BATS 53 



bats from the Yosemite region numbers only 80 specimens, most of these 

 being of 2 of the 9 species represented. 



The wing of a bat is a thin elastic double membrane or skin which 

 stretches between the greatly elongated 'fingers' of the forelimb and 

 between the fifth of these and the body of the animal. The hind limbs and 

 tail are included in this flight membrane so that the total expanse when 

 extended is many times that of the body alone. By moving the forelimbs 

 the bat is able to fly, and its passage through the air seems much better 

 controlled than in the case of most birds. Most birds must dart through 

 the air at a relatively high rate of speed in order to maintain themselves 

 aloft, and even the swallows, which like bats feed on flying insects, must 

 perform long sweeps through the air. The bat is able to fly fast or slowly, 

 to turn sharply, and to check its flight abruptly, if occasion demands. It 

 can thus control its passage through the air with greater precision. When 

 not in flight a bat clings, head downward, to some upright surface, using 

 for this purpose the slender, curved, and sharply pointed claws of the 

 hind feet. 



The wings of a bat are provided with numerous sensory hairs which 

 upon being struck by air waves apprize the animal of the location of 

 objects in its vicinity ; and this fine sense of touch, if such it may be called, 

 is the basis of the bat's ability to course about in twilight or even in pitch 

 darkness without striking objects as would a mammal or a bird which is 

 dependent solely upon sight. The ears of bats are proportionately large 

 (see pi. 21 and text figs. 7, 8), and these big external conchs probably catch 

 sound waves made by flying insects and thus the bat becomes aware of 

 the direction of objects of prey. 



Bats spend the day in some sort of retreat, the location chosen being 

 more or less different for each of the different species. But such retreat 

 is never dug or modified; nor is any bat known to make a nest as do so 

 many other nocturnal mammals. Some species such as the Free-tailed 

 and Pallid bats are characteristically colonial ; others, such as "the Little 

 California Bat, are usually, but not always, solitary ; while the Hoary Bat 

 seems to be strictly solitary. Each species issues forth when the light 

 of day has reached a certain degree of weakness — a different degree for 

 each species — and once abroad, each hunts its prey in a rather definite 

 niche. The pursuit of prey usually occupies only a short period at and 

 after dusk, though additional foraging may be done just before daybreak. 

 The daytime hours and, with most species, the middle of the night are 

 spent in rest. Bats are therefore abroad and active less than almost any 

 other sort of animal; this is likely made possible, in part at least, by the 

 concentrated nature of the food upon which they subsist. 



