150 THE POPULAR SCIENCE MONTHLY 



ing from his prolonged sleep probably depends somewhat upon the tem- 

 perature, but this remains to be proved. The earliest that I have 

 known ground hogs to come out was the third week in February in the 

 extremely warm season of 1907 in the region already referred to — 

 southern Indiana. They seemed all to emerge at about the same time, 

 for I saw a number of places where earth was thrown out of their holes 

 and their tracks were left in the soft clay, although it was two weeks 

 later before I saw any of the animals, for they are extremely wary and 

 active at this season. When they first break their long fast they are very 

 thin and eat twigs, grass or almost any tender herbage that can be 

 found. Perhaps it is on this account that they pay no attention to cold 

 when once out. In the year in question we had cold weather and several 

 inches of snow about two weeks after I noted the first signs of wood- 

 chucks ; but it failed to keep them in. Mating time is then at hand and 

 this, no doubt, is an additional incentive for them to remain active. 



Bats 



Bats are more numerous in tropical and subtropical countries than 

 in cooler climates. They do not hibernate there, although the presence 

 of large numbers of some of the species in certain caves suggests that 

 they may remain there for days at a time without going out to feed. 



Bats are capable of flying very rapidly for a considerable length of 

 time and it is not surprising that some species living in temperate 

 climates migrate southward in winter. As far as we know, this habit 

 is limited to three or four species in northern North America. These 

 have their summer homes in trees throughout the wooded region from 

 the Ohio River to Hudson Bay and migrate southward to spend the 

 winter in the Gulf States. Whether they also hibernate for a time, I 

 am unable to say. 



The most conclusive evidence of their migration is the fact that 

 they have never been found in the northern limits of their, range in 

 winter, and seldom or never in the southern limits in summer. In a 

 few instances their southward flight in early autumn has been observed. 

 The northern range of these migrating species is occupied by six or 

 eight other kinds of bats that are not known to migrate regularly. 

 These hibernate, chiefly in underground caverns, but sometimes per- 

 haps in attics, deserted buildings and stone walls. 



I have studied the hibernation of these animals in the limestone 

 caves of southern Indiana. Other species have been studied in Europe, 

 but what I shall say here is based almost entirely on my own ob- 

 servations. 



A bat in normal sleep rests with head down, suspended by the 

 pointed and curved claws which are hooked about some small protuber- 

 ance, such as a rough place on the bark of a tree or a rough stone ; the 



