Big Brown Bats

Big brown bats (Eptesicus fuscus) is found all the way from southern Canada, across North America into Central America and all the way to the northern portion of South America. They are also found in the West Indies. This bat species is commonly found in rural areas, towns and cities although they can be found rarely in areas with heavy forest.

Big brown bats are from 110 to 130 mm with the tail making up from 38 to 50 mm of this length projecting just past the uropataguim. The front limbs are 41 to 50 mm with the rear foot being ten to 14 mm. The ears are 16 to 20 mm from the notch. There is a 13 inch wingspan on the big brown bat. The female of the big brown bat species is larger than that of the male. There are 32 teeth in the rather large skull of the big brown bat. The teeth can cause severe bits because of being heavy and sharp. This species has fleshy lips and a broad nose in addition to large, bright eyes. There is a rounded tip on the broad tragus, and the ears have a rounded appearance. This hat has an extension in a keel shape, and a cartilaginous calcar that articulates with the calacaneum.

The subspecies as well as the location will make the coloration of the pelage vary. The coloring ranges from rich chocolates to pinkish tans dorsally. An almost pinkish to olive color is on the lighter ventral fur. Black coloration is given to the areas without fur; the ears, wings and face. There have been a few of the species that have white spots on the wings as well as albinos of the species seen.

The big brown bat will mate just prior to hibernating although the spring is when the female of the species becomes pregnant. There is a sixty day gestation period after which one to two pups are born. The pup averages 3.3 grams in weight; they are don’t have fur and are blind at birth. The new born big brown bats grow fast and can fly by the first of July. It only takes seven days for the eyes to open, they are weaned by the time they begin flying, the parenting is done strictly by the female. This species of bat can also swim very well although they can’t take off from the waters surface.

Nursing females of the big brown bat species have to eat a minimum of half their weight in insects each night. The young are left alone in the nest while the female forages for food. Females will live in maternity colonies to raise the young. The colonies can contain anywhere from five to 700 little brown bats. The males will roost either in small groups or alone during this period, nesting of males and females together occurs in the late part of the summer.

Mothers of the big brown bat species can tell their young apart from others. The pups that get separated from the mothers will let out a squeak that can be heard over 30 feet away. This can enable the mother to find the young and return them to safety. Mothers lick the young on the face and lips before nursing when they find them. At four weeks old the young are able to forage for themselves and be the size of the adult bats by two months old.

Hibernation is done in both natural and man made environments by the big brown bat. Cool temperatures are preferred and allow them to tolerate conditions that other species of bats can not. This species may even be active during the hibernation period which enables them to move to a more desirable habitat. It is not known exactly what leads this species to hibernate however it has been found that as many as 340 days can be spent hibernating by this bat species.

The big brown bat is an insectivorous meaning that insects such as beetles make up the majority of its diet. They will eat a variety of flying insects such as the flying ant, dragonflies, flies, moths and lacewing flies. The big brown bat feeds in the warmer months when the insects are active meaning it has to have enough fat stored to enter hibernation when they are not. They will catch their prey as it flies. They require at least a third of the body weight to be a fat reserve to survive.

They will not feed when it is too cold or is raining heavily. The big brown bat normally starts to forage approximately twenty minutes after the sun sets. This species eats until it is full and then returns to the night roost to digest their food. The day roost is returned to before dawn arrives.

The big brown bat protects itself from predators by using roosts that are secluded. When the big brown bat pups fall out of the roost they are vulnerable to cats, raccoons and snakes. Owls and falcons sometimes catch the bats as they leave the roosts.

The male of the species lives longer than the females with the average lifespan being 19 years. The first winter is when most big brown bats die, if there isn’t enough stored fat they will not make it through the hibernation and will die in the hibernation roost.