64 Order CHIROPTERA 



length of a foot and a wing span of 5 feet. The 12 species of 

 bats in Illinois, all belonging to the family Vespertilionidae, 

 are harmless and small, the largest being only 5i/2 inches from 

 nose to tip of tail and having a wing span of about 14 inches. 



The species of bats in Illinois can be divided into two general 

 groups. Individuals in one group tend to be solitary (live 

 alone) ; to roost in trees (hang from branches with their heads 

 down or hide under loose bark) ; and to be migratory (move 

 south, probably out of Illinois, late in the fall and north in the 

 spring). This group includes the red, the hoary, and the silver- 

 haired bats. 



Individuals in the second group tend to be gregarious (live 

 together in colonies) ; to hibernate in caves or abandoned mines 

 in winter and roost in buildings, caves, or hollow trees the re- 

 mainder of the year; and to be nonmigratory (except in one 

 species). 



Mating among Illinois bats typically occurs late in the fall, 

 ovulation and fertilization the following spring. The young are 

 born in late spring or early summer. At this time the sexes usu- 

 ally segregate; some colonies consist entirely of males and 

 others of females with young. The number of young produced 

 annually by a female is usually one or two; the number varies 

 with the species involved. The bare, much wrinkled, and blind 

 young have proportionately small hands, or wings, and modified 

 bladelike or forked and recurved milk teeth. These forked 

 teeth presumably aid the young in clinging tightly to the body of 

 the mother, inasmuch as she carries them until they are too 

 much of a burden or are old enough to fly. Sometimes the com- 

 bined weight of two young exceeds that of the mother. Develop- 

 ment is extremely rapid, some young being able to fly at the age 

 of 3 weeks. 



Signs. — Bats leave signs of their presence in the form of drop- 

 pings, or guano, and the remains of partially eaten insects. Be- 

 cause such signs are the same for most species of bats, a brief de- 

 scription of them is summarized here, rather than in the descrip- 

 tion for each species. Bats of the first group mentioned above, 

 sometimes referred to as the tree bats, seldom leave sufficiently 

 large accumulations of guano and insect remains to be easily rec- 

 ognized as bat signs. Bats of the second group leave deposits of 

 droppings and insect remains that may be several feet deep 

 under the roosting sites. Caves long inhabited by summer colo- 



