The Big brown bat is a relatively large microbat distributed widely throughout North America, the Caribbean, and the northern portion of South America. Its dorsal fur is reddish-brown and glossy in appearance; its ventral fur is a lighter brown. Its snout, uropatagium (flight membrane between the hind limbs), and wing membranes are black and hairless. Its ears are also black in color; they are relatively short with rounded tips. The tragi (cartilage flaps in front of the ear canal) also have rounded tips.
Big brown bats are found from southern Canada and Alaska to as far south as Colombia and Venezuela. They have also been documented in the Caribbean in both the Greater and Lesser Antilles, including Cuba, Hispaniola, Dominica, Barbados, and the Bahamas. These bats are adaptable to many habitats; they live in urban, suburban, or rural environments and can also be found in forested regions.
Big brown bats are nocturnal, roosting in sheltered places during the day. They will use a wide variety of structures for roosts, including mines, caves, tunnels, buildings, bat boxes, tree cavities, storm drains, woodpiles, and rock crevices. They generally roost in cavities, though they can sometimes be found even under exfoliating bark. Both solitary males and solitary females may be found roosting under the bark. In the summer, males are most often solitary, though they may form small, all-male colonies. Males will also sometimes roost with adult females. Big brown bats often use echolocation to navigate. This means that they emit a call out into their environment and listen to the echoes of those calls that return from various objects near them. Using echolocation, Big brown bats can determine how far away an object is, the object's size, shape, and density, and the direction (if any) that an object is moving. Around November, Big brown bats enter into hibernation, often in a location less than 80 km (50 mi) away from their summer roosts. They often hibernate by themselves, or in small groups and come out of hibernation in the spring.
Big brown bats breed in autumn shortly before their annual hibernation. After hibernation ends in the spring, pregnant females separate into maternity colonies around April. Maternity colonies range in size from 5 to 700 individuals, though in the eastern US and Canada, they are frequently 25-75 adults. In the eastern United States, twins are commonly born sometime between May and July; in western North America, females give birth to only one pup each year. At birth, pups are blind, helpless, and weigh only 3 g (0.11 oz), though they grow quickly, gaining up to 0.5 g (0.018 oz) per day. The pup nurses from its mother for approximately one month. During this period mothers leave their pups at the roost while they forage at night. Pups begin flying at 3 to 5 weeks of age and become independent a few weeks later.
The Big brown bat is not considered at risk for extinction and doesn't face major threats at present.
According to IUCN, the Big brown bat is widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are increasing.
Big brown bats play a very important role in their ecosystem. They are significant predators of agricultural pests which makes them quite beneficial to farmers. A 1995 study found that, per year, a colony of 150 Big brown bats in Indiana or Illinois consumes 600,000 cucumber beetles, 194,000 scarab beetles, 158,000 leafhoppers, and 335,000 shield bugs - all of which cause serious agricultural damage.