Mexican free-tailed bat

The Mexican free-tailed bat or Brazilian free-tailed bat (Tadarida brasiliensis) is a medium-sized bat native to the Americas, 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. The bat is considered a species of special concern in California as a result of declining populations. It has been claimed to have the fastest horizontal speed (as opposed to stoop diving speed) of any animal, reaching top ground speeds over 160 km/h; its actual air speed has not been measured. The Texas Legislature designated the Mexican free-tailed bat the state mammal (flying) in 1995. 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 6.5 million years old. Mexican free-tailed bats are typically 9 cm (3.5 in) in length and weigh around 7–12 g (0.25–0.42 oz) with females tending to be slightly heavier than males by 1-2 grams for increased fat storage to use during gestation and nursing. Their tails are almost half their total length and stretch beyond the uropatagium, giving them the name 'free-tailed' bats. Their ears are wide, rounded, and large compared to their heads, nearly meeting at the front of the face, but distinctly not joined at the midline and projecting anterodorsally from just before the muzzle to the back of the head. They use their large ears to help them find prey using echolocation. T. brasiliensis is distinguished among North American Tadarida bats in possessing deep wrinkles on the upper lip and in having a Z-shaped upper third molar, which is used for grinding insects. These individuals possess canines which are larger in males than in females. The wings are elongated and narrow with pointed tips, making them well-equipped for quick, straight flight patterns. Their fur color ranges from dark brown to gray. The Mexican free-tailed bat's large feet have distinct long, white bristles.The dental formula of Tadarida brasiliensis is 1.1.1.33.1.2.3. 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, and the coast of Peru and northern Chile. They are absent in much of the Amazon rainforest. They are also found in the Caribbean, and are native to all of the Greater Antilles and 11 of the Lesser Antilles. 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 180 and 1,000 m (590 and 3,280 ft), and even as high as 3,000 m (9,800 ft). 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'. Caves, though, need to have enough wall and ceiling space to fit millions of bats. Before buildings, free-tailed bats in the southeastern United States probably roosted in the hollows of trees such as red mangrove, black mangrove, white mangrove and cypress. However, most bats in Florida seem to prefer buildings and other man-made structures over natural roosts. Caves in Florida tend to be occupied mostly by the southeastern myotis. Caves in Florida tend to have pools of water on the floor and the free-tailed bats do not need as much relative humidity as the southeastern myotis. Mexican free-tailed bats in southeastern Nevada, southwestern Utah, western Arizona, and southeastern California come together to migrate southwest to southern California and Baja California. Bats in southeastern Utah, southwestern Colorado, western New Mexico, and eastern Arizona travel though western edge of the Sierra Madre Oriental into Jalisco, Sinaloa, and Sonora. Some bats that summer in Kansas, Oklahoma, eastern New Mexico, and Texas migrate southward to southern Texas and Mexico. Some bat populations in other areas of North America do not migrate, but are residents and may make seasonal changes in roost sites. While this migration is extremely extensive, a way must exist for these bats to continuously congregate in the same roosts every year. T. brasiliensis bats have copious numbers of sebaceous glands covering their entire bodies. These glands leave a trace of a lasting scent to which other bats are sensitive. This odor is crucial to marking habitual roosts. 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 10,000 to 30,000 lb (4,500 to 13,600 kg) 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. Bats ranging eastward from East Texas do not migrate, but local shifts in roost usage often occur seasonally. Also, a regional population that ranges from Oregon to California, has a year-round residence.