SENSORY ADAPTATIONS OF BATS. 1 51 



Data on the daily movements of bats are still very meager. 

 Moffat ('05), who has observed Irish bats, states that among the 

 Irish bats, Daubenton's, the pipistrelle, and the long-eared fly all 

 night. The Noctule flies in the evening twilight, and the hairy- 

 armed flies for about an hour shortly after sunset, then retires to 

 its roost and again comes out shortly before sunrise. Six pipis- 

 trelles, living solitary, were found to have similar, and very reg- 

 ular habits, leaving the holes in hollow trees from ten to thirty 

 minutes after sunset, and returning from forty to eighteen minutes 

 before sunrise. The observations, which were made in August, 

 showed that there was no difference for warm nights and raw, 

 cool nights. Morao {'6t,) states that the bats in an immense 

 colony of Myotis lucifugiis in the attic of a house near Charles- 

 town, Maryland, were accustomed to leave their roost twice in 

 one night. His somewhat poetic statement that they left at 

 "the call of the whip-poor-will" cannot be considered accurate, 

 for in such a large colony, individuals could not be noted and 

 any general disturbance of the colony might be mistaken for a 

 renewal of the activity of the individuals. 



The same difficulty exists with regard to determining the daily 

 activity of bats in a cave. Their dwelling place is so large, and 

 the possible exits usually more than one, so that their movements 

 cannot be watched. It is possible to go into the cave and exam- 

 ine individuals, but there is the danger of disturbing them and 

 causing them to leave sooner than they would if unmolested. 



I have seen bats flying in the cave at all hours of the day and 

 night, and have also found them at rest there at all hours. Evi- 

 dently they may awaken from sleep at any time and fly to the 

 mouth of the cave. If the temperature and light are favorable 

 they go out and search for food. If it is cold or if the light is 

 too strong, they go back. If they are fat and well nourished 

 they settle down to another more or less prolonged period of 

 lethargy. But if the hunger is strong they are apt to remain 

 awake and active, or only go to sleep for a short time. 



The bats in the clusters seen in spring or late winter were usu- 

 ally awake and chattering. In the fall and early winter bats are 

 generally isolated and torpid. Those that are active are very 

 apt to reach the mouth of the cave as soon as conditions out of 



