ANIMALS AS PASSIVE MEMBERS (COACTEES) 133 



some of them are strictly so. Practically all of them live in burrows 

 or dens, more rarely in hollow trees, but only a few, such as the badger 

 and the common skunk, hibernate to any considerable extent. 



As would be expected, the prey of a carnivore is determined largely 

 by relative size and activity, and by the habitat, the choice of which 

 often has some connection with food preference or amount. Thus, the 

 cougar kills deer, elk, mountain sheep, and antelope for the most part, 

 while the foxes and coyotes are largely confined in nature to animals 

 not larger than a jack rabbit or grouse, with emphasis on rodents. 

 The wolverine as the largest of the mustelids regularly catches animals 

 of the size of woodchucks and beaver, and is said to be able to pull 

 down caribou and moose on occasion, but its smaller relatives find the 

 rabbit and muskrat the upper limit in size. As a rule, the lesser 

 mammals and ground birds furnish the bulk of the food of carni- 

 vores, but this is supplemented by snakes, lizards, frogs, insects, car- 

 rion, and fruit, as well as by fish, crustaceans, etc., in some species. 

 The most completely carnivorous are the weasel and mink among the 

 smaller forms, and the gray wolf, lynx, and cougar of the larger ones. 



The snakes of North America are typically carnivorous, taking 

 chiefly small animals, none of them being known to eat fruit, which 

 is the nearest to flesh in texture. Two genera, the green and worm 

 snakes, are mainly insectivorous, with the addition of earthworms in 

 some instances. However, the great majority restrict their food to 

 larger forms and differ chiefly in the degree of preference for warm- 

 er cold-blooded animals. 



It is evident that the carnivores may exert a telling effect upon the 

 number of herbivores and through this upon the composition of the 

 biotic community. The relation is necessarily reciprocal and involves 

 the whole question of dynamic balance in nature, which is discussed 

 in the following chapter. Connected with this is that of the indirect 

 effect upon the plant matrix as a consequence of the destruction of 

 herbivorous rodents on a large scale. Campaigns of eradication of 

 flesh-eaters fail to reckon with these complex relations and have some- 

 times brought about an actual increase in rodents, usually detrimental 

 to the human interest that prompted the destruction of the carnivores. 



Carnivorous birds are not separable from mammals on the basis of 

 any coactional effect, but stand out by themselves on account of their 

 flight and special methods of securing prey. The vultures may be con- 

 sidered exclusively carrion-feeders, a habit in which they are joined 

 by the caracara and the bald eagle. The hawks and owls exhibit less 

 difference than would be expected in view of the nocturnal habits of 

 the owls, though these must be reflected to a considerable degree in 



