I30 GLIMPSES OF INDIAN BIRDS 



them are characterised by short legs and broad toes. 

 These are adaptations to the arboreal habit, in the 

 formation of which natural selection has, in all proba- 

 bihty, played an important part. The habits of all 

 the genera are identical. They, one and all, build 

 the rough-and-ready shakedowns which do duty for 

 nests amongst the Columhidce. All lay the inevitable 

 two white eggs. Yet the sexes of the genus Crocopus 

 are alike in external appearance, while those of the 

 genera Osmosteros, Sphenocercus, and Treron exhibit 

 considerable dimorphism. Again in the genus Butreron 

 the sexual differences displayed are inconsiderable. 

 These facts, of themselves, are quite sufficient to 

 disprove the theory that sexual dimorphism in birds 

 is due to the hen's greater need of protection. Cock 

 green pigeons assimilate so well to their leafy en- 

 vironment that there cannot possibly be any necessity 

 for their wives to be differently dressed. Further, it 

 is worthy of note that the most flourishing of the 

 genera of green pigeons is that in which the sexes 

 dress alike. 



