Eptesicus fuscus (Beauvois, 1796), Philadelphia, Pennsylvania, United States. Ten subspecies.
OTHER COMMON NAMES
French: Chauve-souris brune; German: Große braune Fledermaus; Spanish: Murcielago ali-oscuro.
Body length ranges 3.5-5.3 in (9-13.5 cm), and forearm length about 1.6-2.2 in (4-5.5 cm). Adults weigh from 0.39 to 0.88 oz (11-25 g), with the heavier weights typical just before hibernation and the lighter weights immediately afterward. The dental formula of the big brown bat is (I2/3 C1/1 P1/2 M3/3) X 2 = 32. A small- to medium-sized bat with brown to reddish brown or tan dorsal pelage, a lighter-colored underside, and brownish black wings.
Throughout the continental United States, southern Canada, most of Mexico, the Caribbean, much of Central America, and northwest South America.
SIGNIFICANCE TO HUMANS
Big brown bats consume large quantities of pest insects. ♦
Big brown bats spend much of their summer in the hollows of trees, and small hiding places beneath tree bark or leaves. They are also common in attics, barns, and in other human-built structures. They are typically found near water and/or woods or meadows, but also are quite common in desert habitats. During the winter, they usually hibernate in caves.
Females will form maternity colonies, with three dozen or more females roosting together in an attic, tree hollow or other location. In the fall, big brown bats move to caves, where they soon enter hibernation. A hibernaculum may include only a handful of bats.
Their courtship and mating behaviors are unknown, although genetic differences between litter mates show that they may have different fathers.
Their diet includes scarab beetles, as well other flying and ground-dwelling insects. Big brown bats typically hunt on the wing, picking moths and other flying insects out of the air or snatching grasshoppers and beetles from the floor of an open forest. Each night, a big brown bat can eat several thousand insects, often equal to its body weight.
Mating commonly occurs in early spring, although some mate the previous fall or winter. Early mating females delay fertilization until the spring. Gestation lasts 50 to 60 days, and the young are born in late spring or early summer. Litter size is typically one or two altricial young per female. The young are weaned and begin to fly at about one to one-and-a-half months. Young females attain sexual maturity at four months, while males mature at four to 16 months. May be polygynous.
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