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The language of birds: 6.1 Instrumental sound production

The sound created by a woodpecker as it stabs its bill into a tree bark was no doubt entirely adventitious at one stage in the bird's evolution, as indeed it still is when the bird is feeding or chiselling out a nest or roost hole. But from this behaviour has evolved what might be called the woodpecker's jungle telegraph, a kind of avian tom-tom system. It might be supposed that the beating of such a tattoo allowed little room for subtlety, but recent research has revealed that not only can each drum-roll be assigned readily to species (as you might expect) but each can also - by a listening bird or birdwatcher - be identified as to sex and individual. The sonograms below display the different temporal patterns of the drumming "songs" of six different species of North American Woodpecker:

Sonogram - Yellow-bellied Sapsucker (3K)

A: Yellow-bellied Sapsucker Sphyrapicus varius. Slow tempo, double beats, slowing down during the last part of the drum. Continues for up to 3 to 4 seconds.

Sonogram - Pileated Woodpecker (2K)

B: Pileated Woodpecker Drycopus pileatus. Slow tempo, becoming faster and weaker towards the end of the drum. Lasts for more than one second.

Sonogram - Downy Woodpecker (2K)

C: Downy Woodpecker Dendrocopos pubescens. Slow tempo, the drum is shorter than one second.

Sonogram - Red-headed Woodpecker (2K)

D: Red-headed Woodpecker Melanerpes erythrocephalus. Fast tempo.

Sonogram - Red-bellied Woodpecker (2K)

E: Red-bellied Woodpecker Centurus carolinus. Fast tempo.

Sonogram - Hairy Woodpecker (2K)

F: Hairy Woodpecker Dendrocopos villosus. Fast tempo, the drum lasts for one second or more

Further, a bird can apparently indicate its emotional state. The birds vary their drums (a) by either different temporal arrangements of drums themselves, or different rates of drumming within each drum, to indicate species; (b) by differences in the length of the drum, to indicate sex and also (within different time brackets) individual recognition; and (c) by varying the rate of tapping within a drum to indicate emotional state. It is perhaps surprising that only within the woodpecker family has the beating of a tattoo evolved as a method of conveying messages.

Great Spotted Woodpecker Picoides major
drumming, recorded by William Pedley, 9 April 1978, Woodchester Park, Gloucestershire, England.

The other uses of the bill use only the mandibles. Frigatebirds Fregata sp. rattle their bills as an alarm note, white storks Ciconia ciconia indulge in bill clappering as part of the nest greeting ceremony. Owls young and old when approached at the nest snap their bills, creating a castanet-like sound; combined with a threatening posture, the sound is quite frightening.

To Europeans the best known user of bird wings as sound-producers is the mute swan. In flight this bird produces a humming throb not easy to describe, but highly distinctive and carrying for a considerable distance. It functions as a contact note. The existence of this instrument explains why the bird is called mute; unlike the other two European swans which are highly vocal, the mute swan uses its syrinx for very little because it has evolved a mechanical means of creating its contact note. As would be expected the Bewick's Cygnus bewickii and whooper swans C. cygnus make no functional noise with their wings; only the mute swan shows the specially shaped primary feathers that create the sound - as air passes over them, of course.

Mute Swan Cygnus olor
wings, recorded by Reg Tassell, 11 May 1978, Staverton Bridge, Devon, England.

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