92 E VOL UTION OF BIRD- SONG 



It is notorious that animals which have similar 

 physical features are much more alike in the early 

 stages of development than when mature ; in short, 

 that in progressing towards maturity the young tend 

 to diverge from general types to special types. The 

 same progressive divergence is indicated in the voices 

 of most genera of birds. In fact, the cries of the 

 young of birds physically allied are more alike than 

 are the cries or the songs of adults of the same 

 species. The reader who wishes to prove this theory 

 will be enabled to do so by the following records of 

 family resemblance, in which danger-cries and call- 

 notes are the principal features discussed. I shall 

 therefore not deal with this theory by itself; and 

 the omission will avoid an extensive repetition of 

 instances which are mentioned in the following pages. 



The similarity between the cries of some few 

 species unrelated by physical resemblances (such as 

 the pink, pink cry of the great titmouse, which, as 

 Mr. A. Holte Macpherson informs me, is common 

 with that bird in a part of Scotland as it is in Kent 

 and in Gloucestershire and which is closely like the 

 pink, pink of the chaffinch) afford instances of 

 exception to the almost universal rule that the cries 

 of birds nearly related physically are more alike than 

 those of others which cannot be thus associated. 



