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Big Brown Bat (Eptesicus fuscus)

Big Brown Bat
Eptesicus fuscus
(Order Chiroptera; Family Vespertilionidae)

Adult Big Brown Bat. Photo courtesy of:

Adult Diagnosis: The big brown bat is fairly large compared to other bat species.  It has a body length 10-13 cm and a wingspan of 28-33 cm.  It weighs usually around 14 grams.  The wing membranes, face, and feet are dark brown to near black.  It has long brown fur.  

The species is an old group evolutionarily speaking, with fossil records dating back fifty million years. Big brown bats navigate through the dark with the use of echolocation.  They produce ultrasonic sounds through their mouths or nose, wait for the sound to bounce back from any objects, alerting the bat of potential prey or to simply avoid crashing.  

Juvenile Big Brown Bat (left) and adult in flight (right). Photo of juvenile courtesy of: of flight courtesy of:

Adult Natural History:  The big brown bat mates from November through March; this is known as swarming. Sperm is transferred to the female during mating; however fertilization of the egg is delayed until after hibernation in the spring.  After the breeding season, females seperate themselves from the males, forming a maternal community.

Distribution: Big brown bats can be found throughout the United States and southern Canada.  The bat takes up residence all year round, although in the summer months it may live 80 km from its winter roosts.  The big brown bat can be found in nearly all habitats, including meadows, deserts, alpine, forests, and even urban areas.  

Distribution of the Big Brown Bat. Purple indicates permanent residence. Map courtesy of:

Habitat: During late spring, summer, and early fall big brown bats can be found near water, in fields or forest, as well as urban and suburban areas.  The bats have two primary types of habitat: hibernation sites that they use during the winter, such as caves.  The other type of site the bats use are roosting sites for reproduction, such as forests and even buildings.  These roosting sites are primarily used during the summer.  

Diet:  Big brown bats are insectivores.  They primarily consume nocturnal flying insects such as wasps, moths, and beetles that they catch in flight.   

Big Brown Bat hunting prey. Photo courtesy of:

Conservation Status:  Least Concern    

Videos:   "Big Brown Bat" speaker at a bat conservatory.  


General information     

Geographic range/habitat    

Differences between species    


Eiting, T.P. and G.F. Gunnell. 2009. Global completeness of the bat fossil record. Journal of Mammalian Evolution 16:151-173.   

Gerardo, H.; Hobson, Keith A.; Adriana, M. A; Daniel, E. B; Sanchez-Corero, Victor; German, M. C. (2001). "The Role of Fruits and Insects in the Nutrition of Frugivorous Bats: Evaluating the Use of Stable Isotope Models". Biotropica 33 (3): 520–28.   

Hodgkison, Robert; Balding, Sharon T.; Zuibad, Akbar; Kunz, Thomas H. (2003). "Fruit Bats (Chiroptera: Pteropodidae) as Seed Dispersers and Pollinators in a Lowland Malaysian Rain Forest". Biotropica 35 (4): 491–502.

Submitted by: Michael O'Connell, August 2013

Wichita State University
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