ADAPTATIONS TO HIGH ALTITUDES 53 



inactivity. They pass into a state in which they can 

 fast without feeling the worse for it; they lie low with 

 dulled sensitiveness instead of fretting themselves to 

 death in a hopeless struggle with the cold scarcity. 

 But we must not think of individuals trying to do this, 

 or, as it were, stumbling into doing this; we are face 

 to face with a slowly wrought-out adaptation which 

 has been a success. Certain constitutions, handi- 

 capped by a certain imperfection, have survived be- 

 cause of their ability to sink back into inaction and a 

 certain amount of coldbloodedness, and because of 

 their innate shrewdness in seeking out sheltered sleep- 

 ing-berths. In our " Biology of the Seasons " we 

 have discussed this interesting problem in detail. 



But we cannot leave the sleeping Marmot, a typical 

 Mammal of the mountains, without noting that, apart 

 from evading the severity of the winter, the hiberna- 

 tion pays in giving the creature a long rest a rest 

 even from eating. This long rest, like a very long 

 sleep to an overworked man, gives a chance to pro- 

 cesses of rejuvenescence to stave off that senescence 

 which is the universal and apparently inevitable tax 

 on structural complexity. 



Birds do not hibernate, partly because their warm- 

 bloodedness is so perfect, partly because their feathers 

 fit so closely, and partly because those that "feel the 

 cold " evade the winter by migration. There is no 

 doubt that some of our resident mountain birds, like 

 the Red Grouse, come lower down in winter; and the 

 Curlews leave the snow-covered moorland for the 

 low-lying fields and the seashore. We sometimes see 

 half a hundred Curlews at a time working among the 

 jetsam strewn on the beach. 



