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Brazilian free-tailed bat

Tadarida brasiliensis

What do they look like?

Brazilian free-tailed bats are medium-sized bats with brown fur and big ears. They have short noses and wrinkly upper lips. Like other free-tailed bats, their tail goes past the skin that stretches up to it from their wings. They have strong legs and are good at climbing. Their wings are long, narrow, and pointed. This makes their bodies specially designed for quick, direct flights. Like other North American bats, they lower their body temperature and energy use every day by deeply resting. This is called torpor, which is a kind of hibernating. (Gannon, et al., 2005; Jones Jr. and Manning, 1992; Wilkins, 1989)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    7 to 12 g
    0.25 to 0.42 oz
  • Range length
    79 to 98 mm
    3.11 to 3.86 in
  • Average wingspan
    280 mm
    11.02 in
  • Range basal metabolic rate
    1.99 to 7.31 cm3.O2/g/hr

Where do they live?

Brazilian free-tailed bats are found throughout North and South America. They are found in large parts of the United States, and also in Mexico, Central America, Brazil, Chile, and Argentina. In the United States, they are found from southern Oregon to Nevada, east to North Carolina and southwestern Virginia. In the last 50 to 100 years, their numbers have declined, possibly because of habitat loss, damage to resting locations, and pesticides. (Cranford and Fortune, 1994; Gannon, et al., 2005; Wilkins, 1989)

What kind of habitat do they need?

Brazilian free-tailed bats are found in different environments like caves as well as structures built by people like bridges and attics. They are most often found in caves that have large rooms and high ceilings, but also roost in hollow trees. They roost in these locations, which is when they hang upside down to rest or sleep. In these roosting locations, they nest, breed, and interact with each other. (Wilkins, 1989)

How do they reproduce?

Male Brazilian free-tailed bats have different behaviors during the breeding season. Females gather together in maternity groups, which have both female bats and their young. Maternity groups in caves are large, and maternity groups in structures built by humans like bridges and buildings are smaller. Males make noise and mark territories to attract mates. Males and females call to each other, and single each other out. Once they are paired, they move away from the group. Males and females can have more than one mate. (Gannon, et al., 2005; Keeley and Keeley, 2004; Krutzsch, et al., 2002; Wilkins, 1989)

Brazilian free-tailed bats breed once a year. They mate in the spring, and then the pups grow inside the females for 11 to 12 weeks. Females usually have one pup per year. They give birth upside down, which takes about 90 seconds. Then, it takes the newborn bats 10 to 15 minutes to find their mother's milk. In a group of Brazilian free-tailed bats, the number of males and females in about the same. After nine months, females are grown up. After two years, males are grown up. (Gannon, et al., 2005; Krutzsch, et al., 2002; Wilkins, 1989; de Magalhaes and Costa, 2009)

  • How often does reproduction occur?
    Breeding occurs once yearly.
  • Breeding season
    Ovaluation lasts roughly 5 weeks in females and occurs in spring, when breeding occurs.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    11 to 12 weeks
  • Range time to independence
    4 to 7 weeks
  • Average age at sexual or reproductive maturity (female)
    9 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    273 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    2 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    547 days
    AnAge

Mothers leave their pups in a large group, so they have to use smells and calls to tell which ones are their young. Young Brazilian free-tailed bats can pick out their mother's scent, but they will try to get fed by any females in the group. The young get milk from their mothers every day. They are able to eat other foods after they reach adult size. After 4 to 7 weeks, they are independent of their parents. Their milk is 28% fat, which is the highest fat content of any bat. This helps their pups to grow fairly quickly. (Gannon, et al., 2005; Kunz and Robson, 1995; Loughry and McCracken, 1991; Wilkins, 1989)

  • Parental Investment
  • altricial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

How long do they live?

The record for the longest life of a Brazilian free-tailed bat in the wild is over 8 years old. About 70 to 80% of adults survive each year. The longest reported life in captivity was 12 years. (Gannon, et al., 2005; Weigl, 2005; Wilkins, 1989; de Magalhaes and Costa, 2009)

How do they behave?

Brazilian free-tailed bats are social animals that live in large groups called colonies that call, squeak, and move around. They start searching for food right after sunset and keep going throughout the night. They may fly 50 km or father to get to a feeding area. They fly quickly in a straight line. They fly at a higher altitude than other kind of bats, going up to 3300 m. They can fly a long ways, which means they can find food in a large area and travel between summer and winter locations. The most active they get during the day is feeding and searching for places to rest, which happens in the late morning and afternoon during the summer and early fall. They are more active in warm weather. (Allen, et al., 2009; Svoboda and Choate, 1987; Williams, et al., 1973)

Home Range

Brazilian bats can search for food in an area up to 400 square km. In just one night, they might travel 25 km searching for food, or even as many as 65 km. (Williams, et al., 1973)

How do they communicate with each other?

Brazilian free-tailed bats navigate and find prey by echolocation, which is a way of judging distance by listening to echoes. While flying, they send out calls with constant frequency. When they pick up on food or another object, their calls change frequency to between 75 and 40 kHz. Their normal frequency is 49 to 70 kHz, but can drop to 25 to 40 kHz when objects cross their flying path. Brazilian free-tailed bats recognize each other using echolocation and also chemical signals, sight, and hearing. Females find their young by scent and recognizing the sounds they make. (Gannon, et al., 2005; Gillam and McCracken, 2007)

What do they eat?

Brazilian free-tailed bats eat insects out of the air while they are still flying. They eat different things in different areas, but mostly eat moths, beetles, dragonflies, flies, true bugs, and wasps, bees, and ants. What they eat depends on what is available, the weather, their body's energy use. How bright the moon is can also affect which insects are available to eat. (McWilliams, 2005)

  • Animal Foods
  • insects

What eats them and how do they avoid being eaten?

Brazilian free-tailed bats are eaten by birds of prey like red-tailed hawks, American kestrels, great horned owls, barn owls, and Mississippi kites. Virginia opossums, striped skunks, and raccoons are all mammals that eat them when they are resting. They are also eaten by snakes like eastern coachwhips and eastern coral snakes. Despite all these predators, not very many Brazilian free-tailed bats end up being eaten compared to how many there are. ("Brazilian Free-tailed Bat", 1997; Davis, et al., 1962)

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

Brazilian free-tailed bats are also known as guano bats. Guano is the name for the body waste that builds up on the ground, and can be used for fertilizer. It also can transmit diseases, and increase parasites during warm summer months. The bats are more likely to get parasites if they live in a colony. They get mites, ticks, chiggers, fleas, and beetles. These parasites can transmit other diseases, too. Some chiggers infect their nose, and others get in their blood or digestive system. Like other mammals, Brazilian free-tailed bats carry rabies and five other viruses. These are: Rio Bravo virus, St. Louis encephalitis virus, Eastern equine encephalitis, Western equine encephalitis, and Japanese B encephalitis. (Davis and Loomis, 1971; Davis, et al., 1962; Jameson, 1959; Wilkins, 1989)

Brazilian free-tailed bats decrease the number of insects during the summer. Their resting locations are sometimes used by deer mice or squirrels. They also share resting spots with cave myotis, and can even be found inside one another's colonies if it gets crowded. They fly on different paths out of the cave, so they don't get in each other's way. (Davis and Loomis, 1971; Davis, et al., 1962; Jameson, 1959; Wilkins, 1989)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • chiggers (Microtrombicula merrihewi)
  • ticks (Ixodoidea)
  • chiggers (Trombiculidae)
  • fleas (Siphonaptera)
  • beetles (Coleoptera)

Do they cause problems?

Brazilian free-tailed bats aren't known to have a negative impact on humans. On the other hand, their guano might transmit the disease histoplasmosis. They can also carry rabies, which is deadly to humans. (Gannon, et al., 2005)

How do they interact with us?

Brazilian free-tailed bats eat lots of insects every night, including some that are pests to farmers or others that carry disease. The build-up from their body waste, called guano, is used as fertilizer and also used in gunpowder. (Clark Jr., et al., 1996; Davis, et al., 1962)

  • Ways that people benefit from these animals:
  • produces fertilizer
  • controls pest population

Are they endangered?

The number of Brazilian free-tailed bats has decreased in the past 100 years. This might be from disturbing their daytime locations or from being poisoned by pesticides. Brazilian free-tailed bats are listed as "Near Threatened" by the IUCN Red List. They have created a species action plan for conservation. (Arita, 1993; Gannon, et al., 2005)

Contributors

Jessica Sosnicki (author), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.

References

1997. "Brazilian Free-tailed Bat" (On-line). The Mammals of Texas - Online Edition. Accessed April 06, 2010 at http://www.nsrl.ttu.edu/tmot1/tadabras.htm.

Allen, L., A. Turmelle, M. Mendonca, K. Navara, T. Kunz, G. McCracken. 2009. Roosting ecology and variation in adaptive and innate immune system function in the Brazilian free-tailed bat (Tadarida brasiliensis). Journal of Comparative Physiology, 179: 315–323.

Arita, H. 1993. Conservation Biology of the Cave Bats of Mexico. Journal of Mammalogy, 74/3: 693-702.

Clark Jr., D., A. Lollar, D. Cowman. 1996. Dead and dying Brazilian free-tailed bats (Tadarida brasiliensis) from Texas: rabies and pesticide exposure. The Southwestern Naturalist, 41/3: 275-278.

Cranford, J., D. Fortune. 1994. Mexican free-tailed bats at Mt. Lake Biological Station.. Virginia Journal of Science, 45/2: 111.

Davis, R., C. Herreid, H. Short. 1962. Mexican Free-Tailed Bats in Texas. Ecological Monographs, 32/4: 311-346.

Davis, R., R. Loomis. 1971. The Intranasal Chigger Mircotrombicula merrihewi (Acarina: Trombiculidae) in the North American Free-Tailed Bat, Tadarida brasiliensis.. The Southwestern Naturalist, 15/4: 437-458.

Gannon, M., A. Kurta, A. Rodriquez-Duran, M. Willig. 2005. Bats of Puerto Rico. Jamaica: The University of the West Indies Press.

Gillam, E., G. McCracken. 2007. Variability in the echolocation of Tadarida brasiliensis: effects. Animal Behavior, 74: 277-286.

Humphrey, S. 1971. Photographic estimation of population size of the Mexican free-tailed bat, Tadarida brasiliensis. American Midland Naturalist, 86/1: 220-223.

Jameson, D. 1959. A Survey of the Parasites of Five Species of Bats. The Southwestern Naturalist, 4/2: 61-65.

Jones Jr., J., R. Manning. 1992. Illustrated Key to Skulls of Genera of North American Land Mammals. Lubbock, Texas: Texas Tech University Press.

Keeley, A., B. Keeley. 2004. The Mating System of Tadarida brasiliensis (Chiroptera: Molossidae) in a Large Highway Bridge Colony. Journal of Mammalogy, 85/1: 113-1. Accessed April 06, 2010 at http://www.bioone.org/doi/abs/10.1644/BME-004.

Krutzsch, P. 1955. Observations on the Mexican free-tailed bat, Tadarida mexicana. Journal of Mammalogy, 36/2: 236-242.

Krutzsch, P., T. Fleming, E. Crichton. 2002. Reproductive biology of male Mexican free-tailed bats (Tadarida brasiliensis mexicana). Journal of Mammalogy, 83/2: 489-500.

Kunz, T., S. Robson. 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: 769-783.

Lee, Y., G. McCracken. 2001. Timing and variation in the emergence and return of Mexican free-tailed bats (Tadarida brasiliensis mexicana). Zoological Studies, 40/4: 309-316.

Loughry, W., G. McCracken. 1991. Factors influencing female-pup scent recognition in Mexican free-tailed bats. Journal of Mammalogy, 72/3: 624-626.

McWilliams, L. 2005. Variation in diet of the Mexican free-tailed bat (Tadarida brasiliensis mexicana). Journal of Mammalogy, 86/3: 599-605.

Reichard, J., L. Gonzalez, C. Casey, L. Allen, N. Hristov, T. Kunz. 2009. Evening emergence behavior and seasonal dynamics in large colonies of Brazilian free-tailed bats. Journal of Mammalogy, 90/6: 1478–1486.

Russell, A., R. Medellin, G. McCracken. 2005. Genetic variation and migration in the Mexican free-tailed bat (Tadarida brasiliensis mexicana). Molecular Ecology, 14: 2207–2222.

Schmidly, D. 1994. The Mammals of Texas. Austin, TX: University of Texas Press.

Svoboda, P., J. Choate. 1987. Natural history of the Brazilian free-tailed bat in the San Luis Valley of Colorado. Journal of Mammalogy, 68/2: 224-234.

Weigl, R. 2005. Longevity of mammals in captivity; from the living collections of the world. Stuttgart, Germany: Kleine Senckenberg-Reihe.

Wilkins, K. 1989. Mammalian Species: Tadarida brasiliensis. Mammalian Species, 331: 1-10.

Williams, T., L. Ireland, J. Williams. 1973. High altitude flights of the free-tailed bat, Tadarida brasiliensis, observed with radar. Journal of Mammalogy, 54/4: 807-821.

de Magalhaes, J., J. Costa. 2009. "AnAge entry for Tadarida brasiliensis" (On-line). AnAge: The Animal Ageing and Longevity Database. Accessed April 06, 2010 at http://genomics.senescence.info/species/entry.php?species=Tadarida_brasiliensis.

 
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Sosnicki, J. 2012. "Tadarida brasiliensis" (On-line), Animal Diversity Web. Accessed December 18, 2014 at http://www.biokids.umich.edu/accounts/Tadarida_brasiliensis/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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