The language of birds: 1.4 How does one bird hear another's song?
It was with the aid of a tape recorder that the ornithologist who
studied the marsh warbler was able to compare the copyist's copy
with the originator's original. The tape recorder has played a vital
role in research into the vocal communication of birds. One question
about bird song to which the answer was long suspected, but which
was finally answered with tape recordings is "do birds hear
bird songs as we do?". The species recording that provided
the first step towards the answer was of a whip-poor-will Caprimulgus
vociferus, a North American species of night jar. The bird's
name is a verbalisation of its song. It says "whip-poor-will"
- a three note phrase. When, however, using the tape replay machine
as a kind of sound microscope you slow down the recording, it is
clear that the bird sings five notes, but their temporal arrangement
is such that, when heard in the wild (or at natural speed off a
tape) the five notes sound like three. There is no means of knowing
whether other whip-poor-wills hear three or five, though it is not
unreasonable to suggest that if they were deaf to the subtlety,
the subtlety would probably not exist.
The second, highly ingenious stage in the answer, was to slow
down a recording of a mockingbird copying a whip-poor-will. Lo and
behold, the mocker produces a five note imitation! It can thus be
assumed that other whip-poor-wills also hear five-note songs. It
is to be expected that the smaller the bird, the better able it
will be at separating out a succession of fast-arriving sounds.
For a bird like the wren a factor of ten is suggested. Thus by slowing
down a tape recording of a wren's song phrase three times, one to
two, two to four, and four to eight times as long (and three octaves
down as well) we approach the degree of separation that one wren
experiences in another wren's song - furthermore it is a musical
revelation! One song phrase 8.25 seconds long, when stretched out
to 66 seconds, reveals 103 notes, which means that the bird is singing
at a rate of 740 notes to the minute! Slowed down this way, a wren's
song phrase is at once more intelligible. If you follow it by the
same recording at normal speed, the impression is of a hurried song.
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Wren Troglodyes troglodytes in song. The song of
the Wren represents a pinnacle of avian song complexity.
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To sum up: when a typical songbird, say a chaffinch, is singing,
he is saying "I am a chaffinch", "I am a cock chaffinch",
"I am a particular cock chaffinch","I am here",
"I am in my territory", "I am ready to posture at
and drive off other cock chaffinches" and if unmated "I
am ready to take a mate". Each time a cock chaffinch sings
"chip, chip, chip; cherry-erry-erry; fissychooee-o!"
it takes him about 2.5 seconds, in 12 hours he says that phrase
3,300 times.
The world record for songs per day is held by the North American
red-eyed vireo Vireo olivaceus, a male sang "see me
- hear me" 22,197 times! Such a bird must reiterate its song
a million times a season.
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