i82 JUNGLE FOLK 



most practised eye cannot distinguish between the 

 cock and the hen. Nor does there appear to be any con- 

 nection between nesting habits and the presence or 

 absence of sexual dimorphism. The fan-tail fly- 

 catchers, in which the sexes are alike, and the paradise 

 fly-catchers, in which they differ widely, both build 

 little cup-shaped nests in the lower branches of trees, 

 and in both the cock shares with the hen the duty of 

 incubation. Again, the verditer and the white-browed 

 blue fiy-catchers build their nests in holes in trees ; 

 yet in the former both sexes are blue, while in the 

 latter the cock only is blue. 



Further, in the fly-catchers we see every gradation 

 of sexual dimorphism, from a difference so slight 

 as to be perceptible only when the sexes are seen side 

 by side, to a difference so great as to make it difficult 

 to believe that the sexes belong to one and the same 

 species. It must, therefore, be obvious to any sane 

 person that neither natural nor sexual selection can be 

 directly responsible for the colouration of many species 

 of fly-catcher. 



Another interesting characteristic of the fly-catchers 

 is the total absence of green in the plumage of any 

 of them. They are birds of a variety of colours ; 

 they display many shades of blue, yellow, orange, red, 

 grey, and brown, also black and white ; but not one 

 carries any green feathers. Yet they are essentially 

 arboreal birds, so that green would be a very useful 

 colour to them from the point of view of protection from 

 enemies. From the fact, then, that none of the fly- 

 catchers are green, we seem to be compelled to infer 



