Big Brown Bat

Photo of the Big Brown Bat/Murci��lago Marr��n Mayor

Big Brown Bat (Eng.), Murciélago Marrón Mayor (Sp.),Eptesicus fuscus(Sci.), ranges from southern Canada, through temperate North America, down through Central America to extreme northern South America and the West Indies islands.

Photo: Information compiled by Alan Mowbray, Interpretive Media Writer, EYNF/LEF

General Information

Taxonomy: ClassMammalia; OrderChiroptera; FamilyVespertilionidae; GenusEptesicus; SpeciesE. fuscus. First described by French biologist Palisot de Beauvois in 1796 in “Les environs de Philadelphia (Pennsylvania).


The Big Brown Bat measures 4.3 to 5.1 inches (110 to 130 millimeters) in total length – its tail makes up approximately 1.9 inches (50 millimeters) of its total length. Wingspan is approximately 13 inches (330 millimeters). Females are slightly larger than males (sexually dimorphism). It weighs between 0.3 and 0.8 ounces (11 and 23 grams). It has 32 sharp, heavy teeth, a broad nose and fleshy lips. Its eyes are large and bright and ears are rounded.

Upper body color ranges from pinkish-tan to dark brown. While the lower body fur is lighter ranging from pinkish to olive-buff. Naked parts (face, ears, wings and tail) are black.


E. fuscus females give birth in the spring 60 days after becoming pregnant, giving birth to one or two babies (pups). Average weight of a newborn pup is 0.1 ounces (3.3 grams). The babies are born blind with no fur but they grow quickly and are able to fly in two months. Females must eat at least their body weight in insects each night when they are nursing. Males do not participate in parenting activities.

They use echolocation to avoid obstacles while foraging for flying insects – they can track insects into vegetation and intercept them while avoiding obstacles. E. fuscus is an insectivore, primarily preying on beetles, using its powerful jaws and teeth to chew through the beetle’s hard exoskeleton. It also eats flying insects such as moths, flies, wasps and dragonflies.


Big brown bats are forest dwelling nocturnal animals, roosting during the day in hollow trees, beneath loose tree bark, in the crevices of rocks or in man-made structures such as attics, barns, old buildings, eaves and window shutters.


The Big Brown Bat is classified as a Species of Least Concern by the International Union for the Conservation of Nature (IUCN).

Where to look for this animal in the EYNF

These animals are uncommon, but they can occasionally be viewed near forest nature trails as they leave their roosting places to forage for insects at twilight.