Art Credit: Sahina Irvin
Appearance
The southeastern myotis, also called the southeastern bat, is a small bat, weighing 5-8 grams (about the same as 2-3 pennies) and with a wingspan of 9-10.5 inches (24-27 cm) (Marks and Marks 2006). They range in color from gray to brown to a bright orange-brown on the back with a tan/white belly (LaVal 1970, Gardner et al. 1992). Their ears can be as long as 0.6 inches (15 mm) (Reynolds and Mitchell 1998). The southeastern myotis can be distinguished from other closely related bats by its long toe hairs that extend past the claws (Jones and Manning 1989).
Behavior
Like all Florida bats, the southeastern myotis is insectivorous, meaning it eats insects. Specifically, these bats prefer midges, mosquitoes, small moths and beetles, and crane flies (Whitaker and Hamilton 1998). Research from the University of Florida has found that 61% of all the species the bats eat are considered agricultural pests. The researchers also found a high proportion of mosquitoes in their diet (Hughes et al. 2021, Hughes et al. 2022). Southeastern myotis hunt insects by flying very low over bodies of freshwater, usually within 2 feet (60 cm) of the surface. They catch their prey in flight, a behavior known as “hawking” (Whitaker and Hamilton 1998). Like most bats, the species uses echolocation to find its prey, frequently emitting high-pitched calls and listening to the echo to home in on an insect’s exact location (Simmons et al. 1996).
Southeastern myotis mate in late winter and early spring, from February to April. Female southeastern myotis form large maternity colonies where they give birth to pups in late April to mid-May. Unlike other closely related species, southeastern myotis give birth to twins (Marks and Marks 2006). The pups are born helpless but learn to fly within 6 weeks of birth. Males tend to roost separately, either alone or in small “bachelor” colonies (Whitaker and Hamilton 1998). Florida populations of southeastern myotis rarely hibernate in winter and are active on most nights when conditions are suitable (McNab 1974). They typically live 4-8 years in the wild, but there are records of individuals living to 21 years (Nowak 1999).
Habitat
Southeastern myotis roost in many kinds of natural and human structures. The largest colonies are often found roosting in caves across North and Central Florida, and can have as many as 90,000 bats (Gore and Hovis 1998). Caves provide the bats with warm, stable temperatures and high humidity, which is important during the winter maternity season when bats give birth and raise young. Southeastern myotis choose long, deep roosting caves with a large domed room to trap heat (Smith et al. 2021). Southeastern myotis can also be found roosting in live hollow trees with large cavities at the base, particularly black gum, water tupelo, and sweetgum, and bald cypress (Horner and Mirowsky, 1996; Clark et al., 1997; Mirowsky and Horner, 1997; Hoffman, 1999). These trees are often found in bottomland hardwood forests. Southeastern myotis also roost in a variety of human structures including culverts, attics, bridges, barns, and bat houses (Mauk-Cunningham & Jones. 1999, Smith et al. In press). Regardless of where they roost, the species usually hunts over water (Whitaker and Hamilton 1998). However, in dry areas of Florida they are also known to hunt around live oaks and over small wood lots and shrubby old fields (Zinn and Humphrey, 1981; Humphrey and Gore, 1992).
Threats
One of the largest threats to southeastern myotis is roost loss. Caves suitable to support large maternity colonies to raise young are limited. In 1991, surveys of 19 caves previously known to support colonies of southeastern myotis found that only 9 remained active (Gore and Hovis 1998). These colonies were lost due to the closure of the entrances by landowners, clearing of the surrounding forest, and/or disturbance and vandalism (Gore and Hovis 1998). These types of disturbances can cause females in a maternity colony to abandon their young (Mumford and Whitaker 1982). A cave that supported up to 11,000 individual bats was completely abandoned following the development of a public dump site nearby. Since the early 1990s, at least two large maternity colonies have also been lost due to cave flooding.
Deforestation is another major threat to southeastern myotis, as it results in the loss of valuable food and roosting habitat (Erickson and West 1996). Increased storms associated with climate change also threatens southeastern myotis by knocking down many of the available roost trees.
Another potential threat to southeastern myotis is a 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 cycles, causing individuals to wake more frequently and use up fat reserves (Frick et al. 2010, 2015; Lorch et al. 2011; Warnecke et al. 2012). Luckily, WNS has not been detected in southeastern myotis yet, but we believe it may still be vulnerable to the disease due to its spread in other closely related species, as well as the presence of southeastern myotis in cave environments. WNS has not yet been detected in Florida, but it does occur in both neighboring states, Georgia and Alabama.
Conservation and Management
The southeastern myotis is one of Florida's Species of Greatest Conservation Need. 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.
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
Clark, M.K., E. Hajnos, and A. Black. 1997. Radio-tracking of Corynorhinus rafinesquii and Myotis austroriparius in South Carolina. Bat Research News 38: 136-137.
Frick WF, Pollock JF, Hicks AC, Langwig KE, Reynolds DS, Turner GG, Butchkoski CM, Kunz TH. 2010. An emerging disease causes regional population collapse of a common North American bat species. Science 329:679–682.
Frick WF, Puechmaille SJ, Hoyt JR, Nickel BA, Langwig KE, Foster JT, Barlow KE, Bartonicka T, Feller D, Haarsma A, Herzog C, Horacek I, van der Kooij J, Mulkens B, Petrov B, Reynolds R, Rodrigues L, Stihler CW, Turner GG, Kilpatrick AM. 2015. Disease alters macroecological patterns of North American bats. Global Ecology and Biogeography
Gardner, J., Hofmann, J., Garner, J., Krejca, J. and Robinson, S. 1992. “Distribution and status of Myotis austroriparius (southeastern bat) in Illinois.” Final Report. Illinois Natural History Survey and Illinois Department of Conservation, Springfield, Illinois, USA.
Gore, J. and Hovis, J. 1998. Status and conservation of southeastern myotis maternity colonies in Florida caves. Florida Scientist 61:160-170.
Hoffman, V.E. 1999. Roosting and relative abundance of the southeastern myotis, Myotis austroriparius, in a bottomland hardwood forest. MS thesis, Arkansas State University, Jonesboro.
Horner, P., and K. Mirowsky. 1996. East Texas rare bat survey: 1995. Final Report to Texas Parks and Wildlife Department, Resources Protection Division, Austin, Texas.
Hughes M, Braun E, Ober H. “Big bats binge bad bugs: Variation in crop pest consumption by common bat species.” Agriculture Ecosystems and Environment 314(7):107414. (2021)
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LaVal, R. “Infraspecific relationships of bats of the genus Myotis austroriparius.” Journal of Mammalogy 51:542-552 (1970)
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Marks, C. S., and G. E. Marks. Bats of Florida. 2006. University Press of Florida. Gainesville, Fl. 176 pp.
Mauk-Cunningham, C., C. Jones. 1999. Southeastern myotis (Myotis austroriparius). Pp. 83-85 in D Wilson, S Ruff, eds. The Smithsonian Book of North American Mammals. Washington, D.C. and London: The Smithsonian Insitution Press.
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Reynolds, L. A, and W.A. Mitchell. U.S. Army Corps of Engineers. 1998. Species Profile: Southeastern Myotis (Myotis Austroriparius) on Military Installations in the Southeastern United States. 1–30.
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Smith, L.M., T.J. Doonan, and J.A. Gore. 2024. Bats roost in culverts during hibernation and maternity season in North Florida. Journal of North American Bat Research. In press.
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