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
