Mexican free-tailed bat

The Mexican free-tailed bat was described as a new species in 1824 by French zoologist Isidore Geoffroy Saint-Hilaire. Geoffroy placed it in the now-defunct genus Nyctinomus with a binomial name of Nyctinomus brasiliensis. The holotype had been collected in Brazil. Molecular sequence data indicate T. brasiliensis's closest relatives are the sister species Sauromys petrophilus of South Africa and Tadarida aegyptiaca of Africa and South Asia. These three species form a clade believed to be about 18 million years old. == Physical description ==

Mexican free-tailed bats are typically in length and weigh around with females tending to be slightly heavier than males by 1–2 grams for increased fat storage to use during gestation and nursing. These bristles, namely those on digits one and five and the toes, as well as on the edge of the uropatagium, are photoluminescent under ultraviolet light. The function of this trait, if any, are unknown. ) The dental formula of Tadarida brasiliensis is . == Range and ecology ==

The Mexican free-tailed bat ranges from the southern half of the continental United States through most of Mexico, and through most of Central America into South America. Their range in South America is less understood where they live in the eastern Brazilian highlands and coast, the northeastern Andes, the coast of Peru and northern Chile, and the center of Argentina. The largest known colony is found at Bracken Cave, north of San Antonio, Texas, with nearly 20 million bats; the bats from this colony congregate in huge numbers at altitudes between , and even as high as . Habitat Mexican free-tailed bats roost primarily in caves. However, they also roost in buildings of any type as long as they have access to openings and dark recesses in ceilings or walls. The bats can make roosting sites of buildings regardless of "age, height, architecture, construction materials, occupancy by humans and compass orientation". and Mexico. Bats ranging eastward from East Texas do not migrate, but local shifts in roost usage often occur seasonally. Large numbers of Mexican free-tailed bats fly hundreds of meters above the ground in Texas to feed on migrating insects. The consumption of insects by these bats can be quite significant. The onset of evening emergence from caves and the end of returns at dawn tend to correlate with sunset and sunrise, respectively, with dawn returns ending increasingly later in correlation to sunrise throughout the summer season. Reproductive females tended to emerge earlier in the evening and return later at dawn to gather the extra nutrients they require for reproduction and offspring care. T. brasiliensis bats spend around 60% of their active time foraging while aerial, mostly hunting at heights of . Health and mortality One individual bat was recorded to have lived eight years, based on dentition. Predators of the bat include large birds such as red-tailed hawk, American kestrels, great horned owls, barn owls, and Mississippi kites. Mammal predators include Virginia opossums, striped skunks, and raccoons. Certain chemicals in the fur of these bats have antimicrobial activity against common mammalian skin pathogens. The chemical nonanal is found in such a concentration that its antimicrobial activity can inhibit the growth of two fungal pathogens that cause ringworm (Trichophyton mentagrophytes and T. rubrum), as well as Malassezia furfur, a yeast. Two other common skin disease-causing microbes that are inhibited by the hair's concentration of nonanal include Staphylococcus aureus and Cutibacterium acnes. == Behavior ==

). Mexican free-tailed bats are nocturnal foragers and begin feeding after dusk. They travel 50 km in a quick, direct flight pattern to feed. This species flies the highest among bats, at altitudes around . Free-tailed bats are more active in warm weather. The species has been measured at a ground speed of , measured by an aircraft tracking device. The measurement methodology did not simultaneously record wind speed and ground speed, so the observations could have been affected by strong local gusts, and the bat's maximum air speed remains uncertain. Guano and ammonia Among bats that roost in great, concentrated numbers, T. brasiliensis roosts produce large quantities of urine and guano; from 22 to 99 metric tons per cave and over 18,700 metric tons are produced annually. The concentrated waste generates high levels of toxic ammonia in the air of a cave. T. brasiliensis individuals have genetic adaptation for withstanding or countering these high levels of ammonia. The bats' content of CO2 and protein in respiratory mucus and CO2 dissolved in blood plasma increase with increasing levels of dissolved ammonia, providing the bats with a buffer against pH change. This allows the bats to filter out a large majority of inhaled ammonia before it reaches toxic levels in the blood. T. brasiliensis bats are thought to swarm in spiraling motions within caves to ventilate ammonia and renew the air. Typically, the frequency range of their echolocation is between 49 and 70 kHz, but can be between 25 and 40 kHz if something crosses their path while in flight. Mating and reproduction During the breeding season, females aggregate into maternity roosts. The size of these roosts depends on the environment, with caves having the larger roosts. Mating can occur in an aggressive or passive form. In the aggressive form, the male controls the female's movements, keeping her away from the other bats in the roost. He also tends to vocalize when mating. During passive copulation, the males simply flies to a female in her roost and quietly mounts her with no resistance. This species is a promiscuous breeder and both sexes copulate with multiple partners. However, young try to steal a suckle from any female that passes through the cluster. Through examining the genotypes of female-pup nursing pairs sampled from colonies in Texas, it has been measured that nursing is partially selective along genetic lines, with approximately 17% of mothers nursing pups that were not their offspring, ostensibly due to the difficulty of consistently locating and selectively nursing their own pups in extremely large colonies. A mother will nurse her young daily, and by 4–7 weeks old they are full grown, fully weaned, and independent. == Conservation ==

Though abundant and widespread, some local populations have prompted protection and conservation efforts. For instance, during the spring and summer, one of the largest Mexican free-tailed bat populations inhabits Cueva de la Boca, a cave near Monterrey, Mexico. In 2006, the Mexican environmental conservation NGO, Pronatura Noreste, purchased the property. Because of a reduction by more than 95% of the original 20 million bat population to 600,000, as a result of vandalism, pollution, and uncontrolled tourism, the organization decided to buy the property to place it under conservation. Other species of high ecological value that inhabit the cavern are also being protected. Similarly, Bat Conservation International bought Bracken Cave from private ownership in 1992. BCI planned to revert any land changes that were a result of farming or ranching in order to conserve the biodiversity and wildlife there. Preserving the land around Bracken Cave was important, as it is home to the world's largest bat colony, and any human encroachment would be detrimental to their population. BCI also protects the land from artificial light pollution, which can distress the bats. Economic importance In Austin, Texas, a colony of Mexican free-tailed bats summers (they winter in Mexico) under the Congress Avenue Bridge 10 blocks south of the Texas State Capitol. It is the largest urban colony in North America, with an estimated 1,500,000 bats. Each night they eat of insects. Each year, they attract 100,000 tourists who come to watch them. In Houston, Texas, a colony is living under the Waugh Street Bridge over Buffalo Bayou. It is the home to 250,000 bats and also attracts viewers. The Mexican free-tailed bat is the official flying mammal of the state of Texas, as well as Oklahoma. Hundreds of tons of guano were mined in Texas annually between 1900 and 1980. In the early 20th century, bat guano was Texas' largest mineral export, before oil. In 1863, a gun powder factory opened near San Antonio, the saltpeter of which was provided by local guano mines. == See also ==