I may here say that by the word "call notes," I refer to everys note belonging to a species thai is not actually the song, although they are not by any means in a number of cases call notes in a literal sense. The climate in Sark and in the west of Donegal are much the same. The rainfall of both is above the average; both are subject to bad sea fogs from the Atlantic, and are therefore very damp. On the other hand, the climate of Worcestershire is peculiarly dry, the rainfall being much below the average. Looking, then, at this fact, that a lower pitch corresponds with a damp climate, and a higher pitch with a dry climate, I think I am justified in coming to the conclusion that clmate exercises a certain influence on the pitch of the notes and songs of certain species.
The dialectical variation is more difficult to explain, and my observations up to the present time are, comparatively speaking, so small, that perhaps I am hardly justified in forming any definite conclusion. The great difficulty in any researches on this point appears to be this—that all observations must be carried out by the same person; and to compare, except on general lines, with anyone making similar investigations is almost a practical impossibility. At first I was inclined to think that the song was more highly developed, or the reverse, in certain districts than in others, and that as a result of there being a scarcity of one sex or the other, sexual selection might exercise considerable influence in this direction; but on finding, after making further investigation, that migratory species were subject to this change, any theory with regard to sexual selection acting in this manner becomes impossible, and we must, therefore, look to some other cause for an explanation. I found that the song of the Whitethroat on the shores of Loch Lomond differed very much from anything I had previously or since heard. Again I noticed the same change in the call note of the Chaffinch in Inverness; and I now feel convinced that there are as many dialects amongst certain species as there are amongst human beings. I am inclined to think that the explanation will again be found in climatic influence, and that these dialects are in a great measure due to the lowering of the pitch. Take, for instance, the song of the Wren in a damp climate. When listened to very carefully, it will be be found that the parts that
