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Big Brown Bat

Glossy chestnut brown above, paler below. Wings, tail, ears and nose are dark brown to black. In hand, it can be distinguished by the large size, distinctly keeled calcar, and a large forearm that is more than 1.5 inches in length.
In winter months, this bat is most often found hibernating in large dry caves and mines with a relatively high amount of airflow. The presence of big brown bats in Oklahoma seems to be limited by the availability of these hibernating conditions. Though they may form small clusters, hibernating big brown bats are typically found singly, nestled in crevices with both their back and belly touching a rock surface. During the rest of the year, big brown bats roost in caves, tunnels, trees cavities, wood piles and bat boxes. Big brown bats are one of eight species of Oklahoma bats known to use bat boxes.
Life Cycle: 
Big brown bats use their large powerful jaws to eat flying beetles and moths. These bats are often seen foraging near light poles and other places large numbers of insects congregate. Pups develop between late May and late July. Like Oklahoma’s other hibernating bats, big brown bats mate in the fall. But fertilization doesn’t occur until the bats emerge in the spring. Females then form nursery groups and give birth to one to two pups in May.
Wingspan: 13-16 inches. Total Length: 3.5-5.25 inches.
How to Observe: 

Big brown bats take flight about 20 minutes after sunset. Their flight appears slow and deliberate. They may fly near the roost before flying off to feed. For more information about this and other bats, download the free "Bats of Oklahoma Field Guide."