The big brown bat (Latin name Eptesicus fuscus) is a relatively large (hence its name) species for a bat, with a wingspan of roughly one foot. Like other bats, it is nocturnal, flies and hunts by navigating with ultrasonic bursts, and survives on a diet of insects; like its fellow north-inhabiting cousin, the little brown bat, it also hibernates during the winter. They typically live for twenty years, during which they spend summers hunting and eating, fall migrating and mating, and winter hibernating.
– Birth and Maternity Colonies –
Baby big brown bats are invariably born in the spring months, typically either May or June according to the National Park Service. Although their mother bears them as live young after the hibernation period is over, she may have carried them in her body over the entire winter at that point. Births occur in the hibernation areas, of relative warmth and humidity to protect the bats from the bitter cold outside. Natural hibernation areas include hollowed-out trees and caves; as humans have invaded the bat’s territory across North America, this has also spread to include the attics of houses.
While male bats typically depart from the hibernating location and migrate back to their summer habitats after awaking, babies remain, accompanied by their mothers, for roughly a month, during which they live off of her milk and slowly learn to fly within the relatively safe environment of the cave (or other site). After this, they may spend several more weeks in close proximity to their mother as they learn to catch their own food. Once they have learned to do so, however, the young big brown bats are essentially on their own. During this period, the groups of female bats and their offspring are referred to as “maternity colonies.”
– Adult Life –
After leaving the maternity colony, young big brown bats effectively must settle into the annual life cycle of all other big brown bats. This means a nocturnal pattern of sleeping by day in roosts similar to the hibernation area, except less suited for winter habitation, followed by several hours of night-time hunting using their unique capacity of echolocation (locating prey and other animals by emitting and detecting high-pitched cheeps, comparable to the human submarine technology of sonar).
Either by their first fall or their second, these young bats will have reached full adulthood, capable of mating and, in the case of the females, bearing young of their own. Typically, a female will return to and bear her young in the same maternity colony in which she was born herself, although of course this is far from always the case.
In theory, bats may continue this cycle for up to 20 years in the wild. Obviously, however, the average big brown bat’s lifespan is considerably shorter, usually as a result of the bat falling prey to various predators. A large number of big brown bats will die within their first season on their own.