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dVideo=725&tipus=1 boreal owl
Pygmy Owl (Glaucidium passerinum) hooting
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Bird Vocalizations 1
JodyLee Estrada Duek, Ph.D.
With assistance from Dr. Gary Ritchison
Birds produce a variety of sounds
• to communicate with flock members, mates (or potential mates),
neighbors, & family members. These sounds vary from short,
simple call notes (and short, simple songs like those of Henslow's
Sparrows) . . . top
(with an occasional 'buzzy' song of a Grasshopper Sparrow in the background)
• . . . to surprisingly long, complex songs (e.g., the Superb Lyrebird
with David Attenborough).
• Sometimes birds generate sounds by using substrates (like
woodpeckers) or special feathers (like American Woodcock) or
special wings (like manakins).
• Red-capped Manakin (Pipra mentalis) using its wings to generate
• Male Anna's Hummingbirds use their tail feathers to generate
• Most sounds, however, are produced by the avian vocal organ, the
• Common loon
• The syrinx is located at the point where the trachea branches into the two
primary bronchi. According to one model of syrinx function, sound is
generated when:
• contraction of muscles (thoracic & abdominal) force air from air sacs
through the bronchi & syrinx
• the air molecules vibrate as they pass through the narrow passageways
between the external labia & the internal tympaniform membranes (or, as
in the diagram above, tympanic membrane.
• With two separate passageways (and membranes), some birds are able to
generate two different sounds at the same time:
• hear a 'self-duet' by a Clay-colored Robin
(Source: Doug Von Gausig's webpage at
The sound of the song
• Characteristics of the sound (e.g., frequency) are influenced by vibrations of
the internal tympaniform membrane (ITM).
• Superfast syringeal muscles -- Elemans et al. (2004) have found that Ring
Doves (Streptopelia risoria) use "superfast" muscles to make their
distinctive call. The dove's familiar cooing sound includes a trill, which is
caused by an airflow that makes membranes in the syrinx vibrate.
• The quality of sound can be further influenced by tracheal length, by
constricting the larynx, by muscles in the throat, or by the structure and/or
movements of the bill (e.g., here are some complex 'Bird Songs in Slow
• Although the above model has been generally accepted, Goller and Larsen
(1997a, 1997b, 1999) provide evidence that other structures (not the ITM)
are the source of sound in both songbirds (oscines) and non-songbirds
because birds can still vocalize when the medium (or internal) tympaniform
membrane is experimentally kept from vibrating.
• Birdsong sounds sweeter because throats filter out messy overtones
songbirds adjust the size and shape of their vocal tract to 'fit' the changing
Control of the song
• Central motor control : Different circuits (or impulse pathways) in
the brain control song production (posterior descending pathway)
and song learning (anterior forebrain pathway).
• Song production is controlled via a pathway beginning in the brain
& travelling to the syrinx
• Testosterone (and melatonin) appear to play a role in song
– Autoradiographic studies have shown that the neurons of the songcontrolling nuclei incorporate radioactive testosterone, whereas other
regions of the brain do not (Arnold et al. 1976).
– Male Zebra Finches - correlation between the amount of song & the
concentration of serum testosterone (Pröve 1978)
– Seasonal changes in testosterone levels correlated with seasonal singing
When testosterone levels are low, decrease in song & a decrease in size of male-specific brain nuclei (Nottebohm 1981).
In adult Chaffinches, castration eliminates song, but injection of testosterone induces such birds to sing even in November,
when they are normally silent (Thorpe 1958).
– Females in some species can be induced to sing by injecting them with
testosterone (Nottebohm 1980).
Spectrograms of hoots from three different
male Scops owls showing the variation in
Male quality and owl hoots 1
• The evolution of communication through intrasexual selection is expected
to lead signalers to transmit honest information on their fighting ability.
• Hardouin et al. (2007) studied information encoded in acoustic structure of
territorial calls of a nocturnal raptor.
• During territorial contests, male Scops Owls (Otus scops) give hoots
composed of a downward frequency shift followed by a stable plateau.
• Hardouin et al. (2007) found that the frequency of the hoot was negatively
correlated with the body weight of the vocalizer.
• They shifted the frequency of natural hoots to create resynthesized calls
corresponding to individuals of varying body weight and used these stimuli
in playback experiments simulating an intrusion into the territory of
established breeders.
• Territory owners responded less intensely when they heard hoots
simulating heavier intruders, and males with heavier apparent weight
tended to give hoots with a lower frequency in response to playbacks
simulating heavier intruders.
Male quality and owl hoots 2
• Although the current lack of understanding of the mechanisms of voice
production in owls limits our ability to discuss the bases of this
relationship, one possibility is that it may result from physiological
constraints that operate during sound production.
• For example, lower-pitch hoots may be more costly to produce and/or
reflect superior muscular or respiratory abilities.
• The relationship between pitch and body weight may reflect the fact that
heavier, better-condition males are also characterized by higher
testosterone levels, which in turn affect the frequency of their
• Indeed, male condition and testosterone levels have been shown to
positively correlate, and higher testosterone levels are typically associated
with more intense sexual displays.
• Moreover, experimental studies have demonstrated that injections of
testosterone lower the frequency of male calls in birds, e.g., Gray
Partridges (Perdrix perdrix) and Zebra Finches (Taeniopygia guttata).
Melatonin Shapes Brain Structure In
• Springtime's lengthening days spark the
growth of gonads and a rush of sex hormones
that drive songbirds to melodic song.
• Bentley et al. (1999) also identified melatonin
as a critical ingredient that regulates singing
and fine-tunes the effects of testosterone on
the brain
Sexual differentiation of the avian brain
• In songbirds, males and females may
have distinctly different brain structures,
specifically in those areas involved in the
production of song.
• In many songbirds, males sing while
females do not (or sing very little).
• The ability to sing is controlled by six
different clusters of neurons (nuclei) in
the avian brain (see diagrams below).
Neurons connect each of these regions to
one another.
• In male songbirds, these nuclei can be
several times larger than the
corresponding cluster of neurons in
females, and in some species (e.g., Zebra
Finches), females may lack one of these
regions (area X) entirely (Arnold 1980,
Konishi and Akutagawa 1985).
Classification of Bird Sounds 1
1. Songs
– primarily under the influence of sex hormones
– generally important in reproduction (e.g., defending territories & attracting
2. Calls
– generally concerned with coordination of the behavior of a pair, family group,
or flock (e.g., several vocalizations of Carolina Chickadees)
– not primarily sexual, but important in 'maintenance' activities, such as foraging,
flocking, & responding to threats of predation
– usually are acoustically simple (e.g., contact notes of Northern Cardinals)
– may serve a variety of functions:
• location/contact/individual recognition [Montezuma Oropendola contact calls]
• Slaty-tailed Trogon calling
(Mayflower Bocawina National Park - Belize.. (more))
Classification of Bird Sounds 2
3. nocturnal flight calls. These calls help birds form and maintain inflight associations, and also provide locational information that helps
flying birds avoid collisions.
Nocturnal flight call of a Black-and-White
RealAudio | AIFF | WAV (at 1/6 speed:
RealAudio | AIFF | WAV)
Video of Black-and-white Warbler at
Mayflower Bocawina National Park, Belize
Classification of Bird Sounds 3
4. distress (Listen to a Downy
Woodpecker distress call)
Sonograms of distress calls
from six species.
(a) Sootycapped Bush-Tanager,
(b) Black-capped
(c) Green Violet-ear
(pictured below),
(d) Gray-breasted WoodWren,
(e) Streak-breasted
Treehunter, and
(f) Yellowish Flycatcher.
Each sonogram
represents 1 sec of
distress calling.
Distress Calls of Birds in a Neotropical
Cloud Forest 1
• Neudorf and Sealy 2002 -- Distress calls are loud, harsh
calls given by some species of birds when they are
captured by a predator or handled by humans.
• recorded the frequency of distress calls in 40 species of
birds captured in mist nets during the dry season in a
Costa Rica cloud forest.
• They tested the following hypotheses proposed to
explain the function of distress calls:
(1) calling for help from kin or reciprocal altruists;
(2) warning kin;
(3) eliciting mobbing behavior;
(4) startling the predator;
(5) distracting the predator through attraction of additional predators.
Distress Calls of Birds in a Neotropical
Cloud Forest 2
• results did not support calling-for-help, warning kin, or mobbing
• genera that regularly occurred with kin or in flocks were not more likely to
call than non-flocking genera.
• no relationship between calling frequency and struggling behavior as
predicted by the predator startle hypothesis.
• Larger birds tended to call more than smaller birds, providing some support
for both the predator distraction and predator startle hypotheses.
• Calls of higher amplitude may be more effective in startling the predator.
• Distress calls of larger birds may also travel greater distances than those of
smaller birds, supporting the predator manipulation / distraction
• The adaptive significance of distress calls remains unclear as past studies
have generated conflicting results.
• While more playback experiments are necessary to determine if calls
indeed attract other individuals or predators, these results suggest that
distress calls do not function to attract helpers or mobbers but are more
likely directed toward predators.
Classification of Bird Sounds 4
copulation or post-copulatory (e.g., see 'Calls' section of this
account of Broad-winged Hawks and this description of
copulation in Burrowing Owls)
9. begging (e.g., young Downy Woodpeckers while being fed)
Kookaburra nest
10.alarm (aerial predator vs. ground predator) [for an example
of crow alarm calls check; also listen to the alarm
call of a Masked Antpitta, Hylopezus auricularis]
Alarm calls
• Domestic Chicken - aerial predator alarm call
• Domestic Chicken - ground predator alarm call
Alarm calls
• White-breasted wood wren
Chickadee language 1
• Black-capped Chickadees (Poecile atricapilla) have a complex language for
warning flock-mates about predators.
• It was already known that chickadees utter a high-pitched "seet" when a
predator was overhead, and used their "chick-a-dee" call to, among other
things, alert flock-mates to mob a threatening bird that was perched.
• However, Templeton et al. (2005) put flocks of six chickadees in an
enclosure and recorded their responses.
• In the presence of a harmless quail, chickadees gave no alarm.
• But when a tethered raptor (hawk or owl) entered the cage, the alarms
• Alarms were more frequent when Saw-whet and Pygmy owls were present.
• But the alarms also had a different sound.
• In the presence of small predators, the chickadees tacked an average of four
"dees" to their call: "chick-a-dee-dee-dee-dee."
• When the larger, but less dangerous, Great Horned Owl was present, they
used two dees: "chick-a-dee-dee."
• Smaller predators are more dangerous because of their greater agility
Chickadee language 2
• To prove that the "language" was conveying information,
Templeton et al. (2005) played back the recordings to
• Recordings made in response to more dangerous raptors
elicited more mobbing behavior, confirming that the
chickadees understood the meaning of the calls.
• While this may be the most sophisticated bird "vocabulary"
found to date, Templeton suspects others are out there.
• This is the most detailed communication we have found,
but it is also the finest scale that anyone has looked.
• All these signaling systems are a lot more complicated than
we really expect, until we spend a lot of time and energy
looking at them
Predator wingspan compared to the number of "dee" tones on the end of the
chickadees calls. The smaller (and more agile) the predator, the more "dees" get
added, suggesting that chickadees recognize the danger of smaller predators.
Hear a chickadee response to a
Pygmy Owl - click here.
Hear a chickadee response to a Great
Horned Owl - click here.
Black-capped chickadee video
Nuthatches eavesdrop on chickadees
• Many animals recognize the alarm calls produced by other species,
but the amount of information they glean from these eavesdropped
signals is unknown.
• Black-capped Chickadees (Poecile atricapillus) have a sophisticated
alarm call system in which they encode complex information about
the size and risk of potential predators in variations of a single type
of mobbing alarm call.
• Templeton and Greene (2007) showed experimentally that Redbreasted Nuthatches (Sitta canadensis) respond appropriately to
variation in heterospecific "chick-a-dee" alarm calls (i.e., stronger
mobbing behavior to playback of small-predator alarm calls),
indicating that they gain important information about potential
predators in their environment.
• These results demonstrate a previously unsuspected level of
discrimination in intertaxon eavesdropping.
• Siberian Jay (Photo by John van der
Calls 'describe' predator's behavior
• Predation may cause natural selection, driving evolution of antipredator calls.
• calls can communicate predator category and/or predator distance
• risk posed by predators depends also on predator behavior, and ability of prey to
communicate predator behavior to conspecifics would be a selective advantage
reducing predation risk.
• Griesser (2008) tested with Siberian Jays (Perisoreus infaustus), a group-living bird
• Predation by hawks, and owls, is substantial and sole cause of mortality in adults
• Field data and predator-exposure experiments revealed jays use antipredator calls
depending on predator behavior.
• playback experiment demonstrated that prey-to-prey calls are specific to hawk
behavior (perch, search, or attack) and elicit distinct, situation-specific responses.
• first study to demonstrate that prey signals convey information about predator
behavior to conspecifics.
• Given that antipredator calls by jays serve to protect kin group members, lowering
mortality, kin-selected benefits could be an important factor for the evolution of
predator-behavior-specific antipredator calls in such systems.
Photo by D. DeMello, Wildlife Conservation Society
Low frequency calls of
cassowaries 1
• some birds can detect wavelengths in the infrasound range, there has been
litle evidence that birds produce very low frequencies.
• Mack and Jones (2003) made 9 recordings of a captive Dwarf Cassowary
(Casuarius benneti) and one recording of a wild Southern Cassowary (C.
casuarius) in Papua New Guinea.
• Both species produced sounds near the floor of the human hearing range in
their pulsed booming notes: down to 32 Hz for C. casuarius and 23 Hz in C.
Low frequency calls of cassowaries 2
• Natural selection should favor evolution of vocalizations that reach targets
with minimal degradation, and low frequencies propagate over long
distances with minimal attenuation by vegetation.
• New Guinea forests often have a fairly thick understory of wet leafy
vegetation that could quickly attenuate higher frequencies.
• very low frequency calls of cassowaries probably ideal for communication
among widely dispersed, solitary cassowaries in dense rainforest.
• How cassowaries produce such low vocalizations is currently unknown.
• All three cassowary species have keratinous casques rising from the upper
mandible over the top of the skull up to 17 cm in height.
• Hypotheses concerning the function of the casque include:
(1) a secondary sexual character,
(2) a weapon in dominance disputes,
(3) a tool for scraping the leaf-litter, or
(4) a crash helmet for birds as they bash through the undergrowth.
• The later three seem unlikely based on field observations.
• Future research should include the possibility that casque might play some
role in sound reception or acoustic communication.
Energetic cost of singing
• Sexually selected displays, such as male passerine bird song, predicted to be
• measurements calculating rate of oxygen consumption during singing using
respirometry have shown that bird song has a low energetic cost.
• Because birds are reluctant to sing when enclosed in a respirometry
chamber, energetic cost of singing could differ under more normal
• Ward and Slater (2005) used heat transfer modeling, based on thermal
images, to estimate the energetic cost of singing by Canaries (Serinus
canaria) not enclosed in respirometry chambers.
• Metabolic rate calculated from heat transfer modeling was 14% greater
than during standing, suggesting song production is metabolically cheap for
passerines and the metabolic cost small enough that it is unlikely to
represent important fitness cost
• However, cost will increase as the temperature decreases.
The functions of bird song 1
• may vary among species; some known & hypothesized
functions include:
1. Identification
– Songs have characteristics that permit other birds to identify the species, sex (if
both males and females sing), and individual identity of a singer.
– Characteristics important in permitting specific, sexual, & individual recognition
vary among species but may include (Becker 1982):
• song duration
• interval between song elements (also called notes or syllables, e.g., see
sonagrams of Mangrove Warbler songs)
• frequency
• syntax - the order of elements within a song (e.g., Tropical Mockingbird)
• structure of elements, e.g., duration and frequency
2. Mate attraction
3. Territory establishment and defense
Motivation and Fitness - Birds may provide information to conspecifics by
variation in (Becker 1982):
– singing rates
may increase during aggressive encounters
may be higher in higher quality males
– song duration - may increase or decrease (depending on the species) during
– song amplitude (or volume) may decrease during aggressive encounters
– song frequency - may increase during conflict situations (e.g., Indigo Buntings;
Thompson 1972)
– song complexity - songs may consist of more or fewer elements during conflict
situations (e.g., male Blue Grosbeak utter songs with more syllables during
aggressive encounters with other males)
Distraction of potential predators (e.g., Common Yellowthroat flight song)
Coordination of activities
Stimulate females
Attract females for extra-pair copulations
Mate guarding
Song complexity and the avian immune system 1
• There are three hypotheses to explain how evolution of parasite
virulence could be linked to evolution of secondary sexual traits, such
as bird song.
1. female preference for healthy males in heavily parasitized species
may result in extravagant trait expression.
2. a reverse causal mechanism may act, if sexual selection affects
coevolutionary dynamics of host-parasite interactions by selecting
for increased virulence.
3. immuno- suppressive effects of ornamentation by testosterone or
limited resources may lead to increased susceptibility to parasites in
species with elaborate songs.
• Assuming a coevolutionary relationship between parasite virulence
and host investment in immune defense, Garamszegi et al. (2003)
used measures of immune function and song complexity to test
passerine birds.
Song complexity and the avian immune system 2
• Under the first two hypotheses, they predicted avian song
complexity to be positively related to immune defense among
species, whereas this relationship was expected to be
negative if immuno-suppression was at work.
• They found that adult T-cell mediated immune response and
the relative size of the bursa of Fabricius were both positively
correlated with song complexity, even when potentially
confounding variables were held constant.
• These results are consistent with the hypotheses that predict
a positive relationship between song complexity and immune
function, thus indicating a role for parasites in sexual
• Regression of short-term song complexity (number of unique syllables within
songs/song length) on T-cell mediated immune response, after removing
allometric effects by using residuals after controlling for body mass. Datapoints are
phylogenetically independent linear contrasts (N = 38). The line and equation are
from linear regression forced through the origin.
Cities change the songs of birds
• rise of urban noise levels are a threat to living conditions in and around
• Urban environments typically homogenize animal communities, results in
same few bird species everywhere.
• Insight into the behavioral strategies of urban survivors may explain
sensitivity of other species to urban selection pressures.
• Slabbekoorn and den Boer-Visser (2006) showed songs that are important
to mate attraction and territory defense have significantly diverged in Great
Tits (Parus major), a successful urban species.
• Urban songs shorter and sung faster than in forests, and often atypical song
• consistently higher minimum frequencies in ten out of ten city-forest
comparisons from London to Prague and from Amsterdam to Paris.
• Anthropogenic noise is likely a dominant factor driving these changes.
• These data provide evidence supporting acoustic-adaptation hypothesis
• reveal a behavioral plasticity that may be key to urban success; and lack of
which may explain detrimental effects on bird communities that live in
noisy urbanized areas or along highways.
In some species, females also sing.
• This is particularly true in the tropics (see 'duetting'). Singing
by females may be important in:
1. territory defense (particularly in keeping other females out of
a territory)
2. mate guarding
3. pair-bonding / attraction
4. reproductive synchronization
When do female birds sing?
Hypotheses from experimental studies
(Langmore 1998).
(a) The song of a female Superb Fairy-wren. Females use songs to defend territories
against both males and females.
(b) The song of a female Alpine Accentor. Female Alpine Accentors sing to attract
males, and complexity increases with age. This song was a two-year-old female
(Langmore 1998).
Singing by female Northern Cardinals
• Yamaguchi (2001) found female Northern
Cardinals learn to sing three times faster than
males - the most dramatic example of learning
disparities between male & female animals found
to date.
• She collected nestling cardinals & raised them in
sound chambers with microphones and speakers
that play back the songs of adult cardinals.
• It takes about a year for a cardinal to learn to sing,
and young songbirds learn by imitating adults.
• During the early sensitive phase, young don’t sing,
but listen to singing adults to memorize their
• Then the practicing begins.
• initial attempts are pretty miserable
• they practice until it matches the memory that
was formed earlier during the sensitive phase
Singing by female Northern Cardinals 2
Yamaguchi (1998) also analyzed songs and found females sing with
more overtones, a slightly nasal sound.
Young males also go through a nasal, warbly phase as their
testosterone levels rise, but it’s as though females continue to sing
with an adolescent male’s voice.
Yamaguchi (2001) discovered female cardinals memorize adult songs
three times faster than males.
While both sexes ultimately learned same number of song types,
females’ sensitive phase was only a third as long as the males’.
The different learning rates may reflect an evolutionary adaptation.
Like other songbirds, juvenile cardinals disperse from their parents’
territory about 45 days after hatching to establish their own turf
before their first breeding season.
Singing by female Northern Cardinals 3
• Away from their nest, young cardinals are suddenly immersed in new song dialects
of other adult cardinals.
• It appears that females lose the ability to learn new dialects when they disperse,
while males are able to learn them and “fit in” with their new neighbors.
• Perhaps males retain the ability to learn songs longer than females so that they
can have a better chance of establishing territory in a new area
• For males, song-matching and fitting into the crowd in a new place are really
important, while they’re not for females
• It’s not clear why female cardinals have a shorter window of vocal learning, but we
don’t really know why females sing at all, or how they use their songs
• One hypothesis is that females sing as a species identification tool, a greeting to
male cardinals that says, “I’m an eligible mate; come court me.”
• Others have proposed female cardinals sing to shoo away brightly colored mates
from the nest, warning the males not to attract attention to the vulnerable chicks.
• female cardinals also use songs in aggressive behavior
• Yamaguchi says “I’ve seen females battling each other in the field, and they’re
singing the whole time as they bang into each other.”
Male northern cardinal
Tucson, Arizona