Big Brown Bat {Eptesicus fuscus) 



Description: This species is easily distinguished from other bats in the Northern Rocky 



Mountains by its large size (only the Hoary Bat is larger); weight range is 16-30 g. 

 Pelage is brown, with hair extending only slightly onto the wing and tail membranes. The 

 dark-colored ears are of medium size (12-19 mm); the tragus is less than half the length 

 of the ear and is blunt. Calcar is usually keeled. Tip of tail extends about 5 mm beyond 

 tip of uropatagium. 



Distribution: Widespread across all of the United States and southern half of Canada south to 

 northern South America. 



Habitat and Habits: Found in a variety of wooded and semi-open habitats. Colonial, often 



forming colonies in tree cavities, rock crevices and buildings. Hibemacula include caves 

 and mines, buildings (attics) and other man-made structures; winter records exist from 

 Alberta (Schowalter and Gunson 1979) and British Columbia (Nagorsen et al. 1993). 

 Maternity colonies have been found in attics, bams in northeastern Montana (Swenson 

 and Shanks 1979), and sometimes in tree cavities. Mating occurs in fall and winter. 

 Pregnant females have been collected in Carter County, Montana in late June; lactating 

 females have been collected in early July, and volant young have been collected in 

 mid- July and early August (Jones et al. 1973); most young in Alberta are bom in late 

 June (Schowalter and Gunson 1979). Emerges at twilight to hunt for an initial period of 

 about five hours, after which activity declines; often forages over meadows, around yard 

 lights, and along tree-lined streets. In 1994-1995 this species was detected on the 

 Kootenai National Forest at one site in July, 27 sites in August, and 30 sites in September 

 (Appendix 3). 



Status: Considered less common in Montana than elsewhere in the United States (Hoffinarm and 

 Pattie 1968); uncommon in Glacier National Park (Lechleitner 1967), but the most 

 common bat in Carter County, Montana (Jones et al. 1973). Present in the Idaho 

 panhandle (Groves and Marks 1985). This species was detected on all Districts of the 

 Kootenai National Forest in 1994 and 1995 (Appendix 4). The big brown bat is not listed 

 by any federal agency. 



Natural Heritage Program rank: G5; S4. 



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