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Species of mammal

The Mexican free tailed bat or Brazilian free tailed bat (Tadarida brasiliensis) is a medium sized bat native to the Americas, so named because its tail can be almost half its total length and is not attached to its uropatagium. It has been claimed to have the fastest horizontal speed of any animal, reaching top ground speeds over It also flies the highest among bats, at altitudes around
It is regarded as one of the most abundant mammals in North America. Its proclivity towards roosting in huge numbers at relatively few locations makes it vulnerable to habitat destruction in spite of its abundance. For instance, up to 1.5 million bats reside under just one bridge in Austin. The Texas Legislature designated the Mexican free tailed bat the state mammal (flying) in 1995.

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.

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.

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.