Big Brown Bat

## Description

The big brown bat (Eptesicus fuscus ) is a species of vesper bat distributed widely throughout North America, the Caribbean, and the northern portion of South America. It was first described as a species in 1796. Compared to other microbats, the big brown bat is relatively large, weighing 15–26 g (0.53–0.92 oz) and possessing a wingspan of 32.5–35 cm (12.8–13.8 in).

Big brown bats are insectivorous, consuming a diverse array of insects, particularly night-flying insects, but especially beetles. Some of the beetles it consumes are serious agricultural pests, including cucumber beetles. They are nocturnal, foraging for prey at night and roosting in sheltered areas during the day such as caves, tunnels, tree cavities, and human structures. Their breeding season is in the fall, shortly before their annual hibernation. After hibernation ends in the spring, females form maternity colonies for giving birth to young. Oftentimes only one offspring is produced per litter, though twins are common in the Eastern US. Lifespans of 6.5 years are considered average.

The big brown bat occurs widely throughout the US, Canada, Central America, and the Caribbean. Its range extends into parts of South America, found as far south as Colombia and Venezuela. It is adaptable to many habitats and is considered a generalist species. The big brown bat is not considered at risk for extinction, and is evaluated as the lowest conservation priority by the International Union for Conservation of Nature (IUCN).

While some other bat species in its range have experienced dramatic population declines due to the fungal disease white-nose syndrome, the big brown bat is relatively resistant to the effects of the disease, and some populations have even increased since the syndrome arrived in North America. Like all bats in the US, the big brown bat can be impacted by rabies, though some individuals have immunity against the virus. Even though sick bats are more likely to be submitted for testing, in 2011, only 3.8% of submitted big brown bats were positive for the rabies virus. Bat boxes are sometimes used to attract them as they are an agriculturally valuable species.

## Appearance

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.

## Distribution

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.

## Behavior

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.

## Diet

Big brown bats are carnivores (insectivores). They eat many kinds of insects including beetles, flies, stoneflies, mayflies, true bugs, net-winged insects, scorpionflies, caddisflies, and cockroaches.

## Reproduction

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.

## Population

### Population threats

The Big brown bat is not considered at risk for extinction and doesn't face major threats at present.

### Population number

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.

### Ecological niche

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.

## Fun Facts for Kids

The Big brown bat has been called "the most widespread Pleistocene bat in North America", as it is more represented in the fossil record of that time than any other bat species. Its extensive fossil record is known from more than thirty sites, including fourteen US states, Puerto Rico, Mexico, and the Bahamas.

In general, male Big brown bats live longer than females.

Female Big brown bats exhibit philopatry ("love of place"). Around 10-30% of female offspring usually return to their natal roost the following year and up to 72% of adult females use the same roost in subsequent years.

The use of echolocation allows Big brown bats to occupy a niche where there are often many insects (that come out at night since there are fewer predators then), less competition for food, and fewer predators.

Big brown bats tolerate cold weather fairly well, although they can be negatively affected by major changes in temperature. It is fairly common for some hibernating Big brown bats to awaken temporarily and seek warmer shelter, locate water, and even mate.

Big brown bats use bat houses for their roosts. Some landowners purchase or construct bat houses and install them, hoping to attract Big brown bats, largely due to their being an "agriculturally valuable species".