Page:The British Warblers A History with Problems of Their Lives - 3 of 9.djvu/61

 facts, and the analogy of the deterioration of the colour and plumage as a result of the same cause, and that the development of the vocal powers in the spring corresponds with that of the sexual organs, showing how intimately associated the one is with the other; bearing all this in mind, we can with some confidence say that the deterioration, such as we find, is the very result that we should under the conditions anticipate.

(3) Imitation forms a large part of the vocal efforts of the males, and in this respect I have been able to detect little difference between immature and adult birds. In both cases the imitations are very perfect and unmistakable. Many of them are the immediate copies of sounds produced by members of other species; for instance, when a Blackbird utters its alarm-note, a male will sometimes at once repeat it note for note, or when some other species not far distant, such as a Redstart (Ruticilla phoenicurus), happens to sing, he will pause in his song and then reproduce a repetition of the sound. This demonstrates how acute their sense of hearing is. But the greater part of this imitation is produced from memory, as is amply shown by the song of the males early in the spring before the species imitated have arrived. Those most frequently copied are the Nightingale and Garden-Warbler, but I have heard in addition to those already mentioned, imitations of the Whitethroat, Sedge-Warbler, Starling (Sturnus vulgaris), Thrush (Turdus musicus), Linnet (Acanthis cannabina), Great Titmouse (Parus major), Long-tailed Titmouse (Acredula caudata), Missel-Thrush (Turdus viscivorus), and Tree-Creeper (Certhia familiaris).

The sequence of imitative strains does not appear to be always similar in the same individual; the various imitations being utilised anyhow, the same one is often repeated, and some are made use of much more frequently than others. When, upon further investigation, we attempt to find a solution of the method by which these imitations have reached the