COMMUNITIES IN DRY, OPEN LANDS 457 



{Cricetus) in Eurasia and ground squirrels {Citellus) in both Eurasia 

 and North America store grains and other food material. Ochotona 

 dauricus, of the Asiatic steppes, gathers haystacks up to a weight of 

 10 kg. in the vicinity of its burrows. Birds which were for the most 

 part summer visitors have disappeared; but in the Gobi region, where 

 little or no snow falls, larks and buntings overwinter in spite of tem- 

 peratures as low as — 37° if sufficient grass seed and other food is at 

 hand. 37 



The large mammals are less affected by the cold; they have a rela- 

 tively small surface and because of their strength are able to carry an 

 enormously thick winter coat of fur. They eat twigs and dry leaves, 

 and scrape dry grass, lichens, and moss out of the snow. The bison 

 of the North American plains, the yaks and wild camels of the high- 

 lands of Tibet, defy the winter. Many mammals are nevertheless com- 

 pelled to migrate. Antelopes and wild ass {Equus hemionus) leave the 

 wintry Gobi, not on account of the amount of snow, but because the 

 water is frozen; thirst, not cold, forces them to depart. The prong- 

 horned antelope of North America migrates to places where grazing 

 is good, often many hundreds of kilometers distant, and overwinters 

 there in large herds; the open plains are made well-nigh uninhab- 

 itable for them by the snow storms. The bison, too, used to wander 

 some distance southward, but without thereby getting out of the 

 range of the snowy winter; through use during innumerable years, 

 the buffalo paths in places became almost as deep as the animals were 

 tall. Vast numbers of bison existed on the Great Plains, up to the time 

 of the building of the transcontinental railroads. The great number of 

 skulls and other remains of bison which have been discovered in 

 northern Colorado and Wyoming are thought to be the remains of 

 herds that perished in blizzards. 38 Now all have been exterminated by 

 man save an insignificant, protected remnant. 



Following a snowy winter in the steppe, there is a slow revival in 

 the animal world as well as in the plant world, quite different from 

 the over-night awakening following the breaking of the dry season 

 described above. The temperature rises slowly, grass and herbs spring 

 forth, the hibernators awaken, insects develop, the migrating mammals 

 and flocks of birds return. 



If we make a comparative survey of the steppes, we find that in 

 the small steppe areas, like those in Spain, characteristic steppe ani- 

 mals are lacking, even though a number of characteristic plant forms 

 have developed in them. The inhabitants of such areas are species from 

 the surrounding regions, species which are able to live in the steppe, 

 which is there characterized only by the selection of the animals and 



