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 and possessing a wingspan of .
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% The genus name, Eptesicus, is likely derived from the Greek words ptetikos ("able to fly") or petomai ("house flier"), and the species name "fuscus" is Latin in origin, meaning "brown". The big brown bat is the type species for the genus Eptesicus, which was established in 1820 by French-American naturalist Constantine Samuel Rafinesque. Though Rafinesque designated the type species as Eptesicus melanops, this was later determined to be a synonym of Eptesicus fuscus. The first use of the current name combination Eptesicus fuscus was in 1900 by Hungarian zoologist Lajos Méhelÿ. Recognized subspecies number eleven or twelve:
{| class="wikitable mw-collapsible" style="margin-left: auto; margin-right: auto; border: none;"
!Subspecies || Authority|| Type locality
|-
|E. f. bahamensis ||Gerrit Smith Miller Jr.|| Nassau, Bahamas
|-
| E. f. bernardinus || Samuel Nicholson Rhoads|| San Bernardino, California
|-
| E. f. dutertreus || Paul Gervais || Cuba
|-
| E. f. fuscus || Gerrit Smith Miller Jr.|| Constanza, Dominican Republic
|-
| E. f. lynni || Harold H. Shamel|| Montego Bay, Jamaica
|-
| E. f. miradorensis || Joel Asaph Allen || Veracruz, Mexico
|-
| E. f. osceola || R. T. Young|| Boulder, Colorado
|-
| E. f. peninsulae || Oldfield Thomas || Sierra de la Laguna, Mexico
|-
| E. f. petersoni|| Gilberto Silva Taboada || Isla de la Juventud, Cuba
|-
|E. f. wetmorei || Hartley H. T. Jackson || Maricao, Puerto Rico
|}
E. f. lynni has sometimes been considered a full species, though was listed as a subspecies by the American Society of Mammalogists and the Integrated Taxonomic Information System (ITIS) as of 2019. In the US state of Colorado where two subspecies were hypothesized to overlap (E. f. fuscus and E. f. pallidus), morphological features did not agree with genetic lineages, and thus were not reliable in distinguishing the two subspecies. Individuals with eastern and western US genetic lineages co-occurred in the same colonies, however. The serotinus group also includes:
- Little black serotine, E. andinus
- Botta's serotine, E. bottae
- Brazilian brown bat, E. brasiliensis
- Diminutive serotine, E. diminutus
- Argentine brown bat, E. furinalis
- Long-tailed house bat, E. hottentotus
- Harmless serotine, E. innoxius
- Meridional serotine, E. isabellinus
- Lagos serotine, E. platyops
- Serotine bat, E. serotinus
- Sombre bat, E. tatei
Description
thumb|A big brown bat baring teeth, illustrating the creature's dental formula.|alt=A small, fluffy mammal opens its jaws at the camera, reveal sharp teeth
It is a relatively large microbat, weighing . Adult body length is . Its wingspan is . Its dorsal fur is reddish brown and glossy in appearance; its ventral fur is lighter brown. Its snout, uropatagium (flight membrane between the hind limbs), and wing membranes are black and hairless. Its ears (
It has a robust skull; The snout has a rounded and somewhat flattened appearance.
Biology
Diet
thumb|right|200px|alt=A big brown bat, eating a mealworm|A big brown bat, eating a [[mealworm.]]
Big brown bats are insectivorous, eating many kinds of insects including beetles, flies, stone flies, mayflies, true bugs, net-winged insects, scorpionflies, caddisflies, and cockroaches.
Big brown bats are significant predators of agricultural pests. 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 bugsall of which cause serious agricultural damage.
Behavior
The big brown bat is nocturnal, roosting in sheltered places during the day. It will utilize a wide variety of structures for roosts, including mines, caves, tunnels, buildings, bat boxes, tree cavities, storm drains, wood piles, and rock crevices. Both solitary males and solitary, non-pregnant/non-lactating females have been found roosting under 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. Females exhibit philopatry ("love of place"), with 10-30% of female offspring returning to their natal roost the following year and up to 72% of adult females using the same roost in subsequent years. Using echolocation, big brown bats can determine how far away an object is, the objects size, shape and density, and the direction (if any) that an object is moving. Their use of echolocation allows them 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 species that may prey on the big brown bat itself.
Reproduction and life expectancy
Big brown bat mating season is in the fall. After the breeding season, pregnant females separate into maternity colonies around April. the big brown bat only has two nipples. At birth, pups are blind, helpless, and only , though they grow quickly, gaining up to per day. according to a 2008 report, some banded big brown bats have lived up to 20 years, although some experts have hypothesized that the bats might be "capable of living much longer." In general, males live longer than females. Big brown bats often hibernate by themselves, or in small groups. Big brown bats tolerate cold weather fairly well, although they can be negatively affected by major changes in temperature. The big brown bat has large deposits of brown fat, which provides the bats with a source of energy to rapidly increase body temperature upon arousal from hibernation. In the summer, big brown bats substantially reduce their brown fat deposits, which are less than half of their winter size.
Predators, parasites, and disease
The big brown bat has few natural predators. Predation occurs opportunistically, with common grackles, American kestrels, owls, long-tailed weasels, and American bullfrogs as known predators. Rabid big brown bats will bite each other, which is the primary method of transmission from individual to individual. However, not all individuals will develop rabies after exposure to the virus. Some individuals have been observed with a sufficiently high rabies antibody concentration to confer immunity. Rabies immunity can be passed from mother to pup via passive immunity or from exposure to the bite of a rabid individual. Overall, a low proportion of big brown bats become infected with rabies. Populations of big brown bats in the Eastern United States have a different strain of rabies than the populations in the Western United States. In one study, only 10% of big brown bats were shedding the rabies virus through their saliva before exhibiting clinical symptoms of the disease; symptoms of rabies in big brown bats include acute weight loss, paralysis, ataxia (inability to coordinate muscle movement), paresis (weakness of voluntary movement), and unusual vocalizations. It is found from southern Canada and Alaska to as far south as Colombia and Venezuela. It has also been documented in the Caribbean in both the Greater and Lesser Antilles, including Cuba, Hispaniola, Dominica, Barbados, and the Bahamas. The big brown bat has been documented from above sea level. It 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.
Relationship to people
The big brown bat is the official state mammal of the District of Columbia.
Economic value
thumb|right|A typical bat box affixed to a post|alt=The image depicts a small wooden box on a pole.
Big brown bats are a species that will use bat houses for their roosts. Landowners will purchase or construct bat houses and install them, hoping to attract big brown bats, largely due to their being an "agriculturally valuable species". In particular, the big brown bat feeds on cucumber beetles, which can decimate corn; this makes the species quite beneficial to farmers in the Corn Belt.
As disease vectors
Big brown bats can be of concern to public health as a rabies vector, as they commonly roost in buildings and thus have a higher chance of encountering humans. Big brown bats infrequently test positive for the rabies virus; of the 8,273 individuals submitted for testing across the United States in 2011, 314 (3.8%) tested positive for the virus. There is a known bias in testing, however, as healthy bats rarely come into contact with humans, and therefore sick bats are more likely to be tested. In the US, human rabies cases from exposure to bats more frequently come from other bat species. Of the twenty-four human rabies cases from bats from 1993 to 2000, seventeen cases (71%) were a rabies variant associated with the silver-haired bat (Lasionycteris noctivagans) while one case (4%) was associated with the rabies variant found in big brown bats.
Histoplasma capsulatum, the fungus that causes the disease histoplasmosis, is occasionally found in its guano. The big brown bat may also be a vector of the Saint Louis encephalitis virus, a mosquito-born virus that can affect humans.
See also
- Bats of Canada
- Bats of the United States
- Brown long-eared bat
- Little brown bat, a similarly named bat belonging to the Myotis genus