THE SONG AND NOTES OF BIRDS. 107 



couraged and partially developed in certain di- 

 rections by the exercise of the female bird's 

 choice or partiality. 



The entire subject is a very enticing one, and one 

 that I feel convinced would well repay investigation. 

 A careful comparison of the song of individuals of 

 the same species especially such as are widely 

 distributed in different areas would probably lead 

 to important results. Another very significant fact 

 is the great difference in the songs of birds very 

 closely allied, as, for instance, between the Willow 

 Wren and the Chiffchaff, the Marsh Warbler and 

 the Reed Warbler, and many others. It would 

 appear that song alone can become a powerful aid 

 to the modification of species. As I remarked 

 in my Evolution without Natural Selection " If 

 certain females are charmed by any peculiarities of 

 plumage or colour in certain males, I can see no 

 reason why the same great law should not apply to 

 vocal sounds as well. If certain females showed 

 preference for certain males possessing a peculiar 

 variation of song, it is easy to conceive how in time 

 slight structural variations which those individuals 

 might present could be preserved, and in time 

 become constant characters through the absence of 

 intercrossing, just as in those species which may 



