Animal Diversity Web

Ge­o­graphic Range

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

Habi­tat

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

Phys­i­cal De­scrip­tion

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).

• Other Physical Features
• endothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger

• Average mass

  23 g

  0.81 oz

  AnAge

• Range length

  110.0 to 130.0 mm

  4.33 to 5.12 in

• Average wingspan

  330.0 mm

  12.99 in

• Average basal metabolic rate

  0.113 W

  AnAge

Lifes­pan/Longevity

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

  Max Planck Institute for Demographic Research

Be­hav­ior

Fe­male big brown bats form ma­ter­nity colonies to rear young. The size of these colonies can vary from 5 to 700 an­i­mals. Males of the species roost alone or in small groups dur­ing this time. Both sexes will roost to­gether again in the late sum­mer (Nowak 1994).

One pub­lished study fo­cused on ma­ter­nity colonies roost­ing in build­ings in Ken­tucky. The data came from a group of 40 adult fe­males. They found that when the bats were in late preg­nancy, the fe­males were re­luc­tant to fly. Also, new­born young are not car­ried by the moth­ers dur­ing feed­ing flights, in­stead they are left be­hind in a clus­ter. Ap­par­ently, the mother only moves the young to trans­port them from one day roost to an­other (Davis et al 1968).

A mother Eptesi­cus fus­cus can rec­og­nize her own young after re­turn­ing to the clus­ter. In this study, the young bat tried to grab at any adult that came near it. The moth­ers crawled around among the group look­ing for their own young. Once found, the mother would lick the baby around the lips and face prior to nurs­ing (Davis et al 1968).

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 (Davis et al 1968).

The big brown bat hi­ber­nates in var­i­ous struc­tures, ei­ther man-made or nat­ural en­vi­ron­ments. They pre­fer cool tem­per­a­tures and can tol­er­ate con­di­tions many other bats can­not. They may be­come ac­tive dur­ing their win­ter hi­ber­nac­ula and can move to an op­ti­mum habi­tat. One banded bat was recorded to have moved to a dif­fer­ent cave 400 yards away, dur­ing the same win­ter (Goehring 1972).

The stim­uli that cause mam­mals to hi­ber­nate are not well un­der­stood, how­ever, in bats it seems that de­creas­ing am­bi­ent tem­per­a­ture is the pri­mary fac­tor. The fail­ure to ac­cu­mu­late enough fat for a long win­ter is a major mor­tal­ity fac­tor par­tic­u­larly for younger, less ex­pe­ri­enced bats (Kurta 1995). The bat's cir­cu­la­tion sys­tem slows con­sid­er­ably and oxy­gen con­sump­tion and heart rate are greatly re­duced. Heart rate in tor­por is 4 to 62 beats/minute, at 5 de­grees centi­grade. Heart rate dur­ing arousal from hi­ber­na­tion in­creases from about 12 to 800 beats per minute (Kurta and Baker 1990). By the end of this hi­ber­na­tion pe­riod, the bat may have lost up to 25% of its weight prior to hi­ber­na­tion (Fen­ton 1983).

One study of the big brown bat found it was ca­pa­ble of hi­ber­nat­ing for 300-340 days. It was kept in a re­frig­er­a­tor at a con­stant low tem­per­a­ture, pro­vided only with water (Hill and Smith 1984).

In the 1930s, echolo­ca­tion pi­o­neer Don­ald R. Grif­fin took some bats, in­clud­ing E. fus­cus, into a lab which had a mi­cro­phone sen­si­tive to ul­tra­sonic sound. He used a bat­tery of ex­per­i­ments to show that the bats used the echoes of their calls to lo­cate ob­sta­cles (echolo­ca­tion) (Fen­ton 1983). Since then it has been found that echolo­ca­tion calls in bats often in­clude fre­quency mod­u­lated (FM) and con­stant frquency (CF) com­po­nents. In E. fus­cus there is a short FM sig­nal (1-5 ms) that sweeps down­ward from 50 kHz to 25 kHz, the CF por­tion is often deleted or short­ened (Hill and Smith 1984).

This bat uti­lizes echolo­ca­tion to avoid ob­sta­cles and to cap­ture fly­ing in­sect prey. It can track in­sects into veg­e­ta­tion and in­ter­cept them while also avoid­ing the ob­sta­cles veg­e­ta­tion may pre­sent (Sim­mons et al 1996). These bats emit vol­leys of calls through their open mouths. The du­ra­tion of each call and in­ter­val be­tween calls varies de­pend­ing on whether the bat is in search, ap­proach, at­tack, or ter­mi­nal phase. They are able to get acoustic im­ages by in­te­grat­ing in­for­ma­tion from echoes in re­la­tion to their out­go­ing calls (Nowak 1991).

Typ­i­cally, in­sec­tiv­o­rous bats will in­crease the rate of echolo­ca­tion calls as they close in on prey. The calls ter­mi­nate in what is de­scribed as a "feed­ing buzz", a high pulse rep­e­ti­tion rate as­so­ci­ated with an at­tack on prey (Nowak 1991).

Some data sug­gest big brown bats for­age ori­ent to­ward the loud­est nat­ural sound fields. This tends to cor­re­late with high den­si­ties of in­sect prey. They were able to de­tect cho­rus­ing cricket frogs and katy­dids over hun­dreds of me­ters away (Bucher and Childs 1981). An­other study showed these bats were first able to de­tect 19 mm di­am­e­ter spheres at 5.1 me­ters and 4.8 mm spheres at 2.9 me­ters (Al­tring­ham 1996). Nu­mer­ous stud­ies have been done in con­nec­tion with the big brown bat's echolo­cat­ing ca­pac­i­ties and it is worth fur­ther read­ing to un­der­stand the depth and sen­si­tiv­ity of their abil­i­ties.

• Key Behaviors
• nocturnal
• motile
• migratory
• social

Com­mu­ni­ca­tion and Per­cep­tion

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

Food Habits

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

Pre­da­tion

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

  • owls (Strigiformes)
  • snakes (Serpentes)
  • raccoons (Procyon lotor)
  • domestic cats (Felis silvestris)
  • falcons (Falconidae)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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

Con­ser­va­tion Sta­tus

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%. (Cryan, 2010; Na­tional Park Ser­vice, Wildlife Health Cen­ter, 2010)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Other Com­ments

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).

Con­trib­u­tors

Michael Mul­heisen (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Kath­leen Berry (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Phil Myers (ed­i­tor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

Ar­ling­ham, J. 1996. Bats, Bi­ol­ogy and Be­hav­iour. Ox­ford Uni­ver­sity Press.

Baker, R. 1983. Michi­gan Mam­mals. Lans­ing, Michi­gan, USA: Michi­gan State Uni­ver­sity Press.

Buch­ler, E., S. Childs. 1981. Ori­en­ta­tion to Dis­tant Sounds by For­ag­ing Big Brown Bats (Eptesi­cus Fus­cus). An­i­mal Be­hav­iour, 29,2: 428-432.

Cryan, P. 2010. "White-nose syn­drome threat­ens the sur­vival of hi­ber­nat­ing bats in North Amer­ica" (On-line). U.S. Ge­o­log­i­cal Sur­vey, Fort Collins Sci­ence Cen­ter. Ac­cessed Sep­tem­ber 16, 2010 at http://​www.​fort.​usgs.​gov/​WNS/​.

Davis, W., R. Bar­bour, M. Has­sell. Feb­ru­ary 1968. Colo­nial Be­hav­ior of Eptesi­cus Fus­cus. Jour­nal of Mam­mal­ogy, Vol 4, No. 1: pp. 44-50.

Fen­ton, B. 1985. Com­mu­ni­ca­tion in the Chi­roptera. Bloom­ing­ton: In­di­ana Uni­ver­sity Press.

Fen­ton, B. 1983. Just Bats. Toronto: Uni­ver­sity of Toronto Press.

Goehring, H. Feb­ru­ary 1972. Twenty-Year Study of Eptesi­cus Fus­cus in Min­nesota. Jour­nal of Mam­mal­ogy, Vol. 53, No.1: pp. 201-207.

Hamil­ton, I., R. Bar­clay. Aug 1998. Diets of Ju­ve­nile, Year­ling, and Adult Big Brown Bats (Eptesi­cus fus­cus) in South­east­ern Al­berta. Jour­nal of Mam­mal­ogy, 79:(3): 764-771.

Knowles, B. Apr-Jun 1992. Bat Hi­ber­nac­ula On Lake Su­pe­ri­ors North Shore, Min­nesota. Cana­dian Field Nat­u­ral­ist, 106:(2): 252-254.

Kurta, A. 1995. Mam­mals of the Great Lakes Re­gion. Ann Arbor: The Uni­ver­sity of Michi­gan Press.

Kurta, A., R. Baker. 26 April 1990. Eptesi­cus fus­cus. Mam­malian Species: No. 356, pp.1-10.

Na­tional Park Ser­vice, Wildlife Health Cen­ter, 2010. "White-nose syn­drome" (On-line). Na­tional Park Ser­vice, Wildlife Health. Ac­cessed Sep­tem­ber 16, 2010 at http://​www.​nature.​nps.​gov/​biology/​wildlifehealth/​White_​Nose_​Syndrome.​cfm.

Sim­mons, J., M. Fer­rag­amo, T. Hare­sign, J. Fritz. Aug 1996. Rep­re­sen­ta­tion of Per­cep­tual Di­men­sions of In­sect Prey Dur­ing Ter­mi­nal Pur­suit by Echolo­cat­ing Bats. Bi­o­log­i­cal Bul­letin, 191:(1): 109-121.

Whitaker, J. Oct 1995. Food of the Big Brown Bat Eptesi­cus-Fus­cus From Ma­ter­nity Colonies In In­di­ana And Illi­nois. Amer­i­can Mid­land Nat­u­ral­ist, 134:(2): 346-360.

Whitaker, J., S. Gum­mer. May 1992. Hi­ber­na­tion of the Big Brown Bat, Eptesi­cus-Fus­cus, in Build­ings. Jour­nal of Mam­mal­ogy, 73:(2): 312-316.