EVOLUTION OF THE COLORS OF BIRDS. 269 



the brown plumage of the young would seem the best 

 suited. Neither can it be attributed to any known gen- 

 eral laws of growth, for why should these produce first a 

 brown plumage and afterwards transform it into a bluish 

 gray one? 



GENUS PARABUTEO. HARRIS'S HAWK. 



(2) Adult male like female; young with a peculiar 

 first plumage. 



Prevailing colors, dark brown, black, white. 



This is one of the genera which is comparatively free 

 from the workings of natural selection and is fast be- 

 coming melanistic. The white base and tip of the tail 

 in contrast to the black middle portion affords an excel- 

 lent recognition mark, which was perhaps originally dis- 

 criminative in its nature. The young are irregularly 

 marked as would be expected if the pigment was de- 

 posited without the guidance of natural selection. 



GENERA BUTEO AND ARCHIBUTEO. THE BUZZARDS. 



(2) Adult male generally like female; young with a 

 peculiar first plumage. ~ 



Prevailing colors, brown, rusty, gray, black, white. 



There is a general tendency throughout this group of 

 large and powerful birds, so well able to take care of 

 themselves, to become melanistic. Some species, in- 

 deed, have two phases of plumage, a lighter normal one, 

 and a melanistic one, which shade into one another 

 through every possible stage of transition. The red 

 color of the tail in B. borealis is a striking recognition 

 mark which can be seen at surprisingly long distances, 

 and may have been at first discriminative and afterwards 

 directive or socialistic in nature. The different geo- 

 graphical races of this species are largely the result of 

 the direct influence of the environment, together with 

 isolation. The same is true of the races of B. lineatus, 



