these are usually of considerably fewer individuals than 

 hibernating clusters. In Illinois, the gray bat and the 

 southeastern bat are the only species whose females re- 

 main in caves to bear their young; all other cave bat 

 species in Illinois establish maternity colonies in build- 

 ings, trees, or other structures. 



Little Brown Bat, Myotis lucifugus. This small bat has 

 an 8- to 10-inch wingspan and weighs about Vi ounce. 

 Its sleek, glossy fur ranges from pale tan to reddish or 

 dark brown. Easily confused with several other species 

 of myotine, or "mouse-eared" bats, the little brown bat 

 is very common throughout Illinois during the summer. 

 Females establish large maternity colonies in buildings 

 and give birth to one pup yearly. Males are solitary or 

 live in small bachelor colonies. Following hibernation, 

 this species is rarely found in caves; but without a 

 doubt, little brown bats far outnumber any other spe- 

 cies of hibernating bat in Illinois during winter, with 

 clusters sometimes numbering in the tens of thousands. 

 Accordingly, little brown bats have been one of 

 the most frequently studied species, and they are still a 

 favored subject. Long-term studies of the movements 

 of little brown bats from an abandoned mine in north- 

 central Illinois have given us much insight into the 

 natural history of this species. 



Gray Bat, Myotis grisescens. Typically weighing less 

 than '/3 ounce, this bat is usually uniformly gray in color 

 (some are russet). It is dependent on caves for roosting 

 habitat during both summer and winter. For this 

 reason, it has never been common in Illinois and has 

 been reported almost entirely from regions with natural 

 caves in the southern and west-central portions of the 

 state. A cave in southern Illinois that once housed 

 more than 10,000 gray bats has now been abandoned; 

 very few of the approximately 400 caves in Illinois pro- 

 vide suitable habitat for this endangered species, and 

 those that do have long since been abandoned because 

 of habitat destruction and human disturbance, for the 

 species is highly sensitive to disturbance. Their vul- 

 nerability is indicated by the fact that 95 percent of the 

 entire known gray bat population hibernates in just 

 eight caves in five states. 



Maternity colonies may contain thousands of 

 females, each bearing a single pup. These females form 

 tightly packed clusters in dome-shaped pockets in the 

 ceilings of caves. Female gray bats captured over the 

 Cache River in Johnson and Pulaski counties had given 

 birth that season and were nursing young, but their 

 maternity site could not be found. Efforts to capture 



Silver-haired bat eMeninTullle, rue National Auouu 



gray bats at caves they once occupied have resulted in 

 the taking of only a few males. Il 



