big brown bat

LC - Least Concern

N5 - Secure

S3 - Vulnerable

Special Concern

Species in Greatest Conservation Need

Big brown bat is one of several bat species susceptible to white nose syndrome (WNS). WNS causes high mortality in cave and mine dwelling bats. Big brown bats hibernate in caves but also in human dwellings and other constructions, and may be less vulnerable to the disease.

Big brown bat is a common, large, vesper bat. It occurs from southern Canada to the northernmost countries of South America, and in the Caribbean. There are twelve subspecies currently recognized. Four subspecies occur in North America north of Mexico, only one occurs in Minnesota. It is the most common bat in Minnesota. It is found in wooded areas near water sources in hollow trees, in trees with cavities, crevices, and loose bark; and in buildings, bridges, and other human constructions. In winter it hibernates in caves, tunnels, and buildings.

Big brown bat is the second largest bat in Minnesota. Adults of our subspecies (E. f. fuscus) are 4¼″ to 5″ (110 to 130 mm) in length, have a 12¾″ to 13¾″ (32.5 to 35 cm) wingspan, and weigh ½ to 1 ounce (15 to 26 g). Females are slightly larger than males. Like most bats, they have two mammae.

The fur (pelage) is long, glossy, lax, and uniformly dark brown on the upper side, paler on the underside. The membranes on the wings, tail, snout, and ears are blackish-brown. The color and large size is enough to distinguish big brown bat from all other bat species in Minnesota.

The head is large, the nose is broad, the eyes are large, and the lips are fleshy. The ears are short, thick, erect, rounded at the tip, separated, inclined outward, and furred at the base. The fleshy projection at the base of each ear (tragus) is broad and blunt.

The wings are short and broad. The forearm length, a measurement significant to chiropterists (bat biologists), and included in all technical descriptions of bats, is 1¾″ to 2″ (46 to 51 mm).

The tail is 1½″ to 1⅞″ (38 to 47 mm) long and the tip projects slightly beyond the membrane between the thighs (uropatagium).

Total length: 4¼″ to 5″ (110 to 130 mm)

Wingspan: 12¾″ to 13¾″ (32.5 to 35 cm)

Tail: 1½″ to 1⅞″ (38 to 47 mm)

Forearm length: 1¾″ to 2″ (46 to 51 mm)

Weight: ½ to 1 oz (15 to 26 g)

Wooded areas; hollow trees; trees with cavities, crevices, and loose bark; buildings, bridges, and other human constructions; caves and tunnels

19 years

Bats are important vectors of the rabies virus but rabid bats pose little threat to humans. They are passive, will not attack, and will not bite unless handled.

Insects, especially beetles

Sources

4, 6, 24, 29, 30, 76.

Common

Bats on the picnic shelter wall in Monson Lake State Park.

Location: Milaca, MN

Released, unharmed, from the Cheese Ball Bin after a 1 minute video for identification.

Location: Monson Lake State Park

Bats on the picnic shelter wall in Monson Lake State Park.