CLASS MAMMALIA 683 



the body, but the fat masses stored up in the autumn are con- 

 sumed, 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 i, and does not come out until April i. 

 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 practically 

 all winter. Many other mammals hibernate for a greater or less 



period of time. 



e. 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, bison, bat, and lem- 

 ming. The fur-seals in American waters breed on the Pribilof 

 Islands in Bering Sea, where they remain from about May i to 

 September 15. They then put out to sea, spending the winter 

 months making a circuit of about six thousand miles. 



The reindeer of Spitzbergen migrate regularly to the central 

 portion of the island in summer and back to the sea-coast in the 

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

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

 and fall migrations; they covered an area of about thirty-six 

 hundred miles from north to south, and two thousand miles from 

 east to west. 



The lemmings of Scandinavia (Fig. 524) are celebrated for 

 their curious migrations. They are small rodents about three 

 inches in length. 



" At intervals, averaging about a dozen years apart, lemmings 

 suddenly appear in cultivated districts in central Norway and 



