Art Credit: Sahina Irvin
Appearance
Photo courtesy of USFWS/Ann Froschauer
The big brown bat is relatively large, weighing in at 11-23 grams (or about as much as 1-2 half dollar coins), with a wingspan about 13 inches across (Marks and Marks 2006). This species has long, silky fur on its back that is usually a chocolate brown color, with lighter brown fur on its belly. They have a large head with 32 teeth and a broad nose, with short, black, hairless rounded ears (WDNR 2013). The wing membranes are dark brown to black (FBC 2005).
Behavior
Photo by Merlin Tuttle used with permission
The Big Brown Bat is an insectivore, which means it primarily eats insects. It usually feeds on beetles, but will also eat flies, mosquitoes, and moths (Agosta 2002). Because of their strong head and jaw structure, this species is especially adapted to consuming hard-shelled beetles, making them an important predator of many agricultural pests. Big brown bats will hunt and feed year-round in Florida (Ober et al., 2016) and are not picky about choosing feeding grounds. When they emerge each night, they orient towards the direction of the loudest insect sounds, regardless of the kind of habitat (Bucher and Childs 1981). They begin their hunting flights about 20 minutes after sunset, eat until full, then find a “night roost,” where they rest for several hours to digest their food before returning to their main roost before dawn (Kurta 1995). Like most bats, the species uses echolocation to find prey, frequently emitting high-pitched calls and listening to the echo to home in on an insect’s exact location (Simmons et al. 1996). In the 1930s, big brown bats were among the first bat species discovered using echolocation to navigate and hunt (Fenton 1983).
Mating typically occurs during the fall and into winter, though it may sometimes also occur in spring. In winter, males and females usually roost individually or sometimes in small numbers. Though mating occurs in the fall, females can delay actual fertilization. Pregnancy does not occur until early spring. After winter, females will form maternity colonies for raising their pups. These colonies can range in size from 5-700 individuals, though usually consist of 25-75 bats. During this maternity season, males roost alone or in small groups (Miller et al. 2016). After two months gestation, females in Florida usually give birth to two pups in May or June (FBC 2005). Big brown bats have been recorded living as long as 20 years in the wild, though the average lifespan is likely much shorter (O’Shea et al. 2011).
Habitat
The big brown bat is believed to occur throughout Florida but may be rare in Southern Florida (Marks and Marks 2006). It can live in many different habitats. Though it often prefers forested area, the big brown bat can be found in cities, towns, rural areas, and many natural ecosystems, (Kurta 1995). The species tolerates a relatively wide range of temperatures, meaning it can roost in many kinds of structures. In the late spring and summer, big brown bats form maternity colonies beneath loose bark and in small tree cavities. They have also been documented in buildings, caves, mines, tree and rock crevices, storm sewers, stadiums, bat boxes, and many other kinds of structures (Agosta 2002, Baker 1983). While big brown bats can migrate hundreds of miles, the Florida populations tend to be year-round residents.
Threats
Many bats that roost in caves are facing the disease called white-nose syndrome (WNS). WNS is caused by the fungus Pseudogymnoascus destructans and has spread across North America (U.S. Fish and Wildlife Service [USFWS] 2020). White-nose syndrome causes widespread death in some cave bat populations by disrupting hibernation, causing individuals to wake more frequently and use up fat reserves (Frick et al. 2010, 2015; Lorch et al. 2011; Warnecke et al. 2012). Fortunately, big brown bats are largely resilient against WNS. Pseudogymnoascus destructans (Pd), the fungus that causes WNS, has been detected on big brown bats, but no actual symptoms have been documented. In caves with a known presence of Pd, big brown bats show normal behavior (Frank et al. 2014).
However, WNS is not the only disease threat to big brown bats. Gammaherpesvirus is a disease-causing virus that has been discovered in the lungs of big brown bats (Subudhi et al. 2018). The virus attacks the lymphatic system and is associated with cancer. Not much is known about the impacts of the virus on this species, but a recent study found a concerning lack of antibodies in bats that were infected (Subudhi et al. 2018).
While big brown bats have few natural predators due to their relatively secluded roosts, young are often taken from maternity roosts by snakes, raccoons, and cats if they fall. Flying adult bats are also sometimes captured snakes as they leave their roosts, and by owls and falcons.
Conservation and Management
These bats are monitored with the other bat species in Florida as part of the Long-term Bat Monitoring Program, which seeks to keep track of bat populations throughout the state. The program achieves this by placing ultrasonic detectors across the state that pick up and record calls of nearby bats. In addition, FWC performs yearly surveys of caves to check for the fungus that causes white-nose syndrome.
It is illegal to remove bats from structures or to otherwise handle them directly in the state of Florida. If you have bats in your house or other structure, please see our Living With Bats page to learn how to properly evict them.
How You Can Help
We are always glad to have volunteer help with our bat conservation work, particularly with the Long-term Bat Monitoring Program in which volunteers help place and monitor our acoustic detectors. If you are interested in volunteering with this program or in helping in other ways, please visit our Bat Force website to learn more.
References
Agosta, S. J. (2002) Habitat use, diet and roost selection by the big brown bat (Eptesicus fuscus) in North America: a case for conserving an abundant species. Mammal Review 32: 179-198.
Baker, R. H. (1983). Michigan mammals. 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.
Fenton, B. 1983. Just Bats. Toronto: University of Toronto Press.
Florida Bat Conservancy. (2005) Big Brown Bat. Retrieved from https://www.floridabats.org/big-brown-bat.html
Frank, C. L., Michalski, A., McDonough, A. A., Rahimian, M., Rudd, R. J., & Herzog, C. (2014). The resistance of a North American bat species (Eptesicus fuscus) to white-nose syndrome (WNS). PLoS One, 9(12), e113958.
Kurta, A. 1995. Mammals of the Great Lakes Region. Ann Arbor: The University of Michigan Press.
Kurta, A., & Baker, R. H. (1990). Eptesicus fuscus. Mammalian species, (356), 1-10.
Marks, C. S., & Marks, G. E. (2006). Bats of Florida. The University Press of Florida.
Miller, B., Reid, F., Arroyo-Cabrales, J., Cuarón, A.D. & de Grammont, P.C. (2016) Eptesicus fuscus. The IUCN Red List of Threatened Species 2016: e.T7928A22118197. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T7928A22118197.en
Ober, H., Main, M., & Allen, G. (2016) Bats of Florida. WEC186. Gainesville: University of Florida Institute of Food and Agricultural Sciences. Retrieved from http://edis.ifas.ufl.edu/pdffiles/UW/UW20300.pdf
O'Shea, T. J., Ellison, L. E., & Stanley, T. R. (2011). Adult survival and population growth rate in Colorado big brown bats (Eptesicus fuscus). Journal of Mammalogy, 92(2), 433-443.
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.
Subudhi, S., Rapin, N., Dorville, N., Hill, J. E., Town, J., Willis, C. K., Bollinger, T. K., & Misra, V. (2018). Isolation, characterization and prevalence of a novel Gammaherpesvirus in Eptesicus fuscus, the North American big brown bat. Virology, 516, 227-238.
Wisconsin Department of Natural Resources. (2013) Wisconsin Big Brown Bat Species Guidance. Bureau of Natural Heritage Conservation, Wisconsin Department of Natural Resources, Madison, Wisconsin. PUB-ER-707.