Eptesicus fuscus has a few predators, including owls, snakes, racoons, and even house cats (Kurta 1995). Also, man-made chemicals such as DDT and PCB can concentrate in milk, embryos, and adult tissue and may cause death. This bat can survive up to 19 years in the wild and males tend to live longer than females (Nowak 1991).
The heart rate of this bat shows some amazing range. For example, the heart rate can increase from 420-490 beats per minute (prior to flight), to 970-1097 beats per minute in flights of two to four seconds duration (Hill and Smith 1984).
The fossil record of the big brown bat is the most widespread Pleistocene bat in North America. Fossil records are known from more than 30 sites in the U.S. and Pleistocene fossils are also reported in Mexico, Puerto Rico, and the Bahamas (Kurta and Baker 1990).
Eptesicus fuscus is a colonial species of bat that is commonly found in Michigan. In this area, the dorsal pelage of the big brown bat appears brown to reddish brown, being evenly colored across the surface (Kurta 1995). It is the second largest bat in Michigan, the largest being Lasiurus cinereus, the hoary bat (Baker 1983). It inhabits rural areas, cities, and towns, and has the widest distribution of all bat species in Michigan. It is expected that the big brown bat inhabits all counties. (Baker 1983).
Baby bats who are separated from their mothers, either by falling from the roost, or by otherwise appearing lost, will squeak continuously. The squeaking can be heard from a distance of more than 30 feet. This communication is important for the baby's survival as it may help the mother locate and return them to a safer place. Bats also make a number of audible sounds, they squeak and hiss at each other in the roost
Perception Channels: tactile ; chemical
Conflicts with humans can occur when the bats enter dwellings. Bats can be kept from re-entering a home if the holes used as entrances are blocked. This is best done at night once the bats have left to hunt for food. It should not be done during June or July when there may be flightless young bats remaining in the home (Kurta 1995).
Since big brown bats are beneficial in consuming agricultural or nuisance pests, it has been suggested farmers should actually encourage the bats to form maternity colonies. A further suggestion would be to design bridges to encourage bats to use them as roosts (Whitaker 1995).
Big brown bats are fairly common and are not of any special conservation concern.
Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Many people do not like sharing their homes with bats. The only way to keep them from entering homes or other buildings is to block the holes bats use as entryways.
People also have concerns regarding bats and the virus which causes rabies, all mammals are susceptible to the disease. However it is important to caution that people should not handle any obviously sick wild animal. Also, the risk of contracting rabies from bats is exaggerated.
Negative Impacts: injures humans (carries human disease); causes or carries domestic animal disease ; household pest
Big brown bats are insectivorous. They consume many insect pests, including common threats to crop plants. They eat the corn root worm which may be the single most important agricultural pest in the United States (Whitaker 1995).
Positive Impacts: controls pest population
Eptesicus fuscus is an insectivorous bat. It preys primarily on beetles using its robust skull and powerful jaws to chew through the beetles' hard chitinous exoskeleton. It also eats other flying insects including moths, flies, wasps, flying ants, lacewing flies, and dragonflies (Baker 1983). One study indicated that juvenile E. fuscus ate a greater range of softer food items in their diets, compared to adults. The same study also indicated that bats having survived their first winter (yearlings), did not differ significantly in diet from the adults (Hamilton and Barclay 1998).
The big brown bat must confine its feeding activity to warm months when prey insects are active. Therefore it has to accumulate enough fat reserves, as much as one third of its body weight, before entering hibernation. Some estimate that these bats catch at least 1.4 grams of insects per hour (Baker 1983). Another study identified a single adult which gorged on food at a rate of 2.7 grams per hour (Davis et al 1963).
Like most other bats, E. fuscus does not feed in heavy rain or when the air temperature dips below 10 degrees centigrade. In good weather they will begin foraging 20 minutes after sunset. They eat until full, and then often make use of a "night roost". This means the bat will hang under a porch or in a barn to rest while digesting its meal. It returns to its day roost before dawn (Kurta 1995).
Primary Diet: carnivore
Eptesicus fuscus, also known as the Big Brown Bat, ranges from southern Canada, through temperate North America, down through Central America to extreme northern South America, and the West Indies (Nowak 1991).
Biogeographic Regions: nearctic (Native ); neotropical (Native )
The big brown bat inhabits cities, towns, and rural areas, but is least commonly found in heavily forested regions (Kurta 1995).
Some bats require stable, highly insulated environments in order to hibernate. Eptesicus fuscus has a more tolerant constitution so it can winter in less substantial structures. Besides human dwellings, it has been found to take up residence in barns, silos, and churches. Also, this bat has been found roosting in storm sewers, expansion joint spaces in concrete athletic stadiums, and copper mines (Baker 1983).
In presettlement times it is presumed the big brown bat roosted in tree hollows, natural caves, or openings in rock ledges. Occasionally groups of these bats are still found living in tree cavities (Baker 1983). Recently, some were found hibernating in caves in Minnesota (Knowles 1992).
The generic name Eptesicus is derived from the Greek, meaning "house flyer". All this bat needs is a small hole or warped, loose siding to gain entry into a home. Once inside, it prefers to roost in double walls or boxed-in eaves rather than attics. It is reasonable to speculate that populations of the big brown bat have increased with an increasing number of human habitations (Baker 1983).
Habitat Regions: temperate
Terrestrial Biomes: forest ; rainforest ; scrub forest
Big brown bats can survive up to 19 years in the wild and males tend to live longer than females. Most big brown bats die in their first winter. If they do not store enough fat to make it through their entire hibernation period then they die in their winter roost.
Range lifespan
Status: wild: 19.0 (high) years.
Average lifespan
Status: wild: 19.0 years.
Total length is 110-130 mm of which the tail is about 38-50 mm. Forearm length is 41-50 mm; hindfoot length is 10-14 mm. Height of the ears from the notch is 16-20 mm (Kurta 1995). The wingspan is about 330 mm (13 inches) (Baker 1983). This species is sexually dimorphic in size, females being slightly larger than males (Kurta and Baker 1990)
The skull is comparatively large and contains 32 teeth. The teeth are sharp, heavy, and were described as capable of causing severe bites. The bat's nose is broad and the lips are fleshy; the eyes are large and bright. The ears are rounded and the tragus is broad with a rounded tip (Baker 1983)
The tail is less than half the total body length and the tip projects slightly beyond the uropatagium. This bat also has a cartilaginous calcar which articulates with the calacaneum, and has a keel-shaped extension (Baker 1983)
Pelage color depends on location and subspecies. Dorsally, it ranges from pinkish tans to rich chocolates. The ventral fur is lighter, being near pinkish to olive buff. Some have described it as being "oily" in texture. The bat's naked parts of the face, ears, wings, and tail membrane are all black (Kurta and Baker 1990). Occasionally, E. fuscus has been found with white blotches on the wings, and some albino specimens are known as well (Baker 1983).
Range length: 110.0 to 130.0 mm.
Average wingspan: 330.0 mm.
Other Physical Features: endothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger
Average mass: 23 g.
Average basal metabolic rate: 0.113 W.
Big brown bats choose secluded roosts to protect themselves from many predators. Young are often taken from maternity roosts by snakes, raccoons, and cats if they fall. Flying bats are sometimes captured by owls and falcons as they leave their roosts.
Known Predators:
Big brown bats tend to mate right before they go into hibernation, but the female does not become pregnant until the spring, in the beginning of April. 60 days after the female becomes pregnant, she gives birth to one or two babies. The average weight of a pup is 3.3g. The babies are born blind and with no fur, but they grow quickly and are able to fly by early July.
Eptesicus fuscus employs delayed fertilization as a reproductive strategy. In males, spermatazoa are produced beginning in October. This species mates just prior to entering winter hibernacula, however, copulation can take place if individuals wake during hibernation. Sperm is stored in the female tract until the beginning of April, at that time ovulation and fertilization take place (Baker 1983).
The female gives birth to one or two young after a 60-day gestation period. At birth, the young is blind, naked, has closed eyes, and weighs about 3.3 g (Kurta 1995). The young grow rapidly, their eyes opening after about seven days. Female big brown bats have two mammary glands to nurse the young which are then weaned and ready to fly by late June or early July. They may reach adult size in August (Baker 1983). Males are not involved in parenting.
Breeding season: Late fall
Range number of offspring: 1.0 to 2.0.
Average gestation period: 60.0 days.
Range weaning age: 18.0 to 35.0 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous ; sperm-storing
Average birth mass: 3.9 g.
Average gestation period: 35 days.
Average number of offspring: 2.
Average age at sexual or reproductive maturity (male)
Sex: male: 730 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 547 days.
Females must eat at least their body weight in insects each night when they are nursing young. They leave the young in the roost while foraging.
Parental Investment: altricial ; female parental care
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 15–26 g (0.53–0.92 oz) and possessing a wingspan of 32.5–35 cm (12.8–13.8 in).
Big brown bats are insectivorous, consuming a diverse array of insects, particularly night-flying insects, but especially beetles.[4] 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%[5] of submitted big brown bats were positive for the rabies virus. Bat boxes are sometimes used to attract them as they are an agriculturally valuable species.
The big brown bat was described in 1796 by French naturalist Palisot de Beauvois. Palisot described the species based on specimens in the museum of Charles Willson Peale, an American naturalist, giving it the name Vespertila fuscus.[6][7] 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".[8] 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.[9] Recognized subspecies number eleven[10] or twelve:[11]
E. f. lynni has sometimes been considered a full species,[22][23] though was listed as a subspecies by the American Society of Mammalogists and the Integrated Taxonomic Information System (ITIS) as of 2019.[24][25] 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.[10]
As the genus Eptesicus is fairly speciose, it is further divided into morphologically similar "species-groups". The big brown bat belongs to the serotinus group, which is defined by having a large, elongate skull, flat braincase, and a long snout.[26] In a study of the evolutionary relationships of some Eptesicus species, the big brown bat was most closely related to the two other species from the Americas: the Argentine brown bat and the diminutive serotine.[27] The serotinus group also includes:[26]
It is a relatively large microbat, weighing 15–26 g (0.53–0.92 oz). Adult body length is 110–130 mm (4.3–5.1 in).[28] Its forearm is usually longer than 48 mm (1.9 in).[29] Its wingspan is 32.5–35 cm (12.8–13.8 in). 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 are also black;[28] they are relatively short with rounded tips.[29] The tragi (cartilage flaps in front of the ear canal) also have rounded tips.[28]
It has a robust skull;[29] the greatest length of the skull is approximately 19.25 mm (0.758 in).[30] The snout has a rounded and somewhat flattened appearance.[29] The braincase has a breadth of approximately 8.6 mm (0.34 in) and the mandible (jawbone) has a length of approximately 14.5 mm (0.57 in).[30] The upper incisors are large, with the inner pair more prominent than the outer pair. The inner pair of upper incisors also has a distinctive secondary cusp. The crowns of the lower incisors are trifid, or have three cusps.[29] Its dental formula is 2.1.1.33.1.2.3, for a total of 32 teeth.[31]
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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.[32][31] It will forage in cities around street lamps. As the big brown bat is such a widespread species, it has regional variation in its diet, though it is generally considered a beetle specialist. Populations in Indiana and Illinois have particularly high consumption of scarab beetles, cucumber beetles, ground beetles and shield bugs. In Oregon, primary prey items include moths in addition to scarab beetles and ground beetles. In British Columbia, large proportions of caddisflies are consumed, with flies as a secondary prey source.[33] A study in Ontario compared fecal samples of big brown bats with the abundance of insects collected in passive traps. The result was a strong preference for beetles as prey. Lepidoptera were the most common insect order collected but beetles were present in 99.2% of fecal samples.[32] When being rehabilitated, big brown bats are often fed mealworms which have been supplemented with necessary vitamins and minerals.[34]
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 bugs—all of which cause serious agricultural damage.[35]
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.[33] They generally roost in cavities, though they can sometimes be found under exfoliating bark.[36][37] Both solitary males and solitary, non-pregnant/non-lactating females have been found roosting under bark.[38] 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.[29]
Like many other species of microbats, the big brown bat often uses echolocation to navigate. This means that the species emits a call out into its environment and listens to the echoes of those calls that return from various objects near them.[39] 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.[40]
Big brown bat mating season is in the fall. After the breeding season, pregnant females separate into maternity colonies around April.[8][31] Maternity colonies range in size from 5-700 individuals, though in the eastern US and Canada, they are frequently 25-75 adults.[29] Historically, maternity colonies were probably in tree cavities. In modern, human-dominated landscapes, however, many maternity colonies are in buildings.[33] In the eastern United States, twins are commonly born sometime between May and July; in western North America, females give birth to only one pup each year.[29] A dissected female was once found with four embryos; had the female given birth, though, it is unlikely that all four would have survived.[31] Like most species of bat,[41] the big brown bat only has two nipples. At birth, pups are blind, helpless, and only 3 g (0.11 oz), though they grow quickly, gaining up to 0.5 g (0.018 oz) per day.[31] The pup nurses from its mother for approximately one month. Mothers leave their pups behind at the roost while they forage at night. Pups fledge, or begin flying, at three to five weeks old.[28]
A 2011 study of a population in Colorado found that their average life expectancy was a little over 6.5 years;[42] 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."[43] In general, males live longer than females.[29]
Big brown bats enter into hibernation around November, often in a location less than 80 km (50 mi) away from their summer roosts.[44] Big brown bats often hibernate by themselves,[44][45][46] or in small groups.[44][46] While some big brown bats hibernate in subterranean locations such as caves and underground mines,[29] most can be found in warm man-made structures.[47][48] Big brown bats tolerate cold weather fairly well,[45] although they can be negatively affected by major changes in temperature.[44] It is fairly common for some hibernating big brown bats to awaken temporarily and seek warmer shelter, locate water, and even mate.[8][44] Big brown bats come out of hibernation in the spring.[49]
The big brown bat has few natural predators. Depredation occurs opportunistically, with common grackles, American kestrels, owls, long-tailed weasels, and American bullfrogs as known predators.[29] It is affected by a number of ectoparasites (external parasites) and endoparasites (internal parasites). Insect ectoparasites include Basilia (flies), Cimex (true bugs), and Myodopsylla (fleas). Several mites are ectoparasites as well, including Acanthopthirius, Cheletonella, Euschoengastia, Leptotrombidium, Macronyssus, Neospeleognathopsis, Neotrombicula, Olabidocarpus, Ornithodoros, Parasecia, Perissopalla, and Spinturnix. Endoparasites include nematodes, cestodes, and trematodes.[29]
Like all bats in the United States,[50] big brown bats can be affected by rabies. The incubation period for rabies in this species can exceed four weeks,[51] though the mean incubation period is 24 days.[50] 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.[51] 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.[50]
The big brown bat is encountered widely throughout North America in present times.[29] 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 300–3,100 m (980–10,170 ft) above sea level.[1] It is a generalist, capable of living in urban, suburban, or rural environments.[33] 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.[29]
The big brown bat is evaluated at the lowest conservation priority by the IUCN—least concern. It meets the criteria for this designation because it has a wide geographic distribution, a large population size, occurrence in protected areas, and tolerance to habitat modification by humans.[1] While other bat species in the Eastern United States have experienced significant population declines (up to 98% loss) due to white-nose syndrome, the big brown bat is relatively resistant to its effects. Even in caves harboring Pseudogymnoascus destructans, the fungus that causes white-nose syndrome, big brown bats maintain normal torpor patterns. Unlike in other species more affected by white-nose syndrome, big brown bats are able to retain more of their body fat throughout hibernation. In fact, some regions of the eastern United States have seen an increase in big brown bat populations since the arrival of white-nose syndrome.[52]
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".[53] 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.[54]
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.[51] Because they are often found in proximity to humans, the big brown bat and the not-closely related little brown bat are the two bat species most frequently submitted for rabies testing in the United States.[55] 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.[5] 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.[56] 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.[57]
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.[29] Individuals have also tested positive for West Nile virus, which can also be transferred to humans via mosquitoes.[58]
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 15–26 g (0.53–0.92 oz) and possessing a wingspan of 32.5–35 cm (12.8–13.8 in).
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% of submitted big brown bats were positive for the rabies virus. Bat boxes are sometimes used to attract them as they are an agriculturally valuable species.
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