Millions of Brazilian free-tailed bats spend their summers in the southwestern United States. Gigantic colonies summer in Bracken Cave, Texas; Carlsbad Caverns, New Mexico; and even within the city of Austin, Texas, under the Congress Avenue Bridge. They are a spectacular sight spiraling out of their day roosts like great, dark, swirling clouds when they emerge in the evening to forage. The bats eat untold numbers of insects each night, sometimes catching their prey at altitudes of a mile or more. They typically migrate to central and southern Mexico in the winter, where they live in smaller colonies. They mate there, and fly north again - as far as 1,300 km - between February and April. Females give birth to a single pup, in June, and nurse it for about six weeks. Although they number in the millions, conservation is a concern, because they raise their young in a limited number of caves, and because pesticides can accumulate in their body tissues.

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A particularly well-studied species, the Brazilian free-tailed bat exhibits some spectacular behaviour. It forms the largest warm-blooded colonies in the world, emerging to feed at dusk in huge columns of several million individuals. Their flapping wings create a sound equivalent to a white-water river and their numbers are great enough to be detected by airport and weather radars (7). Feeding for longer each night than any other bat species, it travels as far as 31 miles from the roost to the feeding grounds and uses echolocation to find its prey. The Brazilian free-tailed bat flies at up to 47 mile per hour in open spaces, foraging with fast, straight flight (6). Each bat consumes between 200 and 600 insects a night, selecting mainly moths, but also eating beetles, flying ants and leafhoppers (3). The Brazilian free-tailed bats of Texas are estimated to consume from 6,000 to 18,000 metric tons of insects each year, many of which are agricultural pests (2). At dawn, they return to their roosts where they swarm before re-entering. Thought to be a predator-avoidance tactic, the bats gather into groups at a great height above the cave, before closing their wings and dropping rapidly in one continuous stream. Predators waiting at the mouth of the cave to catch emerging bats include red-tailed hawks, owls, raccoons, opossums, skunks and snakes (7). Mating takes place in March and shortly afterwards the females migrate to female-only maternity roosts. Most adult males do not leave the tropical and subtropical part of the range and therefore contribute nothing to rearing the young. Gestation lasts for 90 days (2) and females give birth within around 15 days of each other to a single young, known as a pup (7). The female clings to the roost with both thumbs and one or both feet to give birth, and remains attached to the pup via the umbilical cord for up to an hour while she cleans and nurses her offspring. In the first hour the young bat learns to cling to the roost wall and other bats with its hands, feet and teeth. Once stable, the female pulls away from the pup, dislodging the placenta, which hangs from the pup until it dries out and falls off several days later. During this time the number of bats in the roost doubles, and a female must locate her own pup by listening for its calls. She may land several times, eventually finding her pup by scent. Once reunited she touches the top of its head with her muzzle to confirm the bond (7). A consequence of the enormous number of bats in a single cave is the build up of guano, or bat droppings. This nutrient-rich mixture was once commercially extracted from caves on a large scale, to be sold as fertiliser. In the early 1900s it was the largest mineral export from Texas after oil, and it continues to be sold commercially although to a lesser degree. Bat caves are widely known to contain noxious gases, but this is actually a result of carpet beetles (Dermestidae) that feed on guano and fallen bats. These beetles multiply so rapidly as a result of such a constant food supply that the whole floor of a cave may be 'carpeted' with them, hence their common name. They produce waste that combines with water vapour to make ammonium hydroxide which is poisonous to most animals. Bats have adapted to this potent atmosphere by lowering their metabolic rate, which causes the level of carbon dioxide dissolved in their blood to rise, thus neutralising the ammonia. Their fur, however, may become bleached to a reddish-brown colour. The first flight of the five-week-old bats is fraught with danger as they become used to their wings and echolocation system. Collisions, failed flights, and unsteady landings can result in bats falling to the cave floor, where they are stripped to the bone in minutes by the beetles (7).

A member of the Molossidae family, the Brazilian free-tailed bat has the characteristic mouse-like tail protruding beyond the flight membrane stretched between its hind legs. Relatively plain when compared to many bats, this species has brown fur, large ears that are nearly square, and a strongly wrinkled upper lip. However, it is superbly adapted to its aerial lifestyle, having long, narrow wings with pointed tips to enable very fast flight, and long hairs on the toes to judge flight speed and turbulence. The hind legs are short and powerful, making this bat an excellent climber (3).

This species is found from southern Brazil, Bolivia, Argentina, and Chile to Oregon, southern Nebraska and Ohio (USA); Greater and Lesser Antilles (Simmons 2005). Distribution extended to Falkland Islands. Not found in Nicaragua (Medina pers. comm.)

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.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Southern Oregon, northern Nebraska, and southern North Carolina (some records farther north) southward through most of Central America and Antilles (south to St. Lucia in Lesser Antilles; Tobago record probably an accidental, Jones 1989) to central Argentina, southern Brazil, and central Chile, excluding Amazonia (Wilkins 1989, Honacki et al. 1982).

Despite its name, the Brazilian free-tailed bat is actually widespread throughout South, Central and North America. It has fairly complex migratory habits; some populations travel from the extreme north of the range to the extreme south, whilst others remain resident year-round. The largest and most well-known populations are found in Mexico and Texas, USA. There are nine subspecies in total; all occupy different ranges and have different migration routes (3). The population is thought to total between 95 and 105 million individuals, with Bracken Cave in Texas holding between 20 and 40 million individuals alone (2). In World War II this species was secretly investigated by the U.S. Air Force for its potential to carry tiny bombs into Japan. Bat caves were carefully guarded but the bats refused to cooperate, instead wreaking havoc in Air Force bases (7).

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.

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.

Range mass: 7 to 12 g.

Range length: 79 to 98 mm.

Average wingspan: 280 mm.

Range basal metabolic rate: 1.99 to 7.31 cm^3 oxygen/hour.

Other Physical Features: endothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

Length: 11 cm

Weight: 14 grams

Sexual Dimorphism: Males may be about 5% longer than females but females weigh about 5% more than males.

Length:
Average: 95 mm
Range: 85-109 mm

Weight:
Range: 10-15 g

Habitat and Ecology

Systems

• Terrestrial

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.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: chaparral ; forest

Other Habitat Features: urban ; suburban ; caves

Comments: Roosts primarily in buildings (generally old ones) in southeastern U.S. (sometimes in hollow trees), U.S. West Coast, and Jamaica; in caves in southwestern U.S.; in both buildings and caves in Puerto Rico. May use rock crevice, bridge, sign, or cliff swallow nest as roost during migration. Generally roosts high (at least 3 m) above ground to allow free fall required to attain flight. Large maternity colonies inhabit buildings and caves (rarely used in Florida); also uses culverts and bridges. Tends to return to natal cave to breed (Caire et al. 1989).

The Brazilian free-tailed bat is found in many different habitats from desert through pinion-juniper woodland to pine-oak forests. It inhabits areas from sea level to 3,000 metres, and roosts in limestone caves, abandoned mines, under bridges, in buildings and in hollow trees (5).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

In the eastern U.S. (to eastern Texas) and U.S. West Coast: hibernates but does not migrate. Antillean subspecies ANTILLARUM does not migrate (Jones 1989). Texas and Great Plains through southwestern U.S.: most migrate to Mexico or to southwestern U.S., usually toward end of October, return in March. (See Wilkins 1989 for more detail.) Individuals from southern Great Plains migrate, beginning in late August, to winter range from southern edge of Edwards Plateau in Texas south nearly to latitude of Mexico City (Caire et al. 1989).

Foraging habitat is very broad. May range as far as 80 km from cave to feed (Caire et al. 1989). Bats that roost in Carlsbad Cavern, New Mexico, forage up to at least 56 km from the cavern (Best and Geluso 2003).

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.

Animal Foods: insects

Primary Diet: carnivore (Insectivore )

Comments: Opportunistic; diet includes moths, flying ants, beetles, bugs, and other insects; often preys on densely swarming insects. May fly considerable distances to favorite feeding areas.

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.

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.

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.

Deer mice (Peromyscus species) and squirrels can also be seen using cave roosts as shelters. However, they have no known impact on T. brasiliensis.

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.

Commensal/Parasitic Species:

• chiggers (Microtrombicula merrihewi)
• ticks (Ixodoidea)
• chiggers (Trombiculidae)
• fleas (Siphonaptera)
• beetles (Coleoptera)

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.

Known Predators:

• red-tailed hawks (Buteo jamaicensis)
• American kestrels (Falco sparverius)
• great horned owls (Bubo virginianus)
• barn owls (Tyto alba)
• Mississippi kites (Ictinia mississippiensis)
• Virginia opossums (Didelphis virginiana)
• striped skunks (Mephitis mephitis)
• raccoons (Procyon lotor)
• eastern coachwhips (Masticophis flagellum)
• eastern coral snakes (Micrurus fulviusprey)

Anti-predator Adaptations: cryptic

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: Bulk of total abundance is confined to about 20 caves in the southwestern U.S. Rest are small in size, though numerous. All large colonies probably known.

10,000 to >1,000,000 individuals

Comments: Estimated 120-150 million. See Arita (1993) for information on population size in Mexico.

Roosts in tightly packed groups. Winter congregations typically much smaller than summer colonies. Sexes generally segregate during summer; males may form small (but sometimes up to 100,000) at higher elevations, whereas females usually form nursery colonies in warmer areas of the species' northern range (Freeman and Wunder 1988). Typically feeds within 50-mile radius of day roost, but up to 150 miles away (Whitaker 1980).

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.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; echolocation

Comments: On overcast days, often found feeding in early evening. In predominantly male colony in Colorado: began to leave mine shaft at about 2300 h; a few began returning by 2300, continuing until 0430; none returned after 0515 (Freeman and Wunder 1988); in some areas some groups do not return to cave until after daylight (Caire et al. 1989); in other areas may forage for a few hours, return to cave roost for a few hours, then go out on another foraging trip, returning after dawn. Typically hibernates in the eastern U.S. and on U.S. West Coast.

Dental studies (Gannon et al., 2005) 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. Weigl (2005) reported a live free-tailed bat in captivity that was 12 years old. It is therefore expected that this species can live beyond 12 years in captivity.

Average lifespan

Status: wild: 8 years.

Average lifespan

Status: captivity: 12 years.

Average lifespan

Status: wild: 8.0 years.

Maximum longevity: 12 years (captivity) Observations: In the wild, these animals live at least 8 years (Brunet-Rossinni and Austad 2004). One 12 year old specimen was still alive in captivity (Richard Weigl 2005).

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.

Mating System: monogamous

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.  A female usually gives birth to a single offspring after an 11 to 12 week gestation period. Births occurs 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.

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.

Range gestation period: 11 to 12 weeks.

Average birth mass: 2.8 g.

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 (male): 2 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average birth mass: 2.8 g.

Average number of offspring: 1.

Average age at sexual or reproductive maturity (male)

Sex: male: 547 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 273 days.

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.

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)

Breeds late February-March or early April in North America. None of 8 females collected in late December in Jamaica was pregnant (Goodwin 1970). Gestation lasts 2.5-3.5 months. Births mainly June-July in North America (early to mid-June in Texas). Litter size: 1 (females occasionally carry 2 embryos). Despite the huge numbers of young that may be present in a colony, females recognize and nurse their own offspring. Young nurse for about 45 days, first fly at 6-7 weeks. Females may become pregnant as yearlings; males become sexually mature at 18-22 months. Maternity colonies initially consist of almost only of pregnant females. Some colonies include more than 1 million individuals (20 million adult females give birth in Bracken Cave near San Antonio, Texas); 10,000s in eastern North America. If a nursery falls below about 20,000 females, usually it is abandoned (Caire et al. 1989).

Hot spots cool and heat: Brazilian free-tailed bat
 

The flanks of Brazilian free-tailed bats aid thermoregulation due to a unique arrangement of arteries and veins creating thermal windows.

     
  "The Brazilian free-tailed bat (Tadarida brasiliensis) experiences challenging thermal conditions while roosting in hot caves, flying during warm daylight conditions, and foraging at cool high altitudes. Using thermal infrared cameras, we identified hot spots along the flanks of free-ranging Brazilian free-tailed bats, ventral to the extended wings. These hot spots are absent in syntopic cave myotis (Myotis velifer), a species that forages over relatively short distances, and does not engage in long-distance migration. We hypothesized that the hot spots, or 'radiators,' on Brazilian free-tailed bats may be adaptations for migration, particularly in this long-distance, high-flying species. We examined the vasculature of radiators on Brazilian free-tailed bats with transillumination to characterize the unique arrangements of arteries and veins that are positioned perpendicular to the body in the proximal region of the wing. We hypothesized that these radiators aid in maintaining heat balance by flushing the uninsulated thermal window with warm blood, thereby dissipating heat while bats are flying under warm conditions, but shunting blood away and conserving heat when they are flying in cooler air at high altitudes. We also examined fluid-preserved specimens representing 122 species from 15 of 18 chiropteran families and radiators appeared present only in species in the family Molossidae, including both sedentary and migratory species and subspecies. Thus, the radiator appears to be a unique trait that may facilitate energy balance and water balance during sustained dispersal, foraging, and long-distance migration." (Reichard et al. 2010:358)
  Learn more about this functional adaptation.

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 6 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 6
Species: 32
Species With Barcodes: 1

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.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Reasons: Large range (southern North America to South America); suitable sites for large colonies are extremely limited; threats include pesticides and disturbance to major roosts.

The Brazilian free-tailed bat is classified as Least Concern (LC) on the IUCN Red List (1) and is listed on Appendix I of the Convention on Migratory Species (4).

Near Threatened.

Population

Population Trend

Major Threats

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: Threatened by disturbance, pesticides, and habitat destruction in tropics.

Whilst the Brazilian free-tailed bat exists in extremely large numbers and across a great range of countries and habitat types, it is still classed as a threatened species. This is due to its reliance on a relatively low number of roost sites. With the loss of just one roost site, a large proportion of the population could be destroyed. Some significant declines have been documented, such as the population of Eagle Creek Cave, which fell from 25 million individuals in 1963 to just 30,000 individuals in 1969. These declines are not fully understood, but several threats are present, particularly from the alteration of roost sites and the use of organochlorine pesticides. Insecticides which are found in the bodies of living insects accumulate in the bodies of the bats that eat them in such large numbers, resulting in reduced reproductive success and death (6). Rabies, a disease often associated with bats, is found in members of the Brazilian free-tailed bat population. Humans who attempt to handle bats without the proper precautions have been infected with rabies, which can be fatal. Media sensationalism of this problem has resulted in deliberate eradication attempts and roost destruction (6).

Conservation Actions

Biological Research Needs: A relatively well-studied species. Needs some resolution of subspecies.

Global Protection: Few (1-3) occurrences appropriately protected and managed

Comments: Carlsbad Caverns N.P., New Mexico.

Needs: Protect largest colonies. Protect tropical winter areas.

Although perhaps no species' fate should be judged solely on its importance to humans, the Brazilian free-tailed bat is known to have an enormous impact on insect numbers, thereby contributing to both the ecology and economy of those countries that are home to it. It is crucial to continue to protect its roost sites and to educate the public and the media as to the reality of rabies and the benefits of the Brazilian free-tailed bat (6).

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.

Negative Impacts: causes or carries domestic animal disease

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. Population declines may be linked to toxicity from pesticides.  In addition, the large amount of guano produced in  Brazilian free-tailed bat colonies are used for fertilizer and as a component in gunpowder.

Positive Impacts: produces fertilizer; controls pest population

Comments: Large colonies produce voluminous guano in roost caves; guano has been (and still is) mined for use as a fertilizer in some areas.

Comments: The specific relationships of Antillean populations of Tadarida remain obscure; it has been suggested that Caribbean populations represent a distinct species or that they are related to T. b. cynocephala (of the southeastern U.S.) but not to other populations of the brasiliensis complex (Jones 1989). Two of the nine subspecies (T. b. mexicana and T. b. cynocephala) occur in the U.S. Though morphological data suggest intergradation (Schmidly 1977), these two subspecies differ widely in behavior (migratory vs. nonmigratory) and roost preference, and gene flow between them has been reported to be minimal and unidirectional at most (Owen et al. 1990). However, McCracken and Gassel (1997) found high genetic similarity and evidence of gene flow between these nominal subspecies, such as typically seen between geographic populations of the same subspecies.

The generic name Rhizomops was proposed in 1984 for Tadarida brasiliensis (and presumably all subspecies), but this was rejected by Owen et al. (1990) because the genus was based entirely on plesiomorphic characters.

McCracken et al. (1994) examined allozyme data from several maternity and winter colonies within the range of subspecies mexicana and determined that populations are not structured genetically into distinct geographic units.