NO. 7 PROTFXTIVE ADAPTATIONS McATEE I35 



them, especially upon mice and i^round squirrels. The bob cats or 

 lynxes are fond of mice, ground squirrels, rabbits, and other rodents, 

 occasionally prey upon small domestic stock, and are known to eat 

 skunks and porcupines. The mountain-lion specializes upon deer, but 

 eats a variety of wild mammals, including foxes, skunks, coons, porcu- 

 pines, and bob cats. House cats take mice, rats, moles, shrews, and 

 rabbits. Coyotes and wolves prey upon the young of deer and 

 domestic stock, and upon prairie dogs, spermophiles, and other small 

 rodents. On the bill-of-fare of our various species of foxes are shrews, 

 mice, ground squirrels, pocket gophers, kangaroo-rats, and rabbits. 

 Badgers also take all of these mammals and in addition, prairiedogs 

 and mountain-beaver. The black-footed ferret is a special enemy of 

 the prairiedog, and relishes rabbits also. Weasels are ferocious 

 enemies of small mammals in general, and for their size, shrews are 

 fiendish predators. They commonly overpower and devour other 

 shrews and mice of their own or even of slightly greater bulk. The 

 polar bear preys especially upon seals, and the killer whales also 

 destroy these animals, as well as wearing down and devouring the 

 largest of all mammals, whales. 



Discussion. — Limitations due to relative sizes allowed for, we see 

 the same phenomenon in the case of mammals as in those of other 

 elements of bird food, namely that the more available (this usually 

 meaning abundant) groups are preyed upon most extensively, while 

 those which are less abundant or whose habitat is somewhat out of 

 the domain of birds are not so often captured. We see that the 

 burrowing moles and pocket gophers escape with moderate losses, but 

 that the abundant mice, and the both common and relatively easier 

 found rabbits suffer severely. It is evident also that the mammals 

 outside the range of prey of birds have serious enemies, chiefly other 

 mammals ; and it is further evident that, taking all mammal enemies 

 into consideration, they are most numerous in the case of so abundant 

 and ubiquitous a group as the mice, and proportionally less numerous 

 for other less abundant families. 



DISCUS.SION 



Availability -is a mighty factor in the choice of food by birds. 

 Within the limits imposed by special habitats, bodily modifications, 

 and the relative sizes of predator and prey, birds are prone to feed 

 upon what is abundant and easily obtained. Not only is this very 

 natural procedure the everyday order, but it is conspicuously exempli- 



