BRITISH WARBLERS 



put forward that climate may exercise some influence upon 

 the vocal muscles irrespective of natural selection, and thereby 

 contribute towards the differences we discern. The problem 

 is a difficult one and recent observation adds to the complexity. 

 One wants to know whether it is an isolated phenomenon, 

 removed from the general course of evolution, or whether it is 

 linked with other physiological differences which we cannot 

 yet fully determine, though we are beginning perhaps to under- 

 stand them in part. As our knowledge of local races increases, 

 so the importance of this vocal variation looms large in our 

 field of inquiry. We cannot altogether disregard it. For 

 even if it could be shown that varying climates could exercise 

 differential effects on the vocal muscles, there would still 

 remain plenty of matter for debate. Is there such a thing in 

 song as a definite ancestral type ? And if not, at what period 

 in the life of the individual is the voice fashioned ? This is 

 the crux of the whole matter. I have suggested climate and 

 I still hold to it as a directing influence, because, if we regard 

 the facts presented as a whole, we find one feature which 

 arrests our attention and may almost be spoken of as universal, 

 namely, an alteration of the pitch in different districts ; the 

 farther we travel west — I am speaking of Europe — the more 

 we observe the phenomena in districts dominated by the 

 Atlantic, the lower we find the pitch becomes. If every 

 individual of the same species and in the same locality 

 presented this peculiarity in a similar degree, the matter 

 would be more simple. But this is not the case. Two 

 Chaffinches will utter their spring call side by side in Donegal, 

 both in a lower pitch than one is accustomed to hear in the 

 Midland counties of England, but the one so very much lower 

 as to make the possibility of recognition by other members of 

 the same species in other localities somewhat remote. With 

 the meagre facts at our disposal it would be unwise to attempt 

 to arrive at any decision. The phenomenon is probably part 

 of the larger problem of local races, but whether the delicate 

 adjustments which these slight differences imply are due 



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