168 



Biology in America 



cerning them. On alpine summits of the Rocky Mountains 

 and Sierra Nevada however one meets with several more or 

 less characteristic species. Here the marmot's whistle and 

 the sharp call of the pika or mountain hare, mingled with 

 the harsh note of the leucosticte, and the pipit's plaintive call 

 are carried across the barren slopes by the rush of the wind. 

 Here too is the home of the ptarmigan, whose changing fash- 

 ion with the changing season white in winter, mottled black, 



TIMBER LINE IN THE ROCKY MOUNTAINS 



Alpine firs at 11,000 feet altitude on Long's Peak, Colorado. From 

 "Plant Indicators. " 



Courtesy of Doctor F. E. Clements and the Carnegie Institution. 



buff or white in summer matches them so closely with their 

 background, that one stumbles upon them before he is aware 

 of it. The birds seem to realize their protection, for they 

 are very tame and may sometimes be killed with a stick or 

 stone. This tameness is however more likely due to infre- 

 quent molestation. The ptarmigan is also a characteristic 

 member of the arctic community nesting on the tundras of 

 the far north, together with the little lapland longspur and 

 the snow bunting, whofie change of coat in spring and au- 

 tumn resembles that of the ptarmigan. Even the gauzy- 



