Big Brown Bat

Eptesicus fuscus


• Mating: Polygamous

• Peak Breeding Activity: August through October

• Gestation Period: Approximately 2 months

• Young are Born: May and June

• Number of Litters per Year: 1. Young are called pups and are dependent on their mothers.

• Migration Patterns: Year-round resident. Big brown bats appear to home in on site-specific locations to live. Little is known about the dispersal of young.

• Feeding Periods: One hour or two after sunset and before sunrise

• Typical Foods: Insects, especially agricultural pests, including June and cucumber beetles, moths, and stinkbugs

• Facts and Falsehoods About Bats:

– Most bats do not carry rabies.

– Attacks by bats are extremely rare, even when the animals are provoked.

– Bats are not blind, nor are they interested in anyone’s hair.


As with the little brown bat, the big brown bat’s name is highly descriptive. Its fur is uniformly medium to dark brown on the upper parts, with slightly paler under parts. The fur is relatively long and silky in appearance, compared to other Ohio bats. The ears and wing membranes are dark brown.

Habitat and Habits

During the warm months of the year, big brown bats feed over a variety of habitats, including water, fields, forest openings, and urban and suburban areas. They use two primary types of habitats: hibernation sites used during the winter (e.g., caves, mines) and roosting sites for reproduction (e.g., buildings and under bridges) during the summer.

Reproduction and Care of the Young

Breeding takes place during the late summer and early fall during a behavioral phenomenon known as “swarming.” At this time, large numbers of bats visit and congregate in a succession of caves just prior to hibernation. Although sperm is transferred to the female during copulation that occurs in the fall, ovulation and fertilization of the egg are delayed until the females arouse from hibernation the following spring. During the summer, females form maternity colonies, mostly in man-made structures, especially barns. At this time, big brown bats avoid some of the higher roost temperatures tolerated by little brown bats, and will abandon any area that gets over 95º F.