EVOLUTION OF BIRD-SONG 



tinguish its song, are represented in another bird, 

 the wood-warbler, which, in the breeding season, cries 

 a repeated full whistle, kew^ kew, kew, seemingly as 

 a signal of danger. 



The mistle- thrush is an imitative singer, but its 

 imitations are never uttered with a full voice : they 

 are only heard after the full notes have been con- 

 cluded, and they are uttered in a much softer tone, 

 so that a listener cannot distinguish them unless he 

 occupies a position fairly near the singer. They are 

 often very good imitations. The blackbird also is 

 slightly imitative ; and in him, again, the imitations 

 are most often (though not always) uttered after the 

 full tones have ceased, when they form a continuation 

 of the phrase. It is in the brown thrushes that 

 mimicry is most evident — in the American mocking- 

 bird and catbird, for instance, as Wilson has so well 

 recorded. The common song -thrush is the most 

 imitative of its tribe in the United Kingdom. It 

 sometimes sings short phrases composed only of 

 whistled notes repeated, sometimes several times 

 successively, in the same intervals of pitch ; but 

 these short phrases are at once distinguishable from 

 the much longer and more irregular phrases of the 

 blackbird, which also are of a fuller tone. The first 

 songs of the young thrush and the young blackbird 



