112 



COACTION: THE INTERRELATIONS OF ORGANISMS 



vegetation for nesting. In game management, diversity of cover suited 

 to the various needs favors large populations. 



The small non-burrowing mammals select various types of cover. 

 The snowshoe rabbit prefers a small woody growth so thick that foxes 

 and wolves cannot travel through it with ease. The desert plains 

 blacktailed jack rabbit finds shelter in the mesquite and buck brush 

 and may seek food at some distance. Larger animals also seek 

 shelter in vegetation; the moose frequents dense coniferous forest in 

 winter and hides the young in alder thickets. The great cats, such as 



Fig. 25 



Fig. 26 



Fig. 25. — Ravens {Corvus corax sinuatus Wag.) build a nest of old barbed wire 

 in the "Dust Bowl" where other materials are scarce; Dalhart, Texas; 1935. 



(Photo by Edith Clements.) 

 Fig. 26. — Nest of a lark sparrow {Choiidestes grammacus strigatus, Swains.) 

 made of grasses in mixed prairie near Scotts Bluff, Nebraska. (Photo by 



Edith Clements.) 



the jaguar (Bailey, 1931), commonly take refuge in brush thickets. 

 Small rodents, notably Microtus, hide in the grass cover, making run- 

 ways from place to place. Many small ground birds, particularly 

 those nesting in swamps and low ground, take full advantage of the 

 vegetative cover in selecting nesting sites. Even the burrowing mam- 

 mals such as some species of kangaroo rats and ground squirrels prefer 

 to burrow under shrubs, while the nine-banded armadillo selects the 

 center of a thicket or a group of trees for its burrow. 



The importance of shelter has further been brought out experi- 

 mentally by Gause (1934), who found that paramecia are able to 



