Page:The British Warblers A History with Problems of Their Lives - 4 of 9.djvu/71

 Thus far we have a clear case, since we are more or less guided by actual experience, but the subject now enters a more difficult and at the same time more speculative stage. I have referred to the great divergence in the song of the Lesser Whitethroat in Hungary, when compared with that in our Midland counties, and what we have to consider more particularly is how this change has been brought about. For this purpose it will be sufficient to confine ourselves to this one species, although it must by no means be thought that this is an exceptional case; other instances could be given showing quite as remarkable a variation. Now the influence of climate is no doubt considerable, but it is incredible that it can be so potent as to cause an immediate transformation each recurring season in the song of each individual migrant upon arrival at its destination; for this would not only imply an alteration upon its finally reaching its goal, but a continuous process of change from the moment it left its winter home.

The Lesser Whitethroat, like the majority of our summer migrants, winters in Africa, and in the spring migrates northwards to its breeding territory, in some cases passing over a great portion of Europe on its way thither; consequently we should have to assume that in every country, in almost every district, through which in its wanderings it would be compelled to pass, it would be gifted with a different voice and a different song, which is beyond belief. And if it be asked whether it is not possible that the change is produced gradually throughout the season, we can, fortunately, be guided in our reply by actual experience; for it is an observable fact that no appreciable change does take place during the season; the song of the Lesser Whitethroat is the same both as regards type and tone upon the first day of its arrival as it is one or two months later, excepting as regards the gradual deterioration in quality, which is common to all species whose vocal powers are highly developed, and is a different matter. If, therefore, we are right in concluding