Big Brown Bat
Eptesicus fuscus
Summary 2
The big brown bat (Eptesicus fuscus) is native to North America, Central America, the Caribbean, and extreme northern South America.
Conservation status 3
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
Description 4
Big brown bats make their homes in rural areas, towns, and cities, sometimes choosing barns, houses, or other buildings as roosts. Males usually live alone; females gather in maternity colonies in the spring and summer to give birth and raise their young. A maternity colony may include 20 - 75 adults and their offspring. Females in the eastern United States usually give birth to twins; those in the West usually have a single pup each year. Females may return to the same colony year after year. On warm, dry evenings, the bats leave the roost shortly after sunset to forage for insects especially flying beetles which they catch and eat in the air. When the weather is cold or wet, they may stay in the roost, dropping their body temperature and living on stored fat. In the winter, they hibernate. Many migrate a short distance (less than 80 km) to find mines or caves for hibernation, but some spend the winter in attics or walls where the temperature is cool but stays above freezing.
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Distribution 5
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 )
Food habits 6
Big brown bats are insectivores, eating mostly Coleoptera. They will also eat other flying insects including Lepidoptera, Diptera, Hymenoptera, and others. They use their strong teeth to chew though the hard outer shell of the insects. Big brown bats only eat in warm months when insects are alive. Therefore, they eat large amounts of insects in the summer and fall to prepare for hibernation. They will also not eat in heavy rain or if the temperature gets too low. They usually begin looking for food right after sunset, eat until they are full, then hang upside down to digest their meal. They return to the day roost during sunlight hours.
Habitat 7
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
Reproduction 8
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
Sources and Credits
- (c) Juan Cruzado Cortés, some rights reserved (CC BY-SA), uploaded by Juan Cruzado Cortés
- Adapted by rkkessler from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Eptesicus_fuscus
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31393151
- (c) Smithsonian Institution, some rights reserved (CC BY), http://eol.org/data_objects/6624840
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31393141
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/25064729
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31393142
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31393144
