Reel-to-reel tape recorder

How birds hear songs

Sound recording has played a vital role in research into the vocal communication of birds. One question it's answered about birdsong is "do birds hear birdsong as we do?" 

Do birds hear birdsong as we do?

The first step towards answering this question was provided by sound recordings of a whip-poor-will, a North American species of nightjar. The bird's name is a verbalisation of its song. It says “whip-poor-will” - a three note phrase. When, however, 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) 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.

The wren's song phrase

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 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.

Multiple phrases

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, a male sang “see me - hear me” 22,197 times. Such a bird must reiterate its song a million times a season.

Seeing with sound

There are a few species of bird, breeding in the total darkness of large caves, that use sounds not for communication but to “see in the dark”. Like many bats, these creatures echolocate. As is well-known in bats, a short sharp sound is created by the bird, the echo is then listened to, the time gap assessed and an appropriate response made, e.g. turning left if you are about to collide with a stalagtite.

One such feathered echolocator is the oilbird of north-eastern South America, a large nightjar-like bird that feeds at night on fruit. The others are certain species of swiftlet from the Oriental and Australasian zoogeographical regions. They are the birds whose nests are used for soup, the best-known species and colony being the black-nest swiftlet of the Great Niah caves in Sarawak (Borneo).

  • Jeffery Boswall
  • Jeffery Boswall (1931-2012) was a natural history broadcaster, film-maker and producer. He is best known for his radio and television work with the BBC Natural History Unit. His notable titles include Animal Magic, The Private Life of the Kingfisher, and Wildlife Safari to Ethiopia. Jeffery co-founded the National Sound Archive's wildlife section with Patrick Sellar in 1969.