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As all or most singing birds learn their songs from the adults of the same species, it is not strange that there should be a good deal of what we call mimicry in their performances: we may say, in fact, that pretty well all the true singers are mimics, but that some mimic more than others. Thus, the starling is more ready to borrow other birds' notes than the thrush, while the marsh-warbler borrows so much that his singing is mainly composed of borrowings. The nightingale is, perhaps, an exception. His voice excels in power and purity of sound, and what we may call his artistry is exceptionally perfect; this may account for the fact that he does not borrow from other birds' songs. I should say, from my own observation, that all songsters are interested in the singing of other species, or at all events,
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in certain notes, especially the most striking in power, beauty, and strangeness. Thus, when the cuckoo starts calling, you will see other small birds fly straight to the tree and perch near him, apparently to listen. And among the listeners you will find the sparrow and tits of various species--birds which are never victimized by the cuckoo, and do not take him for a hawk since they take no notice of him until the calling begins. The reason that the double fluting call of the cuckoo is not mimicked by other birds is that they can't; because that peculiar sound is not in their register. The bubbling cry is reproduced by both the marsh warbler and the starling. Again, it is my experience that when a nightingale starts singing, the small birds near immediately become attentive, often suspending their own songs and some flying to perch near him, and listen, just as they listen to the cuckoo. Birds imitate the note or phrase that strikes them most, and is easiest to imitate, as when the thrush copies the piping and trilling of the redshank and the easy song of the ring-ouzel, which, when incorporated into his own music, harmonizes with it perfectly. But he cannot flute, and so never mimics the black-
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bird's song, although he can and does, as we have seen, imitate its chuckling cry.
There is another thing to be considered. I believe that the bird, like creatures in other classes, has his receptive period, his time to learn, and that, like some mammals, he learns everything he needs to know in his first year or two; and that, having acquired his proper song, he adds little or nothing to it thereafter, although the song may increase in power and brilliance when the bird comes to full maturity. This, I think, holds true of all birds, like the nightingale, which have a singing period of two or three months and are songless for the rest of the year. That long, silent period cannot, so far as sounds go, be a receptive one; the song early in life has become crystallized in the form it will keep through life, and is like an intuitive act. This is not the case with birds like the starling, that sing all the year round--birds that are naturally loquacious and sing instead of screaming and chirping like others. They are always borrowing new sounds and always forgetting.
The most curious example of mimicry I have yet met with is that of a true mocking-bird,