BRITISH WARBLERS
must have innumerable opportunities of hearing the cries, call-notes, and songs of species foreign to this country; yet they fail to incorporate them, to any appreciable extent, with their song.
The truth is, that much more evidence is required; it must not be forgotten that my facts are collected from, comparatively speaking, a very small area. It is possible that the sequence of imitative strains in the song of the male in other parts of the British Islands does not contain the songs of the species mentioned in so large a proportion, but I can scarcely believe that it can be so; it is more probable that the law of uniformity accompanies the imitative faculty, as it does every other vital manifestation of the animal world, and that for reasons at present unknown to us, certain strains may have been and may be incorporated more readily than others.
Returning once again to the simple explanation with which we set out, namely, individual acquirement, I find it difficult to understand from this point of view why there should be such similarity in the imitations; for with the imitative faculty so strongly implanted, and with different males living in contact, as they undoubtedly do, with different species, we should here look for and surely expect to find some traces of divergent individualism.
There is yet another method by which they may have arisen, although, as we shall see, not a very probable one. Many naturalists believe that the type of the song of different species is a matter of tradition, that is to say, that the parents hand it down to their offspring. This hypothesis requires that the young birds should have had predominant opportunities of hearing their parents' song; but the fact seems to have been lost sight of that there are species, and those, too, in which the vocal powers are developed in the highest degree, that are silent during the period in which they are engaged in tending their young, some of them even remaining so until the following spring. The power of imitation must be founded upon a congenital basis, and if the song had been thus handed
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