46 GLIMPSES OF INDIAN BIRDS 



aquatic birds. These are significant facts if we can 

 interpret them aright. I interpret them in the follow- 

 ing manner. It may be taken as a fact that every 

 species throws off occasionally white mutations or 

 sports, which breed true, so that, if allowed to persist, 

 they form the starting point for new varieties and 

 species. As most passerine birds are small and preyed 

 upon by the raptores, white varieties among them 

 usually perish at an early age on account of their 

 conspicuousness. Thus there are very few white 

 passerine birds. The paradise flycatcher lives amid 

 thick foliage, and so is comparatively immune from 

 the attacks of birds of prey ; but even here it is note- 

 worthy that the hens are not white but chestnut in 

 colour throughout life, and the cocks have chestnut- 

 coloured plumage until they are two years old. As 

 the cock shares in the duties of incubation equally 

 with the hen, her failure to acquire white plumage 

 cannot be accounted for by supposing her to have 

 a greater need of protection. Finn has suggested that 

 the whiteness of the cock is a senile character ; that 

 it is the livery of old age. 



The majority of the non-passerine birds that are 

 altogether or mainly white are large and able to fight 

 well, so that they are comparatively immune from the 

 attacks of raptorial birds. The gulls and terns, al- 

 though small, fly so powerfully as to be equally safe. 

 In the case of birds which secure their food in the water, 

 whiteness is probably useful in rendering them less 

 conspicuous to organisms living in the liquid medium 

 than they would be were they coloured. 



