ALPINE ANIMALS 493 



are alpine examples. Others, which require a year for development 

 in the lowland, require two in the alpine zone; Pieris callidice, for 

 example, is abundant in the Swiss Alps on alternate years. 7 The 

 lengthening of the larval period to one or two seasons has the result 

 that the emerging butterflies may exceed the lowland specimens in 

 size, the opposite of the usual size relations. Echinopteryx silesiaca 

 is such an enlarged (two-year) form of the lowland. E. pulla, and 

 Bombyx quercus var. callunae of the Riesengebirge is similarly a bi- 

 seasonal form of B. quercus. 8 Frogs may similarly be delayed in de- 

 velopment and pass a winter as tadpoles. 9 Small passerine birds which 

 normally raise two broods at lower altitudes raise only a single brood 

 at higher levels. 10 



Humidity.— The alpine zone in general has a more humid at- 

 mosphere than lower altitudes. Fog and clouds hang about the peaks; 

 moisture is condensed and precipitated by the rise of the air to the 

 cooler zone. Increased humidity is thus associated with high moun- 

 tains, though not necessarily so for all high altitudes, for the Tibetan 

 plateau and the Great Basin in western North America are extremely 

 arid, robbed of moisture by the surrounding mountain ranges. The 

 storage of precipitation as snow, and the relatively short season during 

 which melting takes place, provide abundant and uniform soil moisture 

 in the alpine zone. 



The melanism of many mountain animals appears to depend on this 

 increased humidity. Alpine insects, especially, tend to melanism. This 

 is notably true of beetles of the families Chrysomelidae and Cara- 

 bidae. 11 ' 12 The appearance of black forms at high altitudes in Lepi- 

 doptera has been observed in the Alps, the Andes, and in New 

 Zealand. 13 - 14, 15 Melanism or dark coloration is notable also among 

 mountain vertebrates. Salamandra atra among salamanders, Lacerta 

 vivipara among lizards, and Vipera berus var. prester among snakes, 

 illustrate this phenomenon in the Alps. Various rodents and other 

 mammals are darker at high altitudes or have melanistic varieties 

 which predominate in the alpine zone. 1G - 17 This does not seem to be 

 true of birds, certainly not with the pheasants of central Asia, where 

 many birds exhibit a tendency toward blue and violet coloration, 

 but not to melanism. 18 Dark coloration, by its absorption of radiant 

 heat, may be even more important to alpine animals perhaps in asso- 

 ciation with protection from the increased proportion of ultra-violet 

 radiation. 19 



Wind. — Strong winds are frequent in high mountains. Animals of 

 weak flight are adversely affected by such winds, for they are likely to 



