Big Brown Bat Eptesicus fuscus

E. fuscus has a head and body length of 35-75 mm, tail length is 34-60 mm, and forearm lengths of about 28-55 mm. Adult weights are about 14-30 grams. Coloration ranges from dark brown to black above and paler below. A buffy wash is sometimes present.

In North America, E. fuscus is found in forest where hollow trees are used for roosting in the summer and for hibernating during the winter. This species is, however, the one most adapted to humans and will also use attics and church belfries for roosting. Any moist dark cavernous structure can be inhabited by E. fuscus, including houses, tunnels and storm sewers. They have no real migration and generally live in one area their entire lives. Hibernation periods are fairly short, recorded from December to April in Canada.

They emerge at sunset, having a slow, ponderous flight and feed closer to the ground than bats with a more quick and erratic flight. Their main diet consists of insects, making them beneficial to humans.

Maternity colonies are formed by females and their young. During this time the males roost alone or in small groups. Later in the summer, both sexes are found roosting together. Hibernating colonies generally have more males than females. Within its range, E. fuscus usually has one young in the Rocky Mountains and west of that line and twins to the east of that line.

E. fuscus is found in S Canada to Columbia and N Brazil; Greater Antilles; Bahamas; Dominica and Barbados (Lesser Antilles; and Alaska.