152 TEE POPULAR SCIENCE MONTHLY 



interior chambers of the caverns, half a mile or more from daylight, 

 and not, as a rule, in dense clusters, although thousands may be hang- 

 ing on a few square yards of rock. The positions of a number of bats 

 were marked on the roof of a low chamber early in October. A week 

 later about one third had moved, two weeks later half had moved and 

 at the end of a month not one remained in its original position. By 

 the end of December this chamber was entirely deserted and its occu- 

 pants were scattered and were, for the most part, in higher chambers, 

 where they were difficult of access. 



The first week in January was very warm, and at this time I found 

 many of the animals clustered near the cavern entrance. There is little 

 doubt that some of them went outside, but they are unfitted for securing 

 food that is cqncealed and they probably found few, if any, insects on 

 the wing after nightfall. A sudden drop in temperature a week later 

 was accompanied by a rush of cold air into the caves, and this scattered 

 the bats and sent them into the inner recesses where the temperature is 

 very nearly constant the year round. During February they again be- 

 gan to congregate near the entrance and the numbers increased and 

 diminished irregularly until late in April, when they rapidly dimin- 

 ished as the bats left the cave for the season. 



This, in brief, is the winter life of the cave bats. It begins, with 

 some individuals, in August but is interrupted before winter begins. 

 During the winter they move about to some extent and become more 

 restless at the approach of spring, but are not able to get any consider- 

 able quantity of food until warm weather begins in earnest, usually 

 in April. 



The torpid condition of hibernation is induced by abundance of 

 food and is not dependent on cold weather. The animals can be awak- 

 ened from their lethargy at any time by mechanical disturbance alone. 

 They are also made active by hunger after most of their fat is ab- 

 sorbed, but the end of their fast is determined directly by food supply 

 and indirectly by weather conditions. 



The Thirteen-lined Ground-squirrel 

 This animal is an inhabitant of the upper Mississippi Valley from 

 Indiana to the Eocky Mountains. It is better known as the " striped 

 gopher " but the gophers are very distinct, zoologically, while this spe- 

 cies, as its name implies, is a squirrel. 



It is closely related to the familiar chipmunk of the east, which it 

 resembles in size and habits, although it is more slender of build and 

 differently colored. In the region where it abounds it lives on the 

 lawns, in the orchards and pastures, along railway embankments, and, 

 in fact, almost everywhere. Hence it is easier to study than the chip- 

 munk, and this is the reason for selecting it in preference to the more 

 familiar eastern animal. 



