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Pretending To Be A Bird

May 24, 2004

Tape-recorders allow us to record and analyze birds' singing, but communicating with birds is more difficult.

From time immemorial, people have listened to the birds singing, recognized birds by voices, have been able to guess their condition. Some people are able to successfully imitate bird's singing. Only in the 50s of the last century, researchers managed to put the matter on a strictly scientific basis, when the tape equipment became available. Researchers started to record birds' sound signals and to analyze their frequency and rhythmical peculiarities. B.M. Zvonov, specialist of the Severtsov Institute of Ecology and Evolution Problems, Russian Academy of Sciences, has spent more than 30 years on this investigation. He analyzed the mechanism of creating alarm signals and breeding songs of multiple bird species and came to the conclusion that all signals were based on common principles, the knowledge of which allows to communicate with birds and to control their behavior.

Let us take fledgings, for example. They give sound signals so that the parents would not forget about them. Each species has individual frequency characteristics of this squeak. When fledgings are fed up and happy with life, their pipe is rhythmical. That signals for proper order. Once a baby bird gets hungry, it starts to signal much more frequently, this being a common pattern for all investigated bird species. The parents, when they hear a more frequent 'yells' of their baby, rush feeding and protecting it.

Adult birds sing during the nesting period to mark up their territory. B.M. Zvonov analyzed singing of two species - lanceolated warbler (Locustella lanceolata) and grasshopper warbler (Locustella naevia). These birds bear close resemblance with each other, besides they live side by side. In such cases, a song is nearly the sole opportunity to distinguish the species. The record analysis showed that breeding signals of both species are based on the same principle - the males use rhythmical succession of coupled syllables parted by a time gap. However, individual syllables in the breeding song of the grasshopper warbler are shorter than those of the lanceolated warbler, and the frequency of syllable succession is one and half times higher. These rhythmical peculiarities allow to determine the species the singer belongs to.

During the breeding period, some species have distinct territorial delimitation, and each male is flying over its territory and singing its species song, thus marking up the boundaries of its lot. To a human ear, all songs seem similar, however, each male sings an individual song, thanks to which it "pegs the lot". As a rule, the above differences are reached due to peculiarities of rhythmical structure of singing, but not due to the frequency range. Along with that, each male manages to preserve rhythmical pattern specific for its species.

All principles "used" by the birds in their communications were also accepted by people. The most well-known example is decoys, with the help of which the hunters call to the birds. All decoys are based on the simple principle - they are to provide the required frequency range, and the hunter's breath ensures the needed rhythmical pattern. However, the decoy use is the art to a large extend. The record analysis allows to translate rhythmical and frequency peculiarity of each song into digits and based on precise knowledge to build birds' signals synthesizers. These synthesizers help to frighten away or to call to birds not only for hunting purposes, but also for counting, feeding or observation. However, interested persons can mention a number of other situations, when they would like to "talk" with birds. The equipment would even allow to pretend a quite definite bird or two birds and to carry on a lively dialogue between them.

Informnauka (Informscience) Agency