THE MOUNTAINS 



359 



feathers sprinkled through the gray and brown ones he has 

 lately acquired. 



The danger from attack by Falcons, Goshawks, Snowy 

 Owls, and various predaceous mammals, to which the ab- 

 sence of cover in their environment exposes them, requires, 



American Pipit on Nest 



however, still further adaptations. In that physiological 

 cycle of events comprising the bird 's year, a complete re- 

 newal of the plumage by molt is required immediately after 

 the close of the breeding season, when the bird passes into 

 winter plumage. If, however, the Ptarmigan should follow 

 this custom, it would don its white garb before the coming of 

 snow and be rendered fatally conspicuous. In defiance, 

 therefore, of the laws of molt, the bird does not acquire the 

 usual winter dress, but a gray supplemental or supernumer- 

 ary plumage, evidently designed to carry it over the snow- 

 less period, from the end of the nesting season in late July 

 or early August, to the snows of September or early Octo- 



