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

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

Each songbird species has its own set of vocalizations whose 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.
  • 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.
  • 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
  • May be used outside the nesting season.

Every song and call has its own 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 don't use their mouth or tongue to change how a vocalization

What songs and calls do Tree Swallows make?
Tree Swallows make many different vocalizations throughout the year.  Here are five
calls and one song you're sure to hear during the nesting season.

Chatter Call:  (click name for YouTube video).
  • A loud, rapid, repeating monotone she-she-she-sheet.  
  • You're certain to hear chattering early in the nesting season as boxes are
    claimed and pairs formed.  Both males and females chatter 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 approaching swallows (see
    picture above).  
  • This combination of postures and sound form a classic territorial display.  
  • When males chatter at other males it appears to mean "this nest site is mine;
    keep away."  
  • When males chatter to females it can mean "this nest site is mine; come see."
  • Females may also chatter to repel intruding females.

Shriek or Alarm Call:  (click name for YouTube video).
  • A very loud and high-pitched, single or double-noted, peeh or pee-peeh.
  • Tree Swallows may add shrieks with chatters when other swallows intrude too
    close to their nest sites.  
  • Shrieks also function as alarm calls when potential predators, especially avian
    predators, are spotted.  Shrieks lets predators know they've been seen and
    stimulates other swallows in the area to join in sounding the alarm or to flee.
  • Be prepared to be shrieked at when you make box checks.

Gurgle or Contact Call:  (click name for YouTube video).
  • A rather soft and low-pitched 2 to 4 note repetition of buli-duli-dullit.  
  • Although gurgles are heard throughout the nesting season, they're especially
    noticeable during pairing as males and females become accustomed to each
    other as they bond.
  • Gurgles vary slightly from swallow to swallow, which probably helps pair
    members recognize each other's identity and location.
  • Gurgles are also given during incubation of eggs and brooding of small young
    when pair members relieve each other at the nest.  
  • Adults sometimes gurgle when they arrive at the nest with food for their young,
    which may help stimulate the nestlings to beg.

Anxiety Call:  (click name for YouTube video).
  • A rather sweet, pure, repeated eur or euree.
  • Anxiety calls are sometimes given by territorial individuals or pairs when other
    swallows approach or intrude near their nest site.

Ticking Call:  (click name for YouTube video).
  • A rapid tic-tic-tic-tic.
  • Ticking is associated with mating, and is given when males swoop down to
    perched females just prior to and during copulation.  
  • Females sometimes give it to perched males, and in this circumstance it seems
    to signal her willingness to copulate.  
  • Tree Swallows also may give a harsh version of the tick when they dive on nest
    competitors or potential predators, as you'll see when you make nest checks.

Song:  (click name for YouTube video).
  • There is one main Tree Swallow song, given mostly but not exclusively by
    breeding males.
  • In contrast to most calls, which are rather monotone, the Tree Swallow song
    usually includes notes that sweep up and down, plus various chirps and gurgles,
    all strung together in 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 when eggs are being laid and
  • Tree Swallows usually sing while perched near or at the nest site, 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
some of their quirks.

Questions for the next Topic:  Nest Site Competition and Box 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?

Tree Swallow Song and Calls
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