156 EVOLUTION OF BIRD-SONG 



individual wood-thrush that he could recognise him 

 above his fellows the moment he entered the woods 

 {pp. at. p. 291). 



Variation in song is most noticeable at the end 

 of the phrase, the first parts of phrases being more 

 like common types than are the later parts. This is 

 most observable in birds which do not imitate very 

 much, nor greatly vary the character of their song ; 

 such are the nightingale, which so often preludes its 

 song with one of its call-notes ; the chaffinch, which 

 particularly varies the two last syllables of its song ; 

 the greenfinch, which always commences a phrase 

 with a rapid repetition of its titit call-note ; the 

 willow -warbler, which follows the same course of 

 proceeding, and varies its sweet phrase towards the 

 close. The reed-warbler seems to commence each 

 phrase in much the same manner, and even the 

 sedge-warbler often exhibits this method. I think 

 we may safely say that the songs of all birds which 

 can be said to sing become extended during the 

 season of song, though the extension be but slight, 

 as in the chaffinch, or the variation be merely an 

 extension of an interval of pitch between certain 

 notes, as occurs in the cuckoo. The phrases of the 

 robin, starling, blackbird, thrush, brown wren, lark, 

 redstart, yellow bunting, blackcap, lesser whitethroat, 



