296 



The Bird 



forms entirel}' different, mid thought to be due soleh' 

 to the amount of moisture in the ground on which it Hves. 

 Very dark-coloured and veiT pale individuals live within 

 a few hundred yards of each other, in dry and swampy 

 situations respectively, each, it is said, keeping entirel}^ 

 to its own little beat. 



We are all fan iliar with the changes of colour due to 



Fig. 236. — Night hawk perching lengthwi.se on a fallen branch. 



age, as, for instance, in the young Rose-breasted Gros- 

 beaks, which are very different from the male parent, and 

 the young Bald Eagles, which lack the white colour of the 

 feathers of head and tail. Certain wild pigeons show 

 marked differences in colour patterns between the young 

 birds and the adults, and very good evidence of the gradual 

 evolution which must have preceded these changes is 



