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Photo by: J. Scott Altenbach
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Eptesicus fuscus (Beauvois, 1796)

Big Brown Bat

Federal Protection: No US federal protection

State Protection: No Georgia state protection

Global Rank: G5

State Rank: S5

SWAP High Priority Species (SGCN): No

Element Occurrences (EOs) in Georgia: 0

Habitat Summary for element in Georgia: Georgia habitat information not available


Big brown bats have brown glossy fur on their back with the belly fur being lighter and paler. Their ears are small, rounded and black in color as are their wing membranes and tail. Their lips are fleshy and their nose is broad. Their average weight is 0.5-1.2 oz (14-21 g). Their wingspan is 12-16 inches (32-40 cm). Relatively large for a North American bat, this species measures 10.3-13 cm (4.1-5.1 in) in total length.

Similar Species

Big brown bats look most similar to evening bats, mostly distinguished from them by their larger size and forearm length. They are somewhat similar to Myotis species except that they are much larger in body size and have a swollen appearance around the muzzle. Big brown bats also have noticeable differences in ear and ankle anatomy.


Big brown bats inhabit many different environments including hollow trees, under loose tree bark, caves, and crevices in rock ledges. Human activities have provided more potential roosts in the form of old mine shafts, buildings, and homes.


The big brown bat feeds on beetles, flies, moths, and true bugs which it catches and eats while in flight. It forages for food by flying slow, straight courses over water, forest canopies, wooded clearings, and around city lights.

Life History

Big brown bats mate in October, before winter hibernation, and after a delayed fertilization over winter and a 60 day gestation, give birth to one or two pups in late May or early June. These bats are typically solitary creatures, except when in nursing colonies and at winter roosts. The average number of females in a maternity colony can range from 40-100 bats. Pups are normally fully weaned after 5 weeks. Big brown bats can live up to 19 years in the wild.

Survey Recommendations

Ultrasonic detectors can be used to survey big brown bats. Acoustic surveys can determine presence/absence, phenology, and distribution. There are three seasons for acoustic surveys: spring (April and May), summer (June and July), and fall (August and September).


They range from the extreme northern parts of Canada through the United States, Mexico, Central America, northern South America and the Caribbean Islands. The Big Brown Bat is a year-round resident in Georgia that hibernates in the winter months either by itself or in groups of up to 100 individuals in well-protected roosts such as caves, mines, or buildings. In Georgia this bat is common statewide.These bats are widespread partly because they can withstand a variety of habitat conditions.


There are many threats to North American bat species including habitat degradation, hibernaculum disturbance, pesticide use, wind turbines, and white-nose syndrome. Since its discovery in North America in 2007, white-nose syndrome (WNS) has caused a huge decline of bats. The fungus grows on the bodies of hibernating bats and wakes them up from hibernation, causing a loss of important metabolic resources for surviving during the winter months. Mortality rates of bats at some hibernation sites have been as high as 90%. Fortunately, most big brown bats in Georgia do not spend their winters in caves and have not been negatively affected by  WNS in our state.

Georgia Conservation Status

Big brown bats are considered common and are currently not of special conservation concern.

Conservation Management Recommendations

Big brown bats can be very beneficial by consuming agricultural pests and in some areas farmers are encouraging bats to form maternity colonies in bat houses. Another suggestion is to design bridges specifically for the use of roosting (Whitaker 1995). Disturbance to hibernating bats should be avoided. Forest management activities at summer roost sites should ensure that forested foraging habitat is available and that no known roost trees are destroyed.  Preventing the spread of WNS is also critical for the future survival of bats.


“Big Brown Bat.” National Parks Service, U.S. Department of the Interior, www.nps.gov/shen/learn/nature/big-brown-bat.htm.

“Big Brown Bat ( Eptesicus Fuscus).” University of Georgia: Museum of Natural History, fishesofgeorgia.uga.edu/gawildlife/index.php?page=speciespages/species_page&key=efuscus.

Barbour, R.W. and W. H. Davis. 1969. Bats of America. Lexington: The University Press of Kentucky.

Mulheisen, Michael, and Kathleen Berry. “Eptesicus Fuscus (Big Brown Bat).” Animal Diversity Web, animaldiversity.org/accounts/Eptesicus_fuscus/.

Whitaker, J. Oct. 1995. Food of the Big Brown Bat Eptesicus-Fucus From Maternity Colonies in Indiana and Illinois. American Midland Naturalist, 134:(2): 346-360. 

Whitaker, J., S. Gummer. May 1992. Hibernation of the Big Brown Bat, Eptesicus-Fuscus, in Buildings. Journal of Mammalogy, 73:(2): 312-316.

Authors of Account

Sarah Krueger

Date Compiled or Updated

S. Krueger, March 2020