BRITISH WARBLERS
it then migrates to its breeding home. Assuming that its vocal powers lie dormant during the winter months, it is evident that when it reaches its destination in the spring it can have acquired no imitations, and therefore commences the period of sexual activity with its true song plus the imitative tendency undeveloped. Supposing, however, that the development of this faculty occurs at an earlier stage in the life of the bird than we are assuming to be the case, then the imitations ought to represent not only the songs of species that migrate to northern countries, but also the cries and call notes of those indigenous to the African continent. Now so far as an appeal to experience can be made, each male upon arrival is capable of reproducing the notes of other species, and, to a large extent, the imitations are of the songs of the birds of the surrounding district, but I cannot state definitely that any one individual to which I have listened was a bird of the previous season. In all. I have heard thirty-two different species copied, and no one male to which I have listened has reproduced the cries of more than seventeen. Of these thirty-two, no less than eleven are constantly introduced into the song of the males both in this country and in Holland; and of these eleven again the notes of the Blue Titmouse. Swallow. Starling. Linnet and Sparrow are habitually reproduced. They are the more common species of the surrounding neighbourhood, we may say, and consequently would be more liable to be imitated, but we must not overlook the fact that an instrument capable of copying such widely divergent sounds as the notes of the Blue Titmouse. Magpie. Starling and Green Woodpecker, and the song of the Nightingale, is qualified to imitate almost any sound to be found in bird life. How can we explain this similarity in the strains reproduced? Is there, as suggested in the life of the Blackcap, an innate proclivity to copy some sounds in preference to others? Until definite evidence is produced showing that the acquired imitation of one generation can become the congenital variation of the
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