Song and Calls

At the Project:
The number of swallows inspecting your nest boxes is growing as more arrive, and
one thing is certain, for small birds Tree Swallows can make a racket!

You'll be hearing lots of Tree Swallow vocalizations in the weeks to come.  Now is a
good time to start listening carefully, seeing if you can distinguish specific calls and
song, and noting what situations and behaviors seem to evoke and accompany them.















Concepts:
Each songbird species has its own set of vocalizations.  Numbers can range from a
few up to hundreds or even thousands of different calls and songs in some species.  
Each vocalization is a signal, with a specific purpose, given in specific circumstances.  
Vocalizations and visual displays are the main tools birds use to communicate with
and exert influence over other birds.

Calls and songs have many functions, among them:
  • Species recognition.
  • Sexual recognition.
  • Individual recognition.
  • Assessing individual quality.
  • Impressing potential mates.
  • Establishing and maintaining pair bonds.
  • Establishing and maintaining territory.
  • Establishing and maintaining dominance hierarchies.
  • Attaining extra-pair copulations.
  • Maintaining contact with others.
  • Sounding predator alarms.
  • Mobbing and aggression toward predators.

Ornithologists often distinguish between songs and calls.
Songs:
  • Are usually louder, longer, and more complex than calls.
  • Are often given from a conspicuous position.
  • Are most often produced by males.
  • Proclaim a bird's species and its individual identity.
  • Function to repel intruders and defend territory.
  • Also function to attract and stimulate females.
  • Are mostly involved with nesting season activities.
  • May not be completely instinctive.  In some species young birds must learn
    their species' songs by listening.
Calls:
  • Are shorter and simpler than songs.
  • Convey specific messages about immediate, often urgent situations, such as
    danger, hunger, one's location.
  • Alert others of one's current feelings or intentions.
  • May be given by both males and females.
  • Are instinctive and understood by all birds of a species.  They do not have to
    be learned.
  • May be used outside the nesting season.

Every song and call has qualities, including:
  • Sound wave frequency.
  • Loudness.
  • Duration.
  • Time between vocalizations.

The possibilities for variation are many, both among species and among individuals of
each species.  Some vocalizations seem rather simple, others extremely complex to
our ears.  But birds almost certainly hear and interpret sounds quite differently from
us, and we really don't know what aspects of songs and calls birds key on.

How do songbirds make songs and calls?
  • Unlike us, birds don't have vocal chords in their throats for sound production.  
    Instead they use a completely different sound producing organ, the Syrinx,
    that only birds possess.
  • The syrinx is a box-like chamber of cartilage, with supporting muscles, and
    membranes that can stretch and vibrate.
  • The syrinx (below in pink) is not located in the throat but deep in a bird's chest
    where its trachea (windpipe) branches into two tubes leading to the its lungs.














  • Sounds are produced when air being expelled rapidly from a bird's lungs passes
    through the syrinx.  As the air flows past, muscles change the syrinx's shape,
    causing sound waves to be generated by the syrinx's vibrating membranes.
  • The syrinx-controlling muscles can influence the tone, pitch, volume, and
    rhythm of the sound.
  • Unlike us, birds do not use their mouth or tongue to change the character of a
    vocalization.











What songs and calls do Tree Swallows make?
Tree Swallows vocalize throughout the year, but since you'll be observing them during
nesting, here are four important calls and one song you're sure to hear and should be
able to distinguish.

Note:  Three of the four calls and the song described below are linked to Cornell
University's Macaulay Library of Natural Sounds.  This is a tremendous resource which
you will probably want to explore at length.  However, you will need the free Adobe
Flash Player in order to play sounds from their catalog.

Chatter Call:  A loud, rapid, repeating monotone she-she-she-she-sheet.  This is the
most common call you'll hear early in the nesting season as boxes are being claimed
and pairs formed.  Both males and females give it when other swallows approach their
nest site.  Chattering swallows usually appear excited or agitated, flattening their
bodies, fluttering their wings, and aiming their heads at the other swallow while the
call is made (see picture above).  This combination of postures form a classic
territorial defense threat display.  When given by males to other males it seems to
mean "this nest site is mine, keep away".  When males give it to females it can be
mean "this site is mine, come and see".  Females also give the Chatter Call to repel
intruding females.

Gurgle, or Contact Call:  A rather soft and low-pitched 2 to 4 note repetition of buli-
duli-dullit.  The Gurgle varies slightly from swallow to swallow and probably helps pair
members recognize and bond with each other.  Although it is heard throughout the
nesting season, it's especially noticeable during pairing as males and females become
used to each other's presence at the cavity, and then again later during incubation
and brooding of small young when pair members relieve each other at the nest.  It
may act to alert the other of the first's presence and location.  Adults also Gurgle
when they arrive at the nest with food for their young, which may help stimulate
nestlings to beg.

Alarm Call:  A high-pitched, loud, single or double-noted,  pee-peeh, often given
with the Chatter Call when other swallows intrude close to nest sites.  It is also given
when potential predators, especially avian predators, are spotted.   It lets the
predator know it's been seen and stimulates other swallows in the area to join in
sounding the alarm or to flee the area.  

Ticking Call:  This rapid tic-tic-tic-tic is associated with mating, and is given when
males swoop down to perched females just prior to copulation.  Females sometimes
give it to perched males, and in this circumstance it seems to signal her willingness to
copulate.  Tree Swallows give a harsher version of the Ticking Call when they dive on
potential predators, as you'll see when you make nest checks.

Song:  There is one main Tree Swallow song, given mostly but not exclusively by
breeding males.  In contrast to calls, which are rather monotone, the Song includes
notes that sweep up and then down, plus various chirps and gurgles, all strung
together in countless different combinations that vary from bird to bird.  Song is
most commonly heard after pairs are well-established at nest sites.  Listen for it
when nests are being built, and eggs are being laid and incubated.  Swallows usually
sing while perched at the box, although they sometimes sing in flight.  As with most
songbirds, Tree Swallow Song seems intended to repel intruders of their own species,
to intimidate potential opponents who venture too close to their "center of
reproductive interest", in this case the male's nest cavity.

As the nesting season at your project advances listen for other, less frequently given
vocalizations, and note the situations in which they occur.
Also, listen for individual differences among your swallows; it seems there's always
one that screams Alarms at every other swallow that passes, or one that always Ticks
and dives on you when you check its nest, or one that Chatters at an odd pitch or a
slower rate.  Part of the fun is realizing these birds really are individuals and getting
to know their personal quirks.










Questions for the next Topic:  Nest Site Claiming.
  • Why don't Tree Swallows spend the winter at your project?
  • Where do they go during winter months?
  • Why are they back here so early in spring?









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