68 EVOLUTION OF BIRD-SONG 



this theory. With the exception of the mono- 

 tonous songs of the nightjar, grasshopper-warbler, 

 and cirl-bunting, there are few which do not ex- 

 hibit this feature. Even the stock -dove's jerky 

 coo evidently becomes more vehement as his song 

 proceeds. 



6. Individual variation is generally to be per- 

 ceived, if at all, at the end of the phrase ; and 

 similarly, the first parts of the phrases sung by allied 

 birds have most resemblance to common types. 

 This may be observed in the whitethroat, lesser 

 whitethroat, blackcap, greenfinch, brown linnet, 

 lesser redpoll, siskin, sedge-warbler, reed-warbler, 

 and in the buntings. 



7. The alarm -cries and call -notes (which are 

 generally common both to males and females) of 

 allied birds are more alike than are their songs 

 which are almost invariably exhibited by males 

 only. 



8. The cries of allied young are more alike than 

 are the cries of allied adults. This, and the preceding 

 subject, will be considered in relation to divergence 

 from the general to the special as exemplified in 

 the voices of birds, and in the chapter on heredity. 



9. Only small birds properly sing. This is the 

 statement of Darwin, who mentioned the Australian 



