Big Brown Bat (Eptesicus fuscus)

Protection Status Notes
E. fuscus is not listed by the U.S. Fish and Wildlife Service.
Eptesicus fuscus is a relatively large, robust bat with a broad, sparsely furred nose and keeled calcar. Its fur color varies from light copper to dark chocolate brown. It has a relatively blunt and rounded tragus. Its forearm is 42-52 mm long, and it bat weighs 12-30 g. It most closely resembles the much smaller evening bat, which never has a forearm longer than 39 mm. It differs from all myotis bats in having upper premolars that are at least half as long as the canines. Those of myotis bats are much shorter, often barely visible.
Life History
Though Big Brown Bats thrive in a variety of habitats, they appear to prefer deciduous forests. They are extremely hardy and often are the last bats to enter hibernation in late November and early December. They mate in fall before entering hibernation, though some mating has been recorded in spring. Females form maternity roosts where they give birth from May to July. Pups are born naked; their eyes and ears open a few hours after birth. They learn to fly within 18 to 35 days and are weaned about two weeks later. They accompany their mothers on early foraging flights, and may continue to do so for up to 17 days after learning to fly. During the maternity season, most males live alone or in small bachelor colonies. Once young become independent, nursery colonies break up, and there is greater mixing of sexes before travel to hibernation sites. Big Brown Bats have been known to live for up to 20 years in the wild.

Most Big Brown Bats hibernate in winter. Some exhibit life-long loyalty to their chosen over-wintering sites. These bats are also extremely loyal to the roosts where they are born and will return there year after year. In caves, they typically squeeze into tight crevices in especially cold areas near entrances. This helps protect them from sudden changes in air temperature, while additionally concealing them from predators. A large proportion of Big Brown Bats now live in buildings, some year-round.

In the summer, Big Brown Bats emerge just before or soon after sundown, though some individuals will emerge even in mid-day to drink or feed when they are especially stressed. Feeding activity is most intense within the first two hours after sunset, but may occur anytime during the night. Regardless of the day roost chosen, individuals typically select separate night roosts where they rest between meals. Big Brown Bats do not show a preference for feeding over water versus land, or for forests versus clearings. They often feed over wetlands, crops, parks, roadways, and around street lights. Big Brown Bats are able to identify and select prey by listening to low frequency sounds made by the wings of flying insects. Small beetles, such as ground beetles, scarab beetles, and spotted cucumber beetles, are their most frequent prey, though food choice can be highly variable among seasons and localities.
This bat has adapted to many habitats, from lowland deserts to timberline meadows. Though it originally lived in snags in old growth forests, it often lives in buildings.
The Big Brown Bat lives from Alaska and central Canada, south through the continental United States, Caribbean islands, Mexico, and Central America, the southern-most part of its range reaching northern South America.

Widely distributed over most of the eastern and western parts of Texas, but not yet recorded in the central part of the state or in Hawaii and southern-most Florida.
Threats and Reasons for Decline
The big brown bat is one of the most widespread and abundant bats in North America, yet little is known about its current status relative to past numbers. As fewer bats are permitted to live in buildings, even this ubiquitous species has declined in areas that have been closely monitored.

Loss of roosting snags forces big brown bats to use buildings, where they are often killed by people or pets. Although this species coexists well with humans, inappropriate nuisance control measures put the bats needlessly at risk, even though exclusion is a more effective long-term solution.
Ongoing Recovery
Big brown bats rank among America's most beneficial animals. Given their important roles in controlling garden, forest, and agricultural pests, they deserve protection whenever possible. When nuisance problems require exclusion from buildings, this species readily accepts properly built and located artificial roosts.
Little is known about the status of this species relative to past numbers, and its impact on forest pests remains unstudied. This U.S. bat species is most closely associated with people.
For more information

Additional details can be found in the online version of The Mammals of Texas for the Big Brown Bat