BIRDS gj 



call, for bringing the male and female together, that is 

 peculiarly developed in most birds. 



From the pairing-cries, which were at first common 

 to the two sexes, there were gradually evolved sounds 

 that differed for each sex. This was effected by sexual 

 selection, which favoured those males that could make 

 themselves known at once as suitors to the heated 

 females. Quite a number of birds are still at the stage 

 of " sexually different notes." The grey wood-pecker 

 gives out his clear-ringing cry from the highest branch of 

 an oak, and is answered from afar by the different note 

 of his mate. Even the cuckoo is said to have different 

 notes in each sex. When it gives out, in ardent passion, 

 its trisyllabic cry " Cuck-cuck-cuck," we usually hear 

 shortly afterwards the continuous note of the female. It 

 is a sign that the love-message of the male has been 

 heard. 



Here we have reached the basis of song the special 

 call of the male and it will be asked how the further 

 development, up to the noble song of the nightingale, 

 came about. Again, however, we must depart from the 

 theories, as we have rejected "female choice." More- 

 over, the song is not mainly intended for the female, 

 since the male usually sings alone, and often, like the 

 blackbird, on the top of a tree, and so is easily seen; while 

 there is no female near to see him. But the song would 

 be just as unintelligible as a means of intimidation ; at 

 the most, we may assume that it has become so much 

 developed and specialised because it is useful to the 

 male to let his presence be known far around, so that 

 any unpaired companion may know from afar that the 



