Tuesday, September 11, 2007

The messages relayed in the dawn chorus

At daybreak on a May morning, the northern European woodland fills with the sounds of bird song. First a trilling blackbird call, then perhaps a thrush song. Slowly it builds up to a climax of trills, warbles and chirps as male birds stand on their song posts and lustily sing their parts in the dawn chorus. A songster has to be awake and singing as early as possible in the morning if it is to keep hold of its hard-earned territory.
To human ears this chorus of birdsong is powerful and varied, but the voice of each individual bird is virtually impossible to pick out. In the midst of the chorus, each bird sings its own song and listens for any intruders nearby, for each species can distinguish the individuals of its own kind.
A male pigeon, with its simple two-note call, is heard and understood by other pigeons. The other males know that he is laying claim to a patch of woodland, while the females recognise his advertisement for a mate.
When starlings gather early in the evening, and again just before they part in the morning, each bird chatters until the noise level rises to a grating peak. It is not known why they do this, though it may be to coordinate the gathering and movement of the colony in and out of the roost.

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