Matt Johnson
Lecture Notes
ORNITHOLOGY
(Humboldt State Univ. WILDLIFE 365)
LECTURE 16 – VOCAL COMMUNICATION
I.
Introduction.
 Last lecture we talked about visual communication. While it is true birds are wellknown for spectacular plumage and visual displays,
 Bird vocalizations are nothing short of phenomenal. Indeed, birds have the greatest
sound producing capabilities of all vertebrates.
II.
The physics of bird voice.
A. Bird vocalizations are arbitrarily categorized into songs and calls.
1. Songs are typically long vocalizations with specific repeated patterns.
They are most often performed, but not always, by males during the
breeding season. Ex: Indigo Bunting (TAPE AND SLIDE).
2. Calls are typically short simple vocalizations, usually given by both sexes.
There are many varieties of calls including contact calls, distress calls,
flight calls, etc. TAPE
3. But this distinction is arbitrary; there is no clear distinction between songs
and calls in their structure or function – when considering all birds, there
is a gradient from call to song. Nonetheless, within a single species, it is
often easy to distinguish between short non-breeding calls, and longer
breeding songs.
B. Physical attributes of vocalizations.
1. One major, and real, distinction in vocalizations exists in the acoustical
structure of bird sounds:
a. Whistled songs. These are pure or nearly pure sound waves. The
higher the pitch, the higher the frequency of wave oscillation
(measured in Hz, or cycles per second). They may or may not sound
like true whistles. Ex: Blackpoll Warbler, Sage Grouse TAPE.
Whistled songs lack what are called “harmonics,” which are multiple
sound waves of different frequencies stacked on top of one another.
b. That brings us to the second type of song -- Harmonic songs.
Harmonic songs are comprised of several frequencies that are
multiples of each other, which in musical terminology means they are
in different octaves. Usually, one frequency is louder (higher
amplitude) than the others – it is the dominant tone, the other
frequencies are overtones. In the Red-winged Blackbird, the overtones
give the call a nasally quality. TAPE In the Catharus thrushes, like
the Swainson’s thrush, overtones are at odd multiples, giving the song
an ethereal, flute-like quality. TAPE
2. What these differences mean to a listener.
III.
IV.
a. The physical structure of a call affects the ease with which a listener,
such as predator or a potential mate, can locate its source.
b. Short notes with broad frequency ranges are easy to locate – good for
contact calls.
c. Long, high, thin calls are more difficult to locate – good for alarm
calls. (long difficult to locate due to bouncing)
d. Low frequency songs are best for long distance communication, and in
high interference habitats such as forests – good for species like Great
Horned Owls. TAPE
e. In contrast, higher, buzz-like calls are effective for open habitats, such
as grasslands (Ex: Grasshopper Sparrow TAPE). In fact, closely
related birds in forest and field have very different song structures.
The syrinx.
A. All songs and calls come from the syrinx, formed at the junction of the two
bronchi and the trachea.
B. Air from the main anterior air sacs is forced thru the syrinx, where it vibrates
tympaniform membranes. OVERHEAD
C. The efficiency of sound production is extraordinary nearly 100% of air
vibrates to make sound; only about 2% is so used in humans.
D. Syringeal muscles control the details of the syrinx action during song
production, changing the pressure provided by the interclavicular air sac, the
tension of the membranes, and shape of entire structure. Birds also produce
syllables by rapid contraction of the chest muscles.
E. Range is truly phenomenal. The Brown-headed cowbird has largest range of
any single bird. 700 to 11,000 Hz. TAPE
F. Some birds, it has recently been learned, produce two independent sounds thru
the syrinx – OVERHEAD and TAPE (save tape until end) Woodthrush.
Avian vocabularies.
A. Just like birds have repertoires of visual displays, so too do they have a
repertoire of songs and calls used for various functions.
B. Steller’s Jays – Contact Calls, Alarm Calls, etc. TAPE
C. Many birds have rare calls used for very specific purposes: precopulatory
calls, juvenile begging calls, etc.
D. The typical “songs” of most songbirds have two primary functions: to (1)
signal potential rivals that a site is occupied and/or defended, and (2) advertise
to unmated females.
1. When territorial males are removed from their territories, they are usually
replaced very quickly by other males “floating” in the background waiting
for an opportunity. But when the removed male is replaced by a speaker
broadcasting the species’ song, replacement takes significantly longer.
2. Once a male forms a pair bond with a female, he sings less. Take her
away and he resumes singing.
3. Many birds vary their song for these two functions. Many warblers have
what are called accented ending songs to ward off rival males
TAPE….and serial song to attract a mate. TAPE All of this sounds so
honest, so faithful. Oh, I’m sorry, I’m already mated, so I’ll sing a song
V.
VI.
that says I am (just like a ring). Ah, but recent studies are documenting
that in forest songbirds long thought to be mainly monogamous, both male
and females are occasionally sneaking off for what are called EPCs: extrapair copulations. Males will often sneak away form their territory, then
start singing serial songs!
Recognizing species and individuals. Another primary function of bird song is
for identification of species or individuals.
A. Species ID.
1. Pairs of species that look very similar often have different songs: Alder vs.
Willow Flycatchers TAPE.
2. Species that inhabit dense foliage may distinguish each other call’s by
variation in phrasing. Gray Catbird vs. Brown Thrasher. TAPE.
B. Individual recognition.
1. Subtle differences in pitch, syntax, and timing enable birds to distinguish
individuals within a species.
2. This is well developed in the recognition of colonial nesting seabirds,
which need to pick their calling offspring out of a “sea” of others.
3. Also well developed in secretive but highly territorial species, such as
March Wrens and other songbirds inhabiting especially dense habitats.
a. A series of territorial males quickly learn to recognize each others’
songs, so that they avoid wasting energy defending a territorial
boundary with an individual with whom the boundary has already been
established.
b. Experiments have shown than Marsh Wrens respond much less
strongly to taped playbacks of their neighbors than to “fresh meat.”
But if their “neighbor” sings form the wrong side of their territory,
they very strongly react.
4. Some birds sing distinctive duets to recognize and strengthen pair bonds.
These are best developed in long-lived monogamous species, including
many tropical birds. TAPE of chachalaca or King Rail.
Song repertoires. Many species have large song repertoires – the question then is
why?
A. Function of large repertoires. Winter Wrens have varied song repertoires,
each song lasting up to 8 seconds and comprised 50 notes delivered in various
patterns form a pool of over 100 possible notes. TAPE So, why? 3
hypotheses:
1. Sexual selection: A large repertoire may indicate age and experience,
which females may preferentially select. Indeed, studies have shown that
female Canaries respond to large repertoires by building faster nests and
laying more eggs. And in Great Tits, males with the largest repertoires
produced the heaviest young.
2. A large repertoire may also thwart a neighbor's ability to track a bird’s
movement, which could confer advantages for feeding or for obtaining
EPCs.
3. Lastly, most birds’ response intensity to songs declines as that song is
repeated. Thus, a large repertoire may help prevent declining interest –
VII.
which could maximize the efficacy of a variety of song functions. Indeed,
the bird species that tend to sing the most continuously are the ones with
the largest repertoires. Ex, Mockingbird.
B. Vocal mimicry.
1. This brings us to vocal mimicry. The Mockingbirds is most famous for it
here, but there are many other species that mimic. In fact 15-20% of birds
in most regions practice vocal mimicry.
2. Some Mockingbirds know up to 150 songs, often performed surprisingly
like their original composers. TAPE?
3. In fact, some Mockingbirds sing songs from distant bird species – whether
these result from vagrants, or from the gradual passing of songs among
Mockingbirds past the original composer’s range is unclear.
4. Migratory mimics can have international repertoires. Marsh Warblers in
Europe sing African songs.
5. The leading hypothesis for vocal mimicry is that it is simply a function to
easily increase vocal repertoire, the evolutionary significance of which we
just went over. This idea is supported by the fact that Mockingbirds
clearly sing toward their mates or potential mates, and NOT toward the
species they are mimicking.
Song Learning.
A. The age old question – nature or nurture. The age-old answer: both.
B. Brood parasites have totally innate songs – they are raised not by their own
species so this makes perfect sense.
C. Other birds appear to develop vocalizations primarily via learning, especially
parrots.
D. But most birds have a combination, with perhaps a heavy influence of
inheritance.
1. The first time baby song sparrows hear their species’ song, their heart rate
increases. They have a “template;” sounds that do not match it illicit no
response.
2. Yet they cannot deliver “true” songs raised in captivity, they must hear it
to form a model from which to develop their song.
3. Studies on White-crowned Sparrows have revealed that young birds pass
thru 4 periods of song development.
a. Critical learning period. – When they first hear their song and store it
in memory. Lasts usually much less than a year.
b. Silent period. Usually winter. No practice, no hearing.
c. Subsong period. Analogous to infants’ babbling. Exploratory
syllables, quiet songs for practice, not communication. Late winter
early spring.
d. Song crystallization. – finalization of the song in environment of
conspecific singing. Usually a bird’s first spring and summer.
E. Heavy learned components to songs create regional variation in song forms –
dialects, just like human accents. White-crowned Sparrows living in Coastal
California have been well studied in this regard. Areas as small as a few
square kilometers can have their own dialects, and they can be persistent. The
Berkeley dialect has persisted for decades.

Lastly, we talk a lot about how bird songs are structured, how they evolved, and how
they influence birds. But that’s not all they influence. They influence the human
spirit as well. Perhaps not intentionally, but undoubtedly profoundly. I’ll close with
a quote from Henry David Thoreau: SLIDE