0.08, P = 0.67, n = 28). In fact, none of the
other song characters we measured (high
frequency of song, frequency at maximum
amplitude, high frequency of buzz note, low
frequency of buzz note, frequency of buzz note
at maximum amplitude, duration of buzz note,
number of notes) was signifi cantly related to
the measures of noise. The strongest relation-
ship was the tendency for the number of notes
of a song to decrease with the amplitude of total
(0–22 kHz) noise (r = –0.29, P = 0.13, n = 28).
Song characters that were associated with
lower frequencies (low frequency of song, ratio
of the amplitude of the low frequencies of song
to the amplitude of the high frequencies of
F. 3. The ratio of the amplitude of the
low-frequency portion (1–4 kHz) of songs to
the amplitude of the high-frequency portion
(4–9 kHz) of songs was negatively related to the
amplitude of low-frequency background noise
among territorial Song Sparrows recorded in
Portland, Oregon (r = –0.40, P = 0.03, n = 28).
F. 2. The lowest frequency of songs is posi-
tively related to the amplitude of low frequency
background noise among territorial Song
Sparrows recorded in Portland, Oregon (r =
0.65, P = 0.0002, n = 28).
Song and NoiseJuly 2006]
song) varied signifi cantly with the amount of
low-frequency noise. Song characters that were
not associated with lower frequencies (high
frequency of song, frequency at maximum
amplitude, trill characteristics) did not vary
signifi cantly with background noise.
Song Sparrows singing at noisier locations had
higher-frequency low notes and had relatively
less energy (amplitude) in the low-frequency
range of their songs (1–4 kHz). Combined, these
results clearly indicate that Song Sparrow songs
varied in their low frequency in relation to lev-
els of urban noise. None of the other song com-
ponents measured (high frequency, frequency
at maximum amplitude, number of notes,
frequency of buzz note) showed a signifi cant
correlation with background noise. Background
noise in our study area was predominantly at
low frequencies, so masking of the middle- and
upper-frequency portions of song was minimal.
Perhaps the most surprising pa ern is that
songs diff ered only in those aspects that were
masked by the prevailing noise spectrum. It
appears that Song Sparrows modifi ed the low
frequency of their songs while keeping other
parts of song remarkably constant.
The same overall result was evident in a study
of Great Tits in The Netherlands (Slabbekoorn
and Peet 2003; H. Slabbekoorn pers. comm.).
By contrast, a study of vocal modifi cations in
response to road noise in the California ground
squirrel (Spermophilus beecheyi) found that the
low frequency of ground squirrel calls remained
unchanged. Average frequency, high frequency,
and frequency at maximum amplitude, how-
ever, were all of higher frequency at noisy sites
(Rabin et al. 2003). It will be interesting to see
whether this pa ern is matched in other taxa,
because it bears some relation to mechanisms of
sound production.
Male Song Sparrows have good reason to
maintain clear song transmission—their repro-
ductive success may depend on it. Song plays
a role in male–male confl icts, functioning to
maintain territories and repel intruding males
(Nowicki et al. 1998). Female mate choice in
Song Sparrows is also heavily infl uenced by
male song. For instance, the quality of male
song-learning has been positively correlated
with female preferences (Nowicki et al. 2002),
as has song repertoire size (Searcy 1984, Reid et
al. 2004) and geographically dependent dialec-
tic variation (Searcy et al. 2002). The proximate
pressures are thus many and intimately coupled
with sexual selection; the ontogenetic mecha-
nisms acting to maintain the songs, however,
are not so obvious.
There are several possible paths by which the
observed shi in frequency may have arisen.
First, individuals may have the ability to facul-
tatively modify their songs between or during
song bouts according to the prevailing noise.
Such an inherent ability would be analogous to
the Lombard eff ect, a refl exive increase in ampli-
tude of vocalization in response to masking
noise (Cherry 1966, Cynx et al. 1998, Lombard
1911, Manabe et al. 1998), and may have evolved
to deal with environmental noise from sources
such as wind or waves. Song Sparrows have a
repertoire of 5–13 songs that diff er in frequency
and which they sing with variety (Arcese et al.
2002), so it is possible that individuals choose to
sing the song(s) from their repertoires that are
not as masked by the prevailing noise. They may
also be able to change the frequency at which
they sing particular song types. Testing these
hypotheses will require prolonged recordings
of individuals under diff erent noise levels. Our
preliminary data contrasting the same roadside
individuals recorded at times of peak and low
traffi c ow are inconclusive (W. Wood and S.
Yezerinac unpubl. data).
A second possibility is that individuals
undergo a process of ontogenetic change
resulting in a song repertoire that matches
the noisiness of their territory. Song Sparrows
are year-round residents in our study area
and show high levels of territory fi delity (see
Nordby et al. 1999). Moreover, neurological
studies have shown that each spring, male Song
Sparrows undergo a partial renewal of brain
regions involved in song learning and pro-
duction (Tramontin and Brenowitz 1999, 2000;
Thompson and Brenowitz 2005), and behavioral
studies show associated subtle changes in song
(Smith et al. 1997; but see Nordby et al. 2002).
Further examination of the details of these song
changes can test the intriguing hypothesis that
Song Sparrows are able to tailor their song pro-
duction according to the prevailing noise spec-
trum they experience on their territories each
spring. The feedback mechanism could involve
males hearing the noise spectrum on their
W  Y
[Auk, Vol. 123
territory or behavioral reinforcement in the
form of diff erential success of songs in a ract-
ing females or repelling unwanted males (also
see Beecher et al. 1994). Additionally, selective
a rition, whereby individuals learn more songs
than they will eventually sing and selectively
lose some of them over the course of their
second year (Nelson and Marler 1994), may
be aff ected by noise. Selective a rition in Song
Sparrows is partially determined by matching
songs of neighbors, but not all of the variation
in a rition has been explained (Nordby et al.
1999), and noise on the territory where a male
se les may shape his repertoire.
Other ontogenetic infl uences of noise on song
may occur early in life, during the critical juve-
nile period of song learning (Marler and Peters
1987; Nowicki et al. 1999; Nordby et al. 2001,
2002). Juveniles living in nosier areas may not
hear, and thus not learn to sing, the low-fre-
quency notes of the previous generation. Song
Sparrows also may listen to their own calls dur-
ing the crystallization period of song learning
and make changes if the notes sound masked.
These infl uences, however, would not necessar-
ily produce the patchwork pa ern of matching
across territories between male song and noise,
unless males also selectively disperse to or retain
territories that match the acoustic environments
in which they were raised. Although it is known
that Song Sparrows in other parts of the Pacifi c
Northwest establish territories near where they
learn to sing (Arcese 1987, 1989), it is not yet
clear to us whether individuals in our study
area experience similar noise levels as juveniles
and as adults. Nevertheless, these mechanisms
also suggest that urban populations may shi
their overall average song frequency, as com-
pared with nearby quieter populations, because
of ontogenetic infl uences on early song learn-
ing. Testing of this possibility by comparing
populations for song frequency is potentially
confounded by geographic variation between
populations caused by other evolutionary
Finally, if songs of diff erent frequency dif-
fer in their eff ectiveness for communication
depending on noise, selection may be acting on
existing genetic variation for song frequency.
Again, this mechanism cannot easily account
for the observed patchwork of song frequencies
across local territories but should be considered
Although higher-frequency songs may
im prove communicative effi cacy for Song
Sparrows in noisy environments, this may come
at a cost. Although we did not measure total
amplitude of song, studies of the Lombard eff ect
in other song birds indicate that birds generally
sing more loudly in response to noise, with noise
in the frequency range of their songs eliciting
the greatest responses (Manabe et al. 1998,
Brumm and Todt 2002). In noisier locations,
Song Sparrows may sing more loudly, which
has been shown to increase rates of oxygen con-
sumption and energy expenditure in songbirds
(Oberweger and Goller 2001). Peak sensitivity of
Song Sparrow hearing occurs ~2 kHz (Okanoya
and Dooling 1988), so the eff ect of the observed
frequency shi (which occurred ~2 kHz) on sig-
nal reception must also be considered. Thus, pos-
sible eff ects of vocal modifi cations in response to
anthropogenic noise in Song Sparrows range
from decreased individual health to divergence
of song phenotypes between urban and rural
Aside from the acoustic environment, urban
areas are distinct in many ways, including species
composition (Clergeau et al. 1998, 2001). Only
certain species, such as the Song Sparrow, are
evidently able to adapt and maintain their popu-
lations in urban environments like Portland (see
Hennings and Edge 2003). Whether or not these
populations diverge phenotypically from exur-
ban populations may be mediated by song char-
acters and their eff ect on mating; furthermore,
female Song Sparrows have been shown to dis-
criminate against songs from populations >34 km
distant (Searcy et al. 2002), and the possibility of
speciation between urban and rural populations
of Song Sparrows should not be overlooked.
We appreciate the indulgence of residents of
the neighborhoods in which we recorded and
the constructive comments on the paper pro-
vided by B. Montgomerie, A. Du y, students
in Bio 431-Ecology, Behavior and Conservation,
and two anonymous reviewers. Equipment
was purchased with a National Academy of
Sciences Undergraduate Research Grant from
Reed College. AMADEUS so ware is available
at www.hairerso .com. CANARY so ware
is available at
Song and NoiseJuly 2006]
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... However, urban noise often extends beyond the described main frequency band of 2 kHz and thus one should not entirely discount the possibility that the higher frequency Noisy miner calls still overlapped spectrally to some extent with background urban noise. Facultative shifts in minimum frequency of songs have been identified in several songbirds [14,15,18,29,30] and, more recently, in calls in urban environments [18,31]. In these studies, birds were found to increase the lower frequency of signals above the main frequency band of anthropogenic noise and, in so doing, reduce vocal masking, although research suggests that these types of adjustments are not always sufficient to counter the effects of anthropogenic disturbance [32]. ...
... There was no discernable difference between urban and rural Noisy miners in dominant frequency of any of the calls measured. Shifts in dominant frequency have been identified in other birds [14,17,31] and frogs [34] inhabiting noisy environments. Notably, a meta-analysis by Roca et al. [38] found, from 36 studies compared, that birds typically demonstrated facultative shifts in dominant frequencies in the presence of anthropogenic noise, whereas anuran species mostly did not. ...
... Increasing the duration of signals has been shown to improve the detectability of sounds in white noise [49] and several studies have found facultative shifts in call duration in birds living in noisy conditions in urban habitats [1,15]. In contrast, research on urban Song sparrows [14] and Dark-eyed juncos, Junco hyemalis [30], found that individuals did not change trill duration where both species showed adjustments to the frequency (kHz) of songs under noisy conditions. We found no differences in call duration between urban and rural Noisy miners, apart from the second note of the post-feeding call. ...
Full-text available
Urban environments are characteristically noisy and this can pose a challenge for animals that communicate acoustically. Although evidence suggests that some birds can make acoustic adjustments that preclude masking of their signals in high-disturbance environments such as cities, studies to date have tended to focus on acoustic signals important in mate attraction (e.g., songs). Far less attention has been given to the impact of urban noise on other kinds of calls. To redress this, we compared a range of different vocalizations (encompassing alarm calls, begging calls and parent response calls) among urban and rural individuals of a successful Australian 'urban adapter', the Noisy miner, Manorina melanocephala. We found that urban miners had significantly higher minimum sound frequencies for calls with low base-frequencies (<2 kHz); however, calls with base-frequencies 'naturally' above the main frequency range of urban noise (>2 kHz) had the same minimum frequency in urban and rural birds. Dominant frequency and call duration did not differ between urban and rural individuals. Although urban Noisy miners exhibited differences from rural individuals in the minimum frequency of calls, this shift was not large enough to avoid masking from low-frequency, anthropogenic noise. Nevertheless, our findings suggest that the calls of Noisy miners may be naturally well suited to being heard in noisy urban environments by having (a) dominant frequencies higher than low-level, anthropogenic noise and (b) several important call-types with frequencies above the main frequency range associated with urban noise.
... These and other findings suggest that birds are modifying their vocalizations as a result of noise in order to communicate with conspecifics 57,58 . However, how are the receivers, both conspecific and heterospecific, of these modified signals perceiving these modified vocalizations? ...
Full-text available
When anthropogenic noise occurs simultaneously with an acoustic signal or cue, it can be difficult for an animal to interpret the information encoded within vocalizations. However, limited research has focused on how anthropogenic noise affects the identification of acoustic communication signals. In songbirds, research has also shown that black-capped chickadees (Poecile atricapillus) will shift the pitch and change the frequency at which they sing in the presence of anthropogenic, and experimental noise. Black-capped chickadees produce several vocalizations; their fee-bee song is used for mate attraction and territorial defence, and contains information about dominance hierarchy and native geographic location. Previously, we demonstrated that black-capped chickadees can discriminate between individual female chickadees via their fee-bee songs. Here we used an operant discrimination go/no-go paradigm to discern whether the ability to discriminate between individual female chickadees by their song would be impacted by differing levels of anthropogenic noise. Following discrimination training, two levels of anthropogenic noise (low: 40 dB SPL; high: 75 dB SPL) were played with stimuli to determine how anthropogenic noise would impact discrimination. Results showed that even with low-level noise (40 dB SPL) performance decreased and high-level (75 dB SPL) noise was increasingly detrimental to discrimination. We learned that perception of fee-bee songs does change in the presence of anthropogenic noise such that birds take significantly longer to learn to discriminate between females, but birds were able to generalize responding after learning the discrimination. These results add to the growing literature underscoring the impact of human-made noise on avian wildlife, specifically the impact on perception of auditory signals.
... The song sparrow and gray catbird are two of the more abundant species reported in developed counties within the study region (observed on 48.6% and 47.3% of ebird lists submitted May-June in all years for Wayne, Kent, and Kalamazoo counties). Rapid temporal shifts in vocalization rates combined with frequency shifting (Wood and Yezerinac, 2006;Dowling et al., 2012) may underlie the urban success observed in these species. The field sparrow and chipping sparrow are less common in the region's developed counties (11.6% and 29.7% of lists respectively). ...
Full-text available
Mounting evidence suggests that anthropogenic noise neg-atively impacts many wildlife species, including songbirds. One mechanism by which noise affects songbirds may be through acoustic obstruction to their systems of vocal communication. However, many species increase the amplitude or pitch of their vocalizations, which may partially mitigate the impact of high noise levels. When the amplitude of anthropogenic noise varies over time, such as near a moderate-use highway, short gaps between noise events may also provide an important oppor- tunity for communication. But, whether songbirds adjust vocalization rates rapidly to avoid overlap with noise is unknown for most species. We used acoustic playback to expose song- birds to simulated road noise during the dawn chorus in oth- erwise quiet habitats. We measured vocalization rates under ambient conditions and during quiet gaps embedded within playback of road noise to assess whether a community of songbirds, and nineteen individual species, vocalize more reg- ularly during noise gaps. There were no significant differences in community-wide acoustic output. Species-specific analysis revealed that only four species altered their vocal rates during quiet gaps in noise, but that the direction of the effect varied by species. Point count results revealed that birds generally remained on site for the duration of the experiment, suggesting that abandonment of noisy locations was unlikely to confound our results. In sum, increasing vocal output during short gaps in noise occurred in only a handful of species, perhaps con- tributing to the limited number of species that are found within noisy habitats.
... With anthropogenic habitat alteration now affecting most biomes in a variety of ways (Ellis & Ramankutty, 2008), one of the more poorly understood consequences of such alteration is the effect of the introduction of anthropogenic noise, such as traffic noise, on acoustically communicating animals. Some species of birds have been shown to avoid habitats near roads (Forman & Alexander, 1998) or to alter spectral or temporal properties of calls when presented with anthropogenic noise (Slabbekoorn & Peet, 2003; Slabbekoorn & den Boer-Visser, 2006; Wood & Yezerinac, 2006). Although frogs are among the most vocal vertebrates (Narins, 1982 ), only recently have they become a focus for studies of behavioural responses to exogenous noise. ...
... The noise 85 stimulus was played from a second speaker (Pignose Model No. 7-100R) placed on the ground directly 86 below the mount, face up, at 75 dB SPL measured at 1 m. These levels create an ambient noise range 87 between 60 to 70 dB SPL within 5m of the mount which corresponds to noise levels on territories near 88 highways [32]. We placed this speaker for both noise and control trials, but only turned it on in noise 89 trials. ...
Full-text available
Although the effects of anthropogenic noise on animal communication have been studied widely, most research on the effect of noise in communication has been on communication in a single modality. Consequently, how multimodal communication is affected by anthropogenic noise is relatively poorly understood. Here we ask whether song sparrows ( Melospiza melodia ) show evidence of plasticity in response to noise in two aggressive signals in acoustic and visual modalities. We test two hypotheses: (1) that song sparrows will shift signaling effort to the visual modality (the multi-modal shift hypothesis), and (2) that they will increase redundancy of their multi-modal signaling (the back-up hypothesis). We presented male song sparrows with song playback and a taxidermic mount with or without a low-frequency acoustic noise from a nearby speaker. We found that males did not switch their signaling effort to visual modality (i.e., wing waves) in response to the noise. However, the correlation between warbled soft songs and wing waves increased in the noise treatment, i.e. signals became more redundant. These results suggest that when faced with anthropogenic noise, song sparrows can increase redundancy of their multi-modal signals, which may aid in robustness of the communication system.
Anthropogenic noise (≤ 3 kHz) can affect key features of birds’ acoustic communication via two different processes: (1) song‐learning, because songbirds need to hear themselves and other birds to crystallize their song, and (2) avoidance of song elements that overlap with anthropogenic noise. In this study we tested whether anthropogenic noise reduces the number of song elements in the repertoire of House Wren Troglodytes aedon , an urban species. Additionally, we tested whether the proportion of high‐frequency elements (i.e. elements where the minimum frequency is above 3 kHz) is related to anthropogenic noise levels, and how the frequencies and duration of shared elements between males change with different levels of anthropogenic noise. We recorded 29 House Wren males exposed to different anthropogenic noise levels (36.50–79.50 dB) during two consecutive breeding seasons from four locations. We recorded each male on 2 days during each season continuously for 50 min (we collected 104 h of recordings) and measured anthropogenic noise levels every 10 min inside each male territory during the recording period. In general, individuals inhabiting noisier territories had smaller repertoires. However, only in two locations with anthropogenic noise levels between 38.60 and 79.50 dB did males inhabiting noisier territories have smaller repertoires. In the other two locations with lower anthropogenic noise (36.50–66.50 dB), the anthropogenic noise inside each territory was not related to the repertoire size. Individuals inhabiting the noisiest location showed a tendency to include more high‐frequency elements in their songs. In 26% of the elements, the anthropogenic noise affected their frequency features. Our results showed that not all House Wrens inhabiting urban environments modify their songs at the highest level of organization (i.e. repertoire) to reduce the masking effect of anthropogenic noise on acoustic communication.
The noise filter hypothesis predicts that species using higher sound frequencies should be more tolerant of noise pollution, because anthropogenic noise is more intense at low frequencies. Recent work analysed continental‐scale data on anthropogenic noise across the USA and found that passerine species inhabiting more noise‐polluted areas do not have higher peak song frequency but have more complex songs. However, this metric of song complexity is of ambiguous interpretation, because it can indicate either diverse syllables or a larger frequency bandwidth. In the latter case, the finding would support the noise filter hypothesis, because larger frequency bandwidths mean that more sound energy spreads to frequencies that are less masked by anthropogenic noise. We reanalysed how passerine song predicts exposure to noise using a more thorough dataset of acoustic song measurements, and showed that it is large frequency bandwidths, rather than diverse syllables, that predict the exposure of species to noise pollution. Given that larger bandwidths often encompass higher maximum frequencies, which are less masked by anthropogenic noise, our result suggests that tolerance to noise pollution might depend mostly on having the high‐frequency parts of song little masked by noise, thus preventing acoustic communication from going entirely unnoticed at long distances.
Acoustic noise from automobile traffic impedes communication between signaling animals. To overcome the acoustic interference imposed by anthropogenic noise, species across taxa adjust their signaling behavior to increase signal saliency. As most of the spectral energy of anthropogenic noise is concentrated at low acoustic frequencies, species with lower frequency signals are expected to be more affected. Thus, species with low‐frequency signals are under stronger pressure to adjust their signaling behaviors to avoid auditory masking than species with higher frequency signals. Similarly, for a species with multiple types of signals that differ in spectral characteristics, different signal types are expected to be differentially masked. We investigate how the different call types of a Japanese stream breeding treefrog (Buergeria japonica) are affected by automobile traffic noise. Male B. japonica produce two call types that differ in their spectral elements, a Type I call with lower dominant frequency and a Type II call with higher dominant frequency. In response to acoustic playbacks of traffic noise, B. japonica reduced the duration of their Type I calls, but not Type II calls. In addition, B. japonica increased the call effort of their Type I calls and decreased the call effort of their Type II calls. This result contrasts with prior studies in other taxa, which suggest that signalers may switch to higher frequency signal types in response to traffic noise. Furthermore, the increase in Type I call effort was only a short‐term response to noise, while reduced Type II call effort persisted after the playbacks had ended. Overall, such differential effects on signal types suggest that some social functions will be disrupted more than others. By considering the effects of anthropogenic noise across multiple signal types, these results provide a more in‐depth understanding of the behavioral impacts of anthropogenic noise within a species.
Although the effects of anthropogenic noise on animal communication have been studied widely, most research on the effect of noise in communication has focused on signals in a single modality. Consequently, how multi-modal communication is affected by anthropogenic noise is relatively poorly understood. Here, we ask whether song sparrows (Melospiza melodia) show evidence of plasticity in response to noise in two aggressive signals in acoustic and visual modalities. We test two hypotheses: (i) that song sparrows will shift signalling effort to the visual modality (the multi-modal shift hypothesis) and (ii) that they will increase redundancy of their multi-modal signalling (the back-up signal hypothesis). We presented male song sparrows with song playback and a taxidermic mount with or without a low-frequency acoustic noise from a nearby speaker. We found that males did not switch their signalling effort to visual modality (i.e. wing waves) in response to the noise. However, the correlation between warbled soft songs and wing waves increased in the noise treatment, i.e. signals became more redundant. These results suggest that when faced with anthropogenic noise, song sparrows can increase the redundancy of their multi-modal signals, which may aid in the robustness of the communication system.
Cities exert strong selective pressures on plants and animals to adapt to urban life. They provide a unique testing ground for studying evolution in action.
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Biologically important acoustic signals must be transmitted from a signaler to a receiver. Over distance, however, sounds may undergo modification through attenuation, degradation, and masking. Recent anthropogenic habitat modification occurring in many places—in urban habitats, in particular—has rapidly changed local topography and atmospheric conditions and generated new patterns of noise that are likely to interfere with communicative signals. As part of a study of microgeographic song dialects in an urban population of Orange-tufted Sunbirds (Nectarinia osea) in Israel, we examined the environmental influences on song transmission and reception in a rapidly developing human-altered environment. We examined the physical properties of the two dialect song types, which exhibit a large difference of 2–3 kHz in the maximum frequency of the trill, using sound transmission measurements to test how both song types propagate through a highly obstructed habitat of buildings and vegetation. Additionally, we examined how ambient noise—in particular, low-frequency noise arising mainly from automobile traffic—affects the transmission of both dialect songs. Finally, using song playback, we investigated the consequences of sound degradation on dialect recognition and discrimination by sunbirds. The dialect containing higher frequencies in the trill was found to undergo severe frequency-dependent attenuation, in which the maximum frequency of the trill notes drops by >2 kHz over a distance of 70–100 m (less than two territories away). Also, the possibility that the use of higher frequencies in that dialect group's song is intended to overcome masking by urban ambient noise, which is concentrated mainly in lower frequencies, was not supported by our findings. Males singing the high dialect responded differently to playbacks of an intact and an attenuated form of their dialect song. Taken together, our results suggest that the dialect containing higher frequencies in the trill may be unsuitable for effective long-range transmission through this particular sunbird habitat. Propiedades Acústicas de Dos Dialectos del Canto Urbano de Nectarinia osea
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We compared the avifauna in two cities, Quebec (Canada) and Rennes (France), in order to define general responses of wildlife in an urban ecosystem. These cities have a similar urban structure that permits investigation along an urbanization gradient from downtown to rural residential areas. However, they are in opposite temperate climate and imbedded in a forested and an agricultural landscape, respectively. Plots ranging from 10 to 20 ha were surveyed in winter and spring by recording all birds seen or heard. Most plots could be located along a gradient according to proportions of vegetated open space. Both the Shannon-Wiener and Simpson indices of diversity indicated a pattern of increasing diversity from most to least urbanized areas in spring. Winter species diversity and richness was low in Quebec compared to Rennes, reflecting the much harsher winter conditions in Quebec. Breeding densities of House Sparrows (Passer domesticus) and European Starlings (Sturnus vulgaris) were quite similar in Quebec and Rennes, as were densities of European Blackbirds (Turdus merula) and its ecological equivalent in Quebec, the American Robin (Turdus migratorius). The type of surrounding landscape can not explain the Variation of species numbers within the city. If we examine the urban environment as a new ecological system rather than a degraded environment, we can regroup birds in two major species groups: the omnivorous species adapted to the urban environment and its particular food resources such as garbage and the species that find, in the urban environment, resources which they normally exploit in their usual habitat.
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Conservation biology and comparative psychology rarely intersect, in part because conservation biology typically emphasizes populations whereas comparative psychology concentrates on individual organisms. However, both fields could benefit from their integration. Conservation biology can profit from an enhanced understanding of individual-level impacts of habitat alteration and the resulting implications for conservation mitigation strategies. Comparative psychology can gain from increased attention to the mechanisms of adjustment used by organisms to "in vivo experiments" created by anthropogenic change. In this paper, we describe a conceptual framework useful for applying our understanding of animal communication to conservation biology. We then review studies of animal communication with conservation implications, and report our own preliminary work that demonstrates our framework in action. Copyright Information:
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Most studies of song learning have been conducted in the laboratory, and thus little is known about how song learning is affected by ecological variables in nature. Taking an ecological perspective, we studied song learning and territory establishment in a sedentary population of song sparrows (Melospiza melodia). We examined the song repertoires of an entire cohort of males (41 subjects) hatched in 1992 and compared them to those of potential song tutors (adults who were present in the young birds' first year). We found that a young bird learns songs from multiple tutors who were neighbors in his first year and usually establishes a territory among or near these tutors. The degree to which tutors influenced the repertoires of the young birds varied greatly. Adult males who survived into 1993 tutored more songs than those who did not survive, supporting the hypothesis that a young male's repertoire is influenced by social interactions with adults continuing beyond the classical sensitive period of the natal summer. The final repertoire of a young bird in most cases was weighted toward one of his tutors with whom he continued to interact, as an immediate neighbor, into his first spring. We found no correlations between potential measures of male quality or vigor and degree of tutor influence. Key words: bird song, male quality, Melospiza melodia, song learning, song repertoire, song sparrow, territory establishment. (Behav Ecol 10:287-297 (1999))
In 1999, we surveyed breeding bird and plant communities along 54 streams in the Portland, Oregon, metropolitan region to link bird community metrics with structural and spatial characteristics of urban riparian areas. Canonical correspondence analysis produced two explanatory axes relating to vegetation and road density. Total and non-native bird abundance was higher in narrow forests. Native bird abundance was greater in narrow forests surrounded by undeveloped lands; native species richness and diversity were greater in less-developed areas. Native resident and short-distance-migrant abundance was higher in narrow forests, and diversity was positively associated with developed lands. Neotropical migrant abundance, richness, and diversity were greater in open-canopied areas with fewer roads. We examined spatial relationships by regressing bird variables on satellite-derived forest canopy cover, area of undeveloped lands, and street density in a series of 50-m buffers within a 500-m radius around study sites. Non-native bird abundance decreased with increasing canopy cover within 450 m, but most other relationships were strongest at smaller scales (50–100 m). Our results suggest that increasing urban canopy cover is the most valuable land management action for conserving native breeding birds. A hierarchical scheme for Neotropical migrant conservation might include increasing forest canopy within 450 m of streams to control non-native species and cowbirds; reducing street density within a 100-m radius of streams; and conserving or planting onsite native trees and shrubs. Estructura de Comunidades Riparias de Aves en Portland, Oregon: Hábitat, Urbanización y Patrones de Escala Espacial Resumen. Censamos las comunidades de aves reproductivas y plantas a lo largo de 54 arroyos en el área metropolitana de Portland, Oregon en 1999 para conectar medidas de comunidades de aves con características estructurales y espaciales de zonas riparias urbanas. Análisis de correspondencia canónica produjeron dos ejes explicativos relacionados con la vegetación y la densidad de carreteras. La abundancia total de aves y la de aves no nativas fueron mayores en bosques estrechos. La abundancia de aves nativas fue mayor en bosques estrechos rodeados por terrenos rurales y la riqueza y diversidad de especies fueron mayores en áreas menos desarrolladas. La abundancia de residentes nativas y migratorias de corta distancia fue mayor en bosques estrechos y su diversidad estuvo asociada positivamente con terrenos desarrollados. La abundancia, riqueza y diversidad de las migratorias neotropicales fueron mayores en áreas de dosel abierto y con pocas carreteras. Examinamos las relaciones espaciales mediante regresiones entre variables de aves y la cobertura del dosel derivada de imágenes satelitales, el área de terrenos sin desarrollar y la densidad de calles en una serie de áreas de 50 m de ancho en un radio de 500 m alrededor de los sitios de estudio. La abundancia de aves no nativas disminuyó con aumentos en la cobertura del dosel hasta 450 m, pero la mayoría de las demás relaciones fueron más fuertes a escalas menores (50–100 m). Nuestros resultados sugieren que el incremento de la cobertura del dosel en áreas urbanas es la estrategia de manejo más valiosa para conservar las aves nativas que se reproducen en el área. Un esquema jerárquico para la conservación de las migratorias neotropicales podría incluir aumentar la cobertura de bosque a menos de 450 m de los arroyos para controlar a las especies no nativas y a los Molothrus, reducir la densidad de calles dentro de un radio de 100 m alrededor de los arroyos y conservar o plantar árboles y arbustos nativos.
Whether geographic variation in signals actually affects communication between individuals depends on whether discriminable differences in signals occur over distances that individuals move in their lifetimes. We measure the ability of song sparrows (Melospiza melodia) to discriminate foreign from local songs using foreign songs recorded at a series of increasing distances and compare the results with previous measurements of dispersal distances. We test discrimination in males using playback of songs on territories and measuring approach and in females using playback to estradiol‐treated captives and measuring courtship display. Females fail to discriminate against foreign songs recorded at 18 km but do discriminate against foreign songs recorded at 34, 68, 135, and 540 km. Males fail to discriminate against foreign songs recorded at 18, 34, 68, 135, and 270 km but do discriminate against foreign songs from 540 km. Females are more discriminating, but even they do not discriminate at a distance three times the root‐mean‐square dispersal distance, as estimated from mtDNA variation. We suggest that female preference for local songs benefits females not because it allows them to reject foreign males but because accurate production of local song serves as a test of song‐learning ability.
The voices of birds have always been a source of fascination. Nature's Music brings together some of the world's experts on birdsong, to review the advances that have taken place in our understanding of how and why birds sing, what their songs and calls mean, and how they have evolved. All contributors have strived to speak, not only to fellow experts, but also to the general reader. The result is a book of readable science, richly illustrated with recordings and pictures of the sounds of birds. Bird song is much more than just one behaviour of a single, particular group of organisms. It is a model for the study of a wide variety of animal behaviour systems, ecological, evolutionary and neurobiological. Bird song sits at the intersection of breeding, social and cognitive behaviour and ecology. As such interest in this book will extend far beyond the purely ornithological - to behavioural ecologists psychologists and neurobiologists of all kinds.
Abstract We examined barriers to gene flow in a hybrid zone of two subspecies of the song sparrow (Melospiza melodia). We focused on how mating signals and mate choice changed along an environmental gradient and gathered data on the morphology, genetics, ecology, and behavior across the zone. Melospiza m. heermanni of the Pacific slope of California and M. m. fallax of the Sonoran Desert, each distinct in plumage, meet across a steep environmental gradient in southeastern California. Although both subspecies occur in riparian habitat, their occupied habitat differs structurally, the former subspecies occurring in areas with denser understory and greater vertical heterogeneity. Song elements varied concomitantly, as predicted by the acoustic adaptation hypothesis, with heermanni having lower-pitched, more widely spaced elements. Females of both subspecies responded more strongly to homotypic than heterotypic song, and addition of subspecific plumage cues increased response if song was homotypic but not if heterotypic. Females thus assess multiple male traits, weighing song more heavily. Males of both subspecies showed significantly greater agonistic response to homotypic song. Microsatellite variation is correlated significantly with plumage variation across the zone and suggests limited gene flow between the taxa. The association of song and plumage with the environment and in turn with assortative mating suggests a means by which reproductive isolation may evolve or be maintained in hybrid zones.