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Tadarida brasiliensisBrazilian free-tailed bat

By Jessica Sosnicki

Geographic Range

Tadarida brasiliensis is a member of one of the widely distributed genera of bats in North and South America. Extensive studies on their range have yet to be completed, especially within South America; however they have been found throughout the much of the United States, Mexico, Central America, and southwestern South America, including Brazil, Chile, and Argentina. In the United States Tadarida brasiliensis is found from southern Oregon to Nevada and eastward to North Carolina and southwestern Virginia. In the last 50 to 100 years, Tadarida brasiliensis populations have declined, possibly due to a decrease in habitat, damage to roosts, and indirect consumption of pesticides. (Cranford and Fortune, 1994; Gannon, et al., 2005; Wilkins, 1989)

Habitat

Brazilian free-tailed bats use a variety of different roost sites, including caves and man-made structures, such as bridges and attics. Caves with large rooms and high ceilings are the primary roosting habitats, although roosts also occur in hollow trees. Roosts are used for nesting, breeding, and interaction between individuals. (Wilkins, 1989)

Physical Description

With brown fur and large ears, Brazilian free-tailed bats are medium-sized, with distinctive short snouts and wrinkled upper lips. The free-tailed bats, which include the genera Tadarida, Eumops, and Nycintomops, are most easily recognized by their “free-tail,” which extends well beyond the uropatagium. They have powerful legs and can climb well. Their long, narrow, pointed wings make them well-suited for rapid, direct flight. Like other temperate bat species, Brazilian free-tailed bats take advantage of daily torpor to conserve energy and may hibernate. (Gannon, et al., 2005; Jones Jr. and Manning, 1992; Wilkins, 1989)

Adults range in size from 79 to 98 mm in length, with a tail almost half the size (31 to 41 mm). Their body mass varies seasonally and depending on maturity, adults typically weigh 7 to 12 g. Ear length is 8 to 15 mm, forearm length ranges from 37 to 41 mm, and their hindfoot measures 6 to 9 mm. The dental formula is the same as other members of the genus Tadarida: Incisors= 1/3, canines= 1/1, premolars= 2/2, molars= 3/3, with a total of 32 teeth. (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

Reproduction

Male Brazilian free-tailed bat behavior and scent-marking changes throughout the year based on the breeding season. Females gather in large numbers at maternity roosts in caves, while smaller groups can be found in tree, bridges, buildings, and other man-made structures. Males vocalize and mark territories in order to attract potential mates. Male and female free-tailed bats call to each other, singling out a mate. Once found, they move away from the group. Males aggressively mate with the female, restricting her movement by grabbing her neck, jaw, or ear. He moves onto her back, biting her neck to keep her in place. The female and male call to each other during mating. Some free-tailed bats mate multiple times, moving from mate to mate. (Gannon, et al., 2005; Keeley and Keeley, 2004; Krutzsch, et al., 2002; Wilkins, 1989)

Brazilian free-tailed bat males mature at about two years, while females mature at nine months. They are monestrous, with females having one annual estrous cycle lasting roughly five weeks during ovulation, which occurs in the spring. Male sexual activity coincides with spring female receptivity, suitable timing for mating interactions to occur. Females usually give birth to a single offspring after an 11 to 12 week gestation period. Births occur upside down and last roughly 90 seconds. It takes an additional 10 to 15 minutes for the newborn to find a nipple for feeding. The sex-ratio is typically 1:1 in pups. (Gannon, et al., 2005; Krutzsch, et al., 2002; Wilkins, 1989; de Magalhaes and Costa, 2009)

  • Breeding interval
    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

Because mothers do not roost with their offspring, but rather leave them with a larger cluster of pups (a creche), she has to identify her own young through a series of calls and odors produced by the pup. Loughry and McCracken (1991) found that the scent of mothers is imprinted during early stages of development; however, pups will try latching onto any female that passes in the cluster to get fed. The young are nursed daily. They reach adult size, are weaned, and are independent in 4 to 7 weeks after birth. Brazilian free-tailed bat females have the highest milk fat content of any bat, over 28% fat, which allows their pups to grow relatively 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

Lifespan/Longevity

Dental studies determined that the longest-living individual was over eight years old. Most adults have a survival rate of 70 to 80% each year, with the rate decreasing with age. Males and females have roughly equal lifespan and mortality rates. The longest reported life in captivity was 12 years old, so it is expected that they can live longer than 12 years in captivity. (de Magalhaes and Costa, 2009; Gannon, et al., 2005; Weigl, 2005; Wilkins, 1989; de Magalhaes and Costa, 2009)

Behavior

Brazilian free-tailed bats start foraging after sunset and feed through the night. They may fly over 50 kilometers to get to a foraging area. Their flight is quick and straight. At over 3300 meters, this species has the highest recorded flight altitude among bats. Brazilian free-tailed bats are also capable of long-distance flight, allowing them to forage over large areas and migrate seasonally. (Allen, et al., 2009; Svoboda and Choate, 1987; Williams, et al., 1973)

Observations in a Colorado mine documented that Brazilian free-tailed bats were most active, through feeding and searching for roost sites, in the late morning and afternoon during the months of June through September. Weather can affect their activity; warm weather stimulates greater activity and there is less activity in cold weather. During their waking hours, Brazilian free-tailed bats call, squeak, and move around. They are social animals that live in large colonies. (Allen, et al., 2009; Svoboda and Choate, 1987; Williams, et al., 1973)

Home Range

Radar studies have tracked this species, and estimate large groups to cover areas of 400 square km and reach altitudes of 3300 m. With a range this size, it is not surprising that this species will travel 25 km to forage in an evening. Indeed, records report travels up up to 65 km from roosts. (Williams, et al., 1973)

Communication and Perception

Brazilian free-tailed bats use echolocation as their primary mode of perception for navigation and detecting prey. They emit brief constant frequency calls as they travel, unless food or another object is detected, then they transfer to modulated frequency calls between 75 and 40 kHz. Their normal frequency ranges from 49 to 70 kHz, but can drop to 25 to 40 kHz when objects cross their flight path. Mate and intra-specific recognition is determined through the use of echolocation and through chemical, visual, and audible vocalizations. Females do not roost with their offspring, they must find their young through scent and sound recognition. (Gannon, et al., 2005; Gillam and McCracken, 2007)

Food Habits

Brazilian free-tailed bats are aerial insectivores that use echolocation to find and consume their prey. Their diet varies based on geographical range, but mainly includes moths (Lepidoptera), beetles (Coleoptera), dragonflies (Odonata),flies (Diptera), true bugs (Hemiptera), and wasps, bees, and ants (Hymenoptera). Diet is influenced by the abundance of prey, weather conditions, metabolic demands, and lunar illumination, which can alter food availability. Brazilian free-tailed bats prey on flying insects while they are, themselves, in flight. (McWilliams, 2005)

  • Animal Foods
  • insects

Predation

Predators of Brazilian free-tailed bats include a number of raptors, such as red-tailed hawks (Buteo jamaicensis), American kestrels (Falco sparverius), great horned owls (Bubo virginianus), barn owls (Tyto alba), and Mississippi kites (Ictinia mississippiensis). Virginia opossums (Didelphis virginiana), striped skunks (Mephitis mephitis), and raccoons (Procyon lotor are among the mammalian roost predators. Snakes also prey on these bats in roosts, including eastern coachwhips (Masticophis flagellum) and eastern coral snakes (Micrurus fulviusprey). However, predation on Tadarida brasiliensis is rare; the number of bats lost due to predation is very low compared to their total population of around 100 million individuals. ("Brazilian Free-tailed Bat", 1997; Davis, et al., 1962; Wilkins, 1989)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Brazilian free-tailed bats are also known as guano bats. Excrement (guano) in roosts can build-up and result in tons of guano. Guano can be harvested as fertilizer and can pose a health risk in spreading diseases that are transmitted through the air (e.g., histoplasmosis). During the summer, disease transmission risk worsens, with higher temperatures and movement from within the caves generating dust clouds. Higher temperatures are also ideal for parasites and pathogens. (Davis and Loomis, 1971; Davis, et al., 1962; Jameson, 1959; Wilkins, 1989)

Brazilian free-tailed bats play host to both ecto- and endoparasites. Individuals that are part of a colony are at higher risk for being parasitized than individuals in smaller roosts. Mite, tick, chigger, flea, and beetle infections are common among Brazilian free-tailed bats, and may act as vectors for other diseases. For example, the chigger Microtrombicula merrihewi affects the nasal passages of Brazilian free-tailed bats, while other parasites affect the blood stream and digestive system. Brazilian free-tailed bats, like other mammals, are also hosts for the rabies virus and at least five other known viruses, such as the 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)

During the summer months, these bats significantly affect local insect populations, which makes maintaining them important to agriculture and human health by eating agricultural pests and disease vectors. More studies are needed on associations with other bat species. In Texas, Myotis velifer are most commonly seen in roosts with T. brasiliensis. Although segregated, individuals can be seen within the other’s colony especially if the roost is crowded. The flight paths of M. velifer and T. brasiliensis differ, which helps avoid competition between the two species while exiting the roost. Roosts of Brazilian free-tailed bats are used by deer mice (Peromyscus species) and squirrels. (Davis and Loomis, 1971; Davis, et al., 1962; Jameson, 1959; Wilkins, 1989)

Commensal/Parasitic Species
  • chiggers (Microtrombicula merrihewi)
  • ticks (Ixodoidea)
  • chiggers (Trombiculidae)
  • fleas (Siphonaptera)
  • beetles (Coleoptera)

Economic Importance for Humans: Positive

Brazilian free-tailed bats eat large numbers of insects nightly, some of which are agricultural pests or disease vectors. Their positive economic impact on agriculture is substantial. However, agricultural pests are often exposed to pesticides through agricultural applications, which can indirectly lead to population decline. In addition, the large amount of guano produced in Brazilian free-tailed bat colonies are used for fertilizer and as a component in gunpowder. (Clark Jr., et al., 1996; Davis, et al., 1962)

  • Positive Impacts
  • produces fertilizer
  • controls pest population

Economic Importance for Humans: Negative

There is no known negative economic importance. However, histoplasmosis is a potential health concern in caves with large guano accumulations and, like other bats, Brazilian free-tailed bats can carry and transmit rabies. (Gannon, et al., 2005)

Conservation Status

Populations of Tadarida brasiliensis have declined over the last century. Some suggest this decline has been caused by disturbance and destruction of roost sites and indirect poisoning by pesticides. Tadarida brasiliensis is labeled as “near threatened” by the International Union for Conservation of Nature, with a Species Action Plan created. (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.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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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