The big brown bat feeds mainly on beetles (1) (2) (3) (6) (7), using its powerful jaws and strong teeth to bite through their hard wing cases (1) (6). Other prey items include flies, flying ants, lacewings, caddisflies and moths, as well as other flying insects (1) (3) (4) (8). The big brown bat is considered to be an important predator of insect pests such as the spotted cucumber beetle (Diabrotica undecimpunctata), scarab beetles, stinkbugs and leafhoppers (8).
Like most other bats, the big brown bat forages at night, usually leaving its roost within the second hour after sunset to feed (2) (6). This species will forage in a variety of habitats, both over water and over land, and uses forests and clearings as well as rural and urban areas (2) (6) (7). The big brown bat has been shown to be able to use the Earth’s magnetic field to help it find its way back to its daytime roosting site (9).
Like many other bats, the big brown bat also navigates and hunts using echolocation (2) (3). When leaving its roost, it may also listen for the sound of chorusing frogs and insects to help it locate concentrations of prey (10). In addition to producing ultrasonic calls for echolocation, the big brown bat uses a variety of ‘social’ calls to communicate with other individuals (11).
Over most of its range, the big brown bat hibernates during winter, usually alone or in a small group. This hardy bat is often one of the last species to be seen flying about in autumn, and some individuals do not begin to hibernate until November (2) (3) (4) (6). Individuals often become active for brief periods during the winter months, sometimes even changing hibernation site (1) (2) (3) (4), and big brown bats in Cuba may not hibernate at all, instead merely entering a state of torpor on cool winter nights (6).
Female big brown bats emerge from hibernation in spring, usually around March or April (3) (4), and form ‘maternity’ colonies in which to give birth and rear their young (1) (2) (3) (4). These colonies vary in size from around 5 to 700 individuals (1) (2) and may be located in buildings, hollow trees or caves (2) (3) (4) (6) (7). During this time, the male big brown bats roost alone or in small all-male groups, only rejoining the females later in the summer (1) (2) (3) (6).
The big brown bat mates during the autumn, or sometimes during the winter and early spring, but fertilisation does not occur until the spring. The female big brown bat usually gives birth to one or two young in May to July, after a gestation period of about two months (2) (3) (4) (6). The young bats are born naked and blind (2) (3), but their eyes open on about the second day (3). The female leaves the young in the colony while she feeds, and is able to recognise her own offspring when she returns, even retrieving them if they have fallen to the ground (2) (4).
Young big brown bats are able to fly at about three to five weeks old (2) (3) (6) and reach adult size after about two and a half months (3). The male big brown bat reaches sexual maturity in its first autumn, but only some females reproduce at the end of their first year (2) (3) (6). The big brown bat may potentially live for 19 or 20 years in the wild (1) (2) (3) (4) (6), but many die in their first winter (1). A common cause of mortality in the big brown bat is failure to store enough fat for hibernation (1), although this species is also occasionally taken by predators such as owls, cats and snakes (2) (4).