A moth attempts an evasive movement 

 as an echolocating greater horseshoe bat 

 approaches. The bone development of 

 these bats, which are native to Europe, 

 Asia, and North Africa, is adapted for 

 maneuverability in flight. 



Stephen Dalton; NHPA 



allowing them to ingest an adult diet al- 

 most as soon as they begin flying. By con- 

 trast, young mice must eat a soft diet for 

 some time until their adult teeth come in. 



As the juveniles begin to be weaned, 

 both their teeth and wings develop enough 

 to allow attempts at hunting insects in 

 flight. About a week after they begin fly- 

 ing, they shift to the adult diet of moths, 

 flies, and beetles. Now their teeth are ca- 

 pable of masticating food, but young bats' 

 abihty to capture prey remains limited by 

 underdeveloped wings and inexperience. 



During the three weeks after birth and 

 just before its first flight, a juvenile bat's 

 wings develop faster than they did in the 

 prepartum period. At the time of their first 

 flight, the wingspan of a little brown bat 

 may be only 20 percent of an average 

 adult's. 



Because they receive elaborate parental 

 care in the maternal roost, most newborn 

 bats survive the first few weeks of life. 

 After juveniles begin to take flight, how- 

 ever, the mortahty rate soars, and most do 

 not make it through the first year. Because 

 a growing bat's wings change somewhat 

 in size and shape practically every fime it 

 attempts to fly, there are subtle but notice- 

 able changes in wing performance. 



If someone were confinuaUy changing 

 your car's power and cornering ability 

 while you were learning to drive, you can 

 imagine how difficult it would be to avoid 

 disaster. An analogous situation exists for 

 young, newly flying bats. 



Among insectivorous species, the 

 young must quickly become capable of 

 capturing enough insects to fuel a heart 

 rate that exceeds 1, 100 beats per minute in 

 flight. When grounded because of exhaus- 

 tion or poor flight skills, the young are 

 soon gobbled up by raccoons, skunks, 

 snakes, or coyotes. But even though "de- 

 velopment on the wing" is a highly precar^ 

 ious adventure, more than nine hundred 

 different species of bats have evolved 

 throughout the world — about 25 percent 

 of all living mammalian species. With all 

 its perils and improbabilities, "batness" 

 has been a tremendously successful en- 

 deavor for these mammals. D 



54 Natural History 1/94 



