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, Mimus patachonicus, a common resident species in northern Patagonia, on the Atlantic side, very abundant in places. He is a true mocking-bird because he belongs to the genus Mimus, a branch of the thrush family, and not because he mocks or mimics the songs of other species, like others of his kindred. He does not, in fact, mimic the set songs of others, although he often introduces notes and phrases borrowed from other species into his own performance. He sings in a sketchy way all the year round, but in spring has a fuller unbroken song, emitted with more power and passion. For the rest of the time he sings to amuse himself, as it seems, in a peculiarly leisurely, and one may say, indolent manner, perched on a bush, from time to time emitting a note or two, then a phrase which, if it pleases him, he will repeat two or three, or half a dozen times. Then, after a pause, other notes and phrases, and so on, pretty well all day long. This manner of singing is irritating, like the staccato song of our throstle, to a listener who wants a continuous stream of song; but it becomes exceedingly interesting when one discovers that the bird is thinking very much about his own music, if one can use such an expression about a bird; that he is all the time experimenting, trying to get a new phrase, a new combination of the notes he knows and new notes. Also, that when sitting on his bush and uttering these careless chance sounds, he is, at the same time, intently listening to the others, all engaged in the same way, singing and listening. You will see them all about the place, each bird sitting motionless, like a grey and white image of a bird, on the summit of his own bush. For, although he is not gregarious as a rule, a number of pairs live near each other, and form a sort of loose community. The bond that unites them is their music, for not only do