Scientific Name: Eptesicus fuscus
• forearm — 1.65 to 2.01 inches (4.2 to 5.1 cm)
• wingspan — 12.80 to 13.78 inches (32.5 to 35.0 cm)
• ears — with rounded tragus
Distribution: The big brown bat is native to North America, Central America, the Caribbean, and extreme northern South America. The big brown bat is one of the most widely distributed of bats in the United States and is probably familiar to more people than any other species. This is partially due to its large, easy-to-observe size, but also to its ability to overwinter in buildings (attics, wall spaces, and basements).
Color: From reddish brown, copper colored, to a dark brown depending on geographic location. This is a large bat without distinctive markings. Confusion may occur with the evening bat (Nycticeius humeralis) though the latter is much smaller.
Habits: This hardy, rather sedentary species appears to favor buildings for roosting. Summer maternity colonies may include a dozen or so and up to a few hundred individuals, roosting behind chimneys, in enclosed eaves, in hollow walls, attics, barns, and behind shutters and unused sliding doors. They also form colonies in rock crevices, beneath bridges, in hollow trees, and under loose bark. Litter size is 2 in the East to the Great Plains; from the Rockies westward 1 young is born.
E. fuscus frequently shares roosts with M. lucifugus in the East, and with M. yumanensis, Taderida, and Antrozous in the West. Males typically roost in smaller groups or alone during the summer. Its close proximity to humans, coupled with its tendency to move about when temperature shifts occur, often brings this bat into human living quarters and basements in summer and winter. Big browns also hibernate in caves, mines, storm sewers, burial vaults, and other underground harborage. While E. fuscus will apparently travel as far as 150 miles (241 km) to hibernacula, the winter quarters of the bulk of this species are largely unknown. Big brown bats may live as long as 18 years.