122 RELATION OF SONG TO THE TERRITORY 



cliff we cannot distinguish between the voices 

 of different individuals. And the more highly 

 developed the song, the greater the range of 

 variation appears to be ; but notwithstanding 

 this — notwithstanding the fact that the pitch 

 may differ, the phrase combination may differ, 

 and the timbre may differ — the song remains 

 nevertheless specific. So that the two principal 

 features of "song," broadly speaking, are 

 "diversity" and "specific character." 



In contrast with the call-notes, the majority 

 of which can be heard at all times of the year, 

 the song is restricted as a rule to one season, 

 and that one the season of reproduction. It 

 is true, of course, that some birds sing during 

 the autumn, and, if the cUmatic conditions are 

 favourable, in the winter also, just as others 

 betray, in the autumn, symptoms of emotional 

 manifestation peculiar to the spring ; but just as 

 the manifestation of the latter is feeble and 

 vestigial, so, too, does the song of the former 

 lack the vigour and persistency which is charac- 

 teristic of the spring. Again, in contrast with 

 the call-notes, which are common alike to both 

 sexes, song is confined to one sex — a peculiar 

 property of the males. 



Now all, I think, will agree that it must 

 serve some biological purpose — this at least 

 seems to be the conclusion to be drawn from the 

 two outstanding features of "diversity" and 

 " specific character " ; and since the voices of 

 different individuals of the same species vary, it 

 has been suggested that, by creating a more 



