Page:Popular Science Monthly Volume 84.djvu/154

150 from his prolonged sleep probably depends somewhat upon the temperature, 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 woodchucks; 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 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 perhaps 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 observations.

A bat in normal sleep rests with head down, suspended by the pointed and curved claws which are hooked about some small protuberance, such as a rough place on the bark of a tree or a rough stone; the