How Birds Produce Song

Posted: Sat Mar 10, 2007 9:23 pm Post subject: Article on Bird Song

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Andy (NDoan) kindly refered me to a wonderful article on Bird Song by Gareth Huw Davies that I would like to share with you. The full article can be read at:

http://www.pbs.org/lifeofbirds/songs/

Extracts to provide a flavour of what the article is about, follows:


Quote:
Song allows the bird to "speak" better than any other family of creatures. It is the perfect medium for communicating over long distances, or when it is hard to see the singer - and the audience: for example at night or in dense vegetation.

Whatever the habitat, birds have a way of singing into it. When a bird sings, it can always be heard, even after it has moved out of sight. Sound travels in all directions; it can penetrate through or around objects.

But how do birds produce such a complex variety of notes? How do they sing non-stop for minutes on end without pausing to catch their breath?

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..... unlike our soundbox, which is situated at the top of the trachea, the bird's syrinx is set much lower down, at the junction of the two bronchi or air tubes leading to the lungs.

This means that the syrinx has two potential sound sources, one in each bronchus. The separate membranes on each bronchus produce separate sounds, which are then mixed when fed into the higher vocal tract. This complex design means that birds can produce a far greater variety of sounds than humans can.

Birds give the impression of singing in long bursts for minutes on end without catching their breath. But they actually do this by taking a series of shallow mini-breaths, which are synchronized with each syllable they sing.

However, birds must work hard to get their particular message across. There is a lot of competition in the avian choir.

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Birds use sounds that travel better in particular conditions. In forests sound bounces off trees and is absorbed by the leaves. Here a constant brief signal works best. If the intended recipients mishear it the first time, they will surely catch it again. Birds of the forest floor, such as antbirds and curassows, use low-pitched calls that will not be bounced off and distorted by the ground. Out in the plains species like the Savannah Sparrow favor the buzz. The buzz is a compressed message which carries over great distances in open areas, savanna and grassland.

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A human singer can use amplification to hide his or her vocal deficiencies. But bird song conveys a very honest message about the singer. The singer can't cheat: because singing expends energy; smaller, weaker birds cannot bluff the receiver into thinking that it is a larger, stronger rival or mate. Only strong birds with extra energy and strength can invest the energy need for loud, continuous singing, and evade any predator that may detect it.

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Bird song has two main functions: to defend a territory and to attract a mate. Male birds do these things, so, throughout the bird world, it is usually the males singing the songs.

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