150 WALTER LOUIS HAHN. 



cold weather during April was accompanied by an increase in 

 bats which reached a maximum of 153 on April 20. Observa- 

 tions carried on during the same period at 2 (Fig. i), which is 

 another part of the same cavern, showed a variation in the num- 

 ber of bats near the entrance which almost exactly paralleled 

 that in Twin Cave, thus showing that the movements had some 

 common cause and were not wholly accidental. 



Apparently the movements have a definite relation to season 

 and temperature. The bats come to the mouth of the cave at in- 

 tervals throughout the winter, but these intervals are longer in 

 the early winter when the animals are fat and well nourished. 

 The unusually warm weather prevailing early in January may 

 have acted as a stimulus for them to remain near the entrance ; 

 no doubt some individuals left the cave at night in search of food. 

 Cold weather followed and the cold, entering the cave, drove the 

 animals back to the w^armer parts. However the hunger stimulus 

 was becoming stronger and the bats came to the entrance more 

 frequently and tended to remain there. The maximum number 

 was reached with a moderate temperature, and when the weather 

 became quite warm the animals left the cave and did not all re- 

 turn but found temporary homes in trees and buildings. Cold 

 weather in April brought them back to the cave again, but most 

 of them remained near the entrance. When the weather again 

 became warm at the end of April, they left the cave for the 

 summer. 



Other observations were made on the movements of individual 

 bats at different times. The location and orientation of different 

 individuals were carefully marked and the place was visited 

 weekly. Out of 18 bats observed between November 19 and 

 December 3, 14 had moved within one week, and none remained 

 in the same place during two weeks. Later in the winter one bat 

 remained in the same spot near the entrance from February 4 to 

 27. Light reached the spot throughout the day and the tem- 

 perature remained near freezing point for several days at a time. 

 However, this was an exceptional case, as not many bats remained 

 in one location for more than four or five days during the latter 

 part of the winter. The small bat, P. sjibfiavus, is less active. 

 Its average period of staying in one place is about two weeks, 

 and one was noted in the same spot for 44 days. 



