Big Brown Bat

Big Brown Bat​ (Eptesicus fuscus)

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One of Kentucky’s largest bats, the big brown, sometimes attains a length of nearly 5 inches and can have a wingspan of over 13 inches. These bats are glossy brown, slightly lighter underneath. Key features include a large, hairless muzzle, a blunt-tipped tragus, and a keeled calcar.

Behavior

Big brown bats are associated primarily with man-made structures, as they have adapted well to the changes humans have brought to the landscape. Consequently, they are the bats most often encountered by humans. All known Kentucky maternity sites have been found in buildings of some type or under bridges. These hardy bats also roost in the eaves of buildings during winter unless the temperatures become too extreme. The species forages in many open and semi-open habitats, often around streetlights. 

These bats have relatively large teeth, which aid them in consuming their preferred prey, beetles. They have been called a ‘friend of farmers’ because they eat several agricultural pests, such as the cucumber beetle, whose larvae can significantly affect corn production. 

Maternity colonies consist of a few to more than one hundred females. Each female generally gives birth to twins in early June. Males are primarily solitary. Big brown bats hibernate in caves in winter, usually in the coldest sections near the entrance. They typically roost singly or in small groups of less than a half-dozen individuals, often in rock crevices.

Habitat Information

Big brown bats' habitat range occurs throughout most of North America, from central Canada, south through Central America into northern South America.

Figure 1: Map showing where Big Brown Bats have been reported by county. Counties colored in teal have confirmed reported sightings. Updated -  Feb. 2017​

The species is a year-round resident of Kentucky and does not likely move great distances between winter and summer roost sites. Big brown bats occur statewide, although they appear absent from the Mississippi Alluvial Plain in the far western part of the state.

A big brown bat, showing its teeth, used to eat beetles

Big brown bats under the bridge in the gap between the concrete beams.​ (Photos: John MacGregor)