Header Photo by Ann Froschauer/U.S. Fish and Wildlife Service
Appearance
The Brazilian free-tailed bat, also known as the Mexican free-tailed bat, is a medium-sized species of bat found throughout Florida. It is the state’s most common bat species. It weighs around 7-12g (about the same as 1-2 quarters) and has a wingspan of roughly 12 inches (Marks and Marks 2006). Females are usually a bit heavier than males so they can store extra fat they need for reproduction (Wilkins 1989). Their fur color can range from dark brown to gray and they have distinctly deep wrinkles on their cheeks (Marks and Marks 2006). Their tails stick out beyond the membrane stretching between their hind legs (called the “uropatagium”), giving them their common name of “free-tailed” bat.
Behavior
Like all Florida bats, the Brazilian free-tailed bat is insectivorous, which means they eat insects. Their diet is mostly moths and beetles, but they will also eat mosquitoes, wasps, and other flying insects (McWilliams 2005). These bats leave their roosts shortly before sunset to hunt for food, flying at much higher altitudes than other bat species, sometimes as high as 10,000 feet (Williams et al. 1973). Like most bats, Brazilian free-tailed bats use echolocation to find their prey. By frequently emitting high-pitched calls and listening to the echo, they can home in on an insect’s exact location as they fly by. They can even adjust the frequency and strength of the calls at different altitudes (Gillam et al. 2009). The Brazilian free-tailed bat is the fastest known bat, recorded flying as fast as 99mph (McCracken et al. 2016).
Female Brazilian free-tailed bats gather in large maternity roosts during the breeding season, which runs from March through July. After a gestation period of 11-12 weeks, pups are typically born in June or July (Marks and Marks 2006). Females will usually give birth to a single pup, though rarely they may have twins. Weaning occurs 4-7 weeks after birth, at which point the pups become independent (Kunz and Robson 1995). These bats live several years, with the longest reported lifespan in captivity at 12 years (Wiegle 2005).
Habitat
Merlin Tuttle photo used with permission
In Florida, the Brazilian free-tailed bat prefers to roost in human structures such as attics, sheds, under bridges, and in bat houses. They are also rarely found roosting in palm trees. Elsewhere in their range, this species is cave dwelling. However, Florida’s caves are probably too humid for their preferences (Wilkins 1989).
Threats
The biggest threat to Brazilian free-tailed bats in Florida is conflict with humans. Because they do not roost in caves in Florida, Brazilian free-tailed bats will often roost in human structures instead, often leading to conflict and exclusions.
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.
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
Gillam, E. H., McCracken, G. F., Westbrook, J. K., Lee, Y. F., Jensen, M. L., & Balsley, B. B. (2009). Bats aloft: Variability in echolocation call structure at high altitudes. Behavioral Ecology and Sociobiology, 64(1), 69-79. https://doi.org/10.1007/s00265-009-0819-1
Kunz, T. H.; Robson, S. K. (1995). Postnatal Growth and Development in the Mexican Free-Tailed Bat (Tadarida brasiliensis mexicana): Birth Size, Growth Rates, and Age Estimation. Journal of Mammalogy. 76 (3): 769. https://doi.org/10.2307/1382746
Marks, C. S. and G. E. Marks. (2006). Bats of Florida. University Press of Florida. Gainesville, Fl. 176 pp.
McCracken, G. F., Safi, K., Kunz, T. H., Dechmann, D. K., Swartz, S. M., & Wikelski, M. (2016). Airplane tracking documents the fastest flight speeds recorded for bats. Royal Society open science, 3(11), 160398. https://doi.org/10.1098/rsos.160398
McWilliams, L. A. (2005). Variation in Diet of the Mexican Free-Tailed Bat (Tadarida brasiliensis mexicana), Journal of Mammalogy, 86(3), 599–605. https://doi.org/10.1644/1545-1542(2005)86[599:VIDOTM]2.0.CO;2
Weigl, R. (2005). Longevity of mammals in captivity; from the living collections of the world. Stuttgart, Germany: Kleine Senckenberg-Reihe.
Wilkins, K. (1989). Tadarida brasiliensis. Mammalian Species (331): 1–10. https://doi.org/10.2307/3504148
Williams, T. C., Ireland, L. C., & Williams, J. M. (1973). High Altitude Flights of the Free-Tailed Bat, Tadarida brasiliensis, Observed with Radar. Journal of Mammalogy, 54(4), 807–821. https://doi.org/10.2307/1379076