CONTROLLED NATURAL SELECTION 



the males desert the females, they become, 

 by a post-nuptial moult, cryptically coloured. 

 It appears probable, therefore, that the male 

 coloration during the breeding season is for 

 the purpose of protecting the female. In the 

 other birds, the males assist in the rearing of 

 the young and do not lose this conspicuous 

 plumage, by means of a post-nuptial moult. 



The following conceptions are thus arrived 

 at: 



1. The females are cryptically coloured be- 

 cause of the open-nesting habits. 



2. The males retain attracting coloration 

 for the purpose of protecting the young. 



3. The difference in colour between the 

 sexes thus arising, is also used during the 

 breeding season, for the purpose of protecting 

 the female. 



Three birds which present sexual differences 

 in colour, nest in closed nests : the Stonechat, 

 Whinchat, and House Sparrow (Table VIII). 

 In the case of the Stonechat and the Whin- 

 chat, it is probable that this nesting habit is 

 a recent acquisition, for they lay blue and 

 blue-green eggs, characteristic of open-nesting 

 birds, and not the white eggs usually laid by 

 closed-nesting birds ; further, although these 

 nests are domed, the covering is frequently 



