MAMMALS OF THE REGION 115 



whole alimentary canal empty. This would indicate 

 unusual scarcity of food and a correspondingly light 

 deposit of guano. Bats are normally hearty feeders, 

 and some are known to eat a quarter of their own weight 

 of insects at a meal, and probably half their weight 

 or more during a night. They also drink heartily when 

 they first start out in the evening, flying to some pool 

 or open water and dipping repeatedly to the surface, 

 scooping up mouthfuls of water while skimming close 

 to the surface on widespread wings. 



Food is probably the determining factor in the abun- 

 dance and distribution of these bats, as they are said to 

 be more numerous some years than others, most so in 

 rainy years when insect life is abundant. Evidently 

 they move to find a satisfactory food supply, or leave 

 an area deficient in insect life. 



The details of their food habits are not well knowm, 

 as their teeth, with intricate cutting crowns, cut the 

 insects into minute particles. All of our United States 

 bats are known to feed entirely on insects, mainly 

 caught on the wing, but the kinds of insects in the 

 stomachs or composing the little dry droppings are 

 necessarily determined with great difficulty. Samples 

 of the guano from the cave proved under the micro- 

 scope to consist largely of remains of numerous species 

 of beetles and moths with occasionally recognizable bits 

 of wings, legs, or other remains of flies and other insects. 

 Bats shot while feeding at dusk sometimes have recog- 

 nizable insects in their mouths, but the relative pro- 

 portions of species eaten have never been determined. 

 Small, soft insects, such as mosquitoes, are rarely, if 

 ever, recognizable. 



