Little Brown Bat, Myotis lucifugus

The little brown bat (Myotis lucifugus) is also known as the little brown myotis. It is a species in the Myotis genus, or mouse-eared bats. It is one of the most common North American bats, and is a good species to use when studying bats. This species has been included in the Mammalian Genome Project. The range of this bat includes the northern half of the United States and southern Canada. More males than females have been found in the northern range of the little brown bat, but there has been one nursery group found in the Yukon. Probably due to unintentional transportation by ship, some little brown bats have been found in Iceland and Kamchatka.

The little brown bat will stay in three roosting areas. These include night and day roosts, and hibernation roosts. The hibernation roosts are used only in winter, and the night and day roosts are used through the rest of the year. Little brown bats will roost in a number of different places, including manmade structures. Nursery roosts have been found in structures as well, but can also be in hollow trees. Night and day roosts are typically in the same place, although different areas of the home will be used for different times. During the nighttime, bats will roost closer together for warmth. The usual hibernating roost will occur in a cave, although brown bats have been known to roost in abandoned mines.

The fur of the little brown bat matches its name, as it is mostly dark brown fur that covers its body. The underside of the brown bat is usually a lighter grey in color. The ears are small and black, and the wings are usually brown. The wingspan of the little brown bat is between 8.6 inches and 10.6 inches, and they have an average weight between 0.2 and 0.5 ounces. They can be up to 3.9 inches in body length, with females usually being larger than males.

The little brown bat does not have a sagittal crest, which is typical among mammalian and reptilian skulls, and the nose is short. All thirty-eight teeth are relatively sharp, giving this bat, like most insectivores, easy ability to eat their food. This bat is discernible from the Indiana bat due to the lack of fur on its tail, and the long hair on the feet that extend past the toes. Another distinct feature of the little brown bat is its shorter legs. It also has less hair on the front of its wings.

Behaviors of the little brown bat are typical to most bat species. They are mostly nocturnal, leaving the roost around dusk and are most active a few hours after that time. The can also be active in the early morning hours.  In captivity, these bats will sleep approximately 19.9 hours a day. This allows the bats to conserve energy for hunting insects.

The diet of the little brown bat consists of beetles, gnats, wasps, moths, mayflies, midges, and mosquitoes. Many of the insects they feed on have an aquatic life stage, so these bats will roost near water in order to have a good food supply. Foraging is done in groups that move in and out of nearby vegetation. They will forage over water for their food. As with other bats, the little brown bat will glean their food, a process by which they pick food off a surface, and they will also catch food in midair. In the air, little brown bats will scoop insects with their wings, while over water insects are eaten directly with the mouth.  Echolocation is used to gather food, and is best used when flying packed together in a group. Brown bats will not claim territories for food, but they will return to previous areas where they have foraged. They will usually hunt no more than two species of insect per feeding, unless the group has been scattered. If foraging was unsuccessful, these bats will enter a state of torpor, similar to hibernation, until the next nights feeding.

Little brown bats will use high intensity frequency modulated calls, emitted in short bursts between less than one millisecond and five milliseconds. The sweep rate of this echolocation is 80–40 kHz, focusing most of their energy at a rate of 45 kHz. While foraging, brown bats will emit two hundred calls per second, while in normal flight that number is reduced to twenty calls per second. In order to land, the bat will emit a high-pulsed repeated call. If a bat is in danger of crashing into something, it will emit a call similar to honk at 25 kHz.

The little brown bat will migrate, and similar to other bats, the migrating path differs for males and females. During the summer, they will live apart while the females raise young. During the colder months, brown bats will migrate together, mate, and then hibernate for a prolonged period due to a lack in food sources.

The mating habits of the little brown bat are somewhat odd. Two types of mating can occur. During passive mating, male bats will try to mate with any sleeping bat they can, whether it is male or female. During active mating, both bats are awake. Passive mating occurs until winter, while active mating peaks in August. These bats do not mate for life, and males will mate with many females throughout the season if possible. If a female struggles, males may emit a soothing call to calm her down. It is not known if female little brown bats store sperm, as is common in other bat species.

In spring, female brown bats will fly to “nursery colonies”, and these may be where they were born. The populations of these colonies consist mostly of females and young. Many bats will choose warm attics to roost within. Colonies in the wild located in caves or forests can reach a number of one thousand bats. Born in late May to early July, there is typically one pup born per female per year. Sometimes twins can occur. Little brown bat pups are born helpless and blind, and will roost while their mother’s forage for food. Their eyes will open on their second day. Pups will spend their time latched onto their mother’s nipple, and at three weeks will learn to fly. At nearly one month old, the pups are ready for adulthood and most will mate by their first autumn.

The little brown bat can live more than ten years, but its average lifespan in six to seven years. Predators of this bat include snakes, birds, rats, and small carnivores. Most bats are not killed by parasites or predators, but are killed by accidents occurring like running into barbed wire.  They can also drown in floods while hibernating.  Pesticides sometimes kill these bats, although DDT does not typically affect them. Rabies is not common in this species of bat. Although the little brown bat is listed as a species of least concern, due to a disease known as white-nose syndrome, many areas in eastern North America are listing little brown bats as a protected or sensitive species.