Big Brown Bat: Eptesicus fuscus

The Big Brown Bat (Eptesicus fuscus) is one of the more common species of bat found in North American houses, barns, and other buildings. These animals play a vital role in the ecosystem of many areas, and help to manage the populations of insects in these locations.

As the name suggests, the Big Brown Bat is a larger than average species of bat that a sleek brown fur over most of its body. The wingspan of the bat can range between eleven and thirteen inches in most cases, with the body being no more than eight inches in length. The female Big Brown Bat is slightly larger than the male, but despite this the largest specimens will rarely weight more than 5/8 an ounce. These bats often form maternity colonies, but the numbers are usually less than the Little Brown Bat, which can form huge groups. The biology of the Big Brown Bat offers a number of different methods of communication for the animal, and the nasal glands of the bat allow them to emit a number of different chemical signals. Like other bats, the Big Brown Bat is a nocturnal animal, and uses echolocation while flying, which allows it to identify its prey in mid air.

The range of the Big Brown Bat is quite significant, with the species able to adapt to living in most parts of North America, with known populations of the species ranging from northern Mexico all the way up into Canada. However, the Big Brown Bat is more common in the northern half of the USA, with fewer colonies to be found in the southern states, particularly in Texas and Florida. When you get down to those states, you're more likely to find the Mexican Freetail Bat. The Big Brown Bat does show a preference for roosting in areas closer to the water, and they will always look for somewhere dark and cool where they can sleep during the day. This means that they will often be found roosting in caves and in the attic spaces of buildings, and will often look for more secluded quiet roosts for their hibernation from late September onwards. The Big Brown Bat is generally a species to be found in rural areas, but this adaptable species can survive in urban or suburban areas where there are parks or gardens where insects can be found.

The Big Brown Bat is an insectivore, and will eat almost any flying insect that it can catch. For this purpose, the bat has 38 small sharp teeth with which it can eat any small flying insect. Although the bat will catch many of these flying insects in its mouth, it can also net insects with its tail membrane, which it can then transfer into the mouth in flight. All of the Big Brown Bat’s hunting is done during twilight and in the night, and insects such as midges, gnats, mosquitoes, mayflies and moths are all potential prey. A swift digestive system means that the Big Brown Bat can eat up to 600 insects in an hour of hunting. And no, these bats are not blind, they can see fine, but they use echolocation to help them catch insects on the wing in the dark of the night.

The Reproductive Cycle
The mating season for the Big Brown Bat generally happens in September and October, in the period leading up to hibernation. This will generally happen as the bats swarm at the entrances of the hibernation roosts, although it is also known that a male awaking from its torpor during hibernation may also mate with a female during her hibernation. The sperm of the bats is then stored until the spring, when fertilization occurs. The females will join large nursery colonies in the spring, which can number thousands of female bats, and will give birth to one or sometimes two bats in June or July. For the first few hunting flights the baby will often cling to the teat of its mother during flight, although after a few weeks it will then be left at the colony. After around a month these young bats are weaned and capable of flight, and the mother will leave the nursery colony. Females will often be ready to breed after one year, while the male will begin mating in its second year. Although small, the Big Brown Bat can live to over ten years of age in the wild.

White Nose Syndrome
Because of the tendency to roost in colonies, the Big Brown Bat population is particularly at risk to White Nose Syndrome, which is a fungal disease which has killed many thousands of bats in North America. This fungus is identified by the white traces left on the noses of a number of different species of bats that live in caves, and has decimated many colonies of the Big Brown Bat.

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