Mexican Free-tailed Bat

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A Mexican free-tailed bat living in the Van Horn Maintenance Shop of the Texas Department of Transportation.

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Chiroptera
Family:	Molossidae
Genus:	Tadarida
Species:	T. brasiliensis

Binomial name

Tadarida brasiliensis
(I. Geoffroy, 1824)

The Mexican Free-tailed Bat (Tadarida brasiliensis) is a medium sized bat. Their bodies are about 9 cm (3.5 in) in length, and they weigh about 15 g (0.5 oz). Their ears are wide and set apart to help them find prey with echolocation. The fur color varies from dark brown to gray.

The Mexican Free-tailed Bat is widely regarded as one of the most abundant mammals in North America and is not on any federal lists. However, its proclivity towards roosting in large numbers in relatively few roosts makes it especially vulnerable to human disturbance and habitat destruction. Documented declines at some roosts are cause for concern. It is considered a Species of Special Concern due to declining populations and limited distribution in Utah. The whereabouts and status of winter populations of these animals is still largely unknown.^[1]

Mexican Free-tailed Bats live in caves in the western and southern United States, Mexico, Central America, the West Indies, central Chile and Argentina. Their colonies are the largest congregations of mammals in the world. The largest colony is found at Bracken Cave, north of San Antonio, Texas, with nearly 20 million bats; research indicates that bats from this colony congregate in huge numbers at altitudes between 600 and 3,200 ft (180-1000 m), and even as high as 10,000 ft (3000 m). It is believed that these bats are feeding on migrating cotton bollworm moths, a severe agricultural pest.^[2]

When the baby bats are born, their mothers leave them behind in the cave while they go out to hunt insects. She remembers where she left her "pup" by recognizing its unique "cry" and smell.

The species is very important for the control of pest-insect populations. But its populations are in an alarming decline because of the pesticide poisoning and the destruction of their roosting caves. A population decline in Eagle Creek Cave was documented from over 25 million in 1963 to just 30,000 six years later, and the famous Carlsbad Caverns population, estimated to contain 8.7 million in 1936, had fallen as low as 218,000 by 1973. In addition, the bats lose roosting habitat as old buildings are destroyed. Human disturbance and vandalism of key roosting sites in caves are likely the single most serious causes of decline. Grossly exaggerated media stories about rabies have led to the intentional destruction of large colonies.

One of the most cost-effective ways to help this highly beneficial bat is through key roost protection, public education, and provision of "bat-friendly" bridge designs and other artificial roosts.

In Austin, Texas, a colony of Mexican Free-tailed bats summers (they winter in Mexico) under the Congress Avenue Bridge ten blocks south of the state capitol. It is the largest urban colony in North America with an estimated 1,500,000 bats.^[3] Each night they eat 10,000 to 30,000 pounds of insects. Each year they attract 100,000 tourists who come to watch them. In Houston, Texas, there is a colony 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.^[4]

One of the largest Mexican Free-tailed bat populations inhabits, during the spring and summer, Cueva de la Boca, a cave near Monterrey, Mexico. In 2006, the Mexican environmental conservation NGO, Pronatura Noreste purchased the property. Due to a reduction of more than 95% of the original 20 million bat individuals population, as a result of vandalism, pollution, and uncontrolled tourism, the organization decided to buy the property in order to place it under conservation. Other species of high ecological value that inhabit the cavern are also being protected.