414 PRACTICAL ZOOLOGY 



cold. They therefore seek a sheltered spot, such as a burrow in 

 the ground, in which to spend the winter. Furthermore, at this 

 time the fur of mammals is very thick and consequently helps 

 to retain the body heat. 



The temperature of the body of hibernating animals becomes 

 considerably lower than normal; for example, a ground squirrel 

 which hibernated in a temperature of 35. 6° F. had a body tem- 

 perature exactly the same. Respiration almost ceases; the heart 

 beats very slowly; and no food is taken into the body, but the 

 fat masses stored up in the autumn are consumed, and the animal 

 awakens in the spring in an emaciated condition. 



The woodchuck is the most profound sleeper of our common 

 mammals. It feeds on red clover in the autumn, goes into its 

 burrow about October 1, and does not come out until April 1. 

 The bear does not sleep so profoundly, for if there is plenty of 

 food and the temperature is mild, he will not hibernate at all. 

 When the bear does hibernate, he scoops out a den under a log 

 or among the roots of a hollow tree. The raccoon and gray 

 squirrel sleep during the severest part of the winter; the skunk 

 spends January and February in his hole; the chipmunk wakes 

 up occasionally to feed; and the red squirrel is abroad practi- 

 cally all winter. Many other mammals hibernate for a greater 

 or less period of time. 



Migration. — Comparatively few mammals migrate; this 

 may be due in part to their inadequate means of locomotion. 

 Among those that do migrate are the fur seal, reindeer, caribou, 

 bison, bat, and lemming. The fur seals in American waters 

 breed on the Pribilof Islands in Bering Sea, where they remain 

 from about May 1 to September 15. They then put out to sea, 

 spending the winter months making a circuit of about six thou- 

 sand miles. 



The reindeer of Spitzbergen migrate regularly to the central 

 portion of the island in summer and back to the seacoast in the 

 autumn, where they feed upon seaweed. The bisons used to 

 range over a large part of North America, making regular spring 



