Mexican Free-tailed Bat: Profile and Information

The Mexican free-tailed bat, also referred to as the Brazilian free-tailed bat, is a medium build bat and endemic to the Americas.

It is considered one of North America’s most populated mammals.

Its natural inclination towards roosting in large numbers in a small number of locations makes it very prone to habitat destruction despite its large numbers.

It has been presumed to have the quickest linear speed (in contrast to any animal’s stoop diving speed). It can reach top ground speeds of over 161 kilometers per hour.

Its actual speed in the air has not been measured yet. The Texas Legislature chose the Mexican free-tailed bat as the state mammal (flying) 1995.

The Mexican free-tailed bat covers the southern half of the continental United States through most parts of Mexico and Central America into South America.

Their range in South America covers the eastern Brazilian highlands and coast, the northeastern Andes, the coast of Peru and northern Chile, and Argentina’s center.

They are hardly present in much of the Amazon rainforest. They can be found in the Caribbean and are endemic to all Greater Antilles and 11 of the Lesser Antilles.

The largest known colony of these bats can be found at Bracken Cave, north of San Antonio, Texas, with roughly 20 million bats.

The bats from this colony assemble in massive numbers at altitudes between 590 and 3,280 ft.

In some cases, it is as high as 9,800 ft.

Scientific Classification

Physical Description

The Mexican free-tailed bats have a body length of 9 cm and usually weigh between 7-12 grams.

They are incredibly light animals, but female Mexican free-tailed bats may be slightly heavier than the males by at least a gram for increased fat storage.

This stored fat is used during nursing and gestation.

Their tails are peculiar because they are almost half their entire body length, extending beyond the uropatagium.

For this reason, they were named the free-tailed bats. They possess broad, rounded, and large ears. They are so large that they nearly meet at the front of their faces.

They use their large ears to find prey, employing echolocation. T. brasiliensis stands out among North American Tadarida bats due to the possession of deep wrinkles on the upper part of their lip.

They also have a Z-shaped upper third molar, which they use for grinding insects.

These individuals have canines that are more prominent in males than in females. The wings are lengthy and narrow with pointed tips, which equips them for swift and straight flight patterns.

The color of their fur ranges from dark brown to grey. The Mexican free-tailed bat has large feet with distinctly long and white bristles.

Habitat

Mexican free-tailed bats prefer to roost in caves. They also live in buildings of any type as long as they are granted entry to openings and dark recesses in the ceilings or walls.

The bats can make roosting sites in any building irrespective of age, height, design, construction materials, human habitation, and compass orientation.

Caves need to have sufficient wall and ceiling spaces to fit millions of bats.

Before buildings were used as habitats, free-tailed bats in the southeastern part of the United States were probably roosted in the hollows of trees such as red mangrove, black mangrove, white mangrove, and cypress.

However, most of the bats in Florida seem to prefer buildings and other artificial structures over natural roosts. Caves in Florida tend to be inhabited mostly by the southeastern myotis.

These caves have pools of water on the floor, and the free-tailed bats do not require as much relative humidity as the southeastern myotis.

Diet

Mexican free-tailed bats are mostly insectivores. They make use of echolocation to hunt their prey. They feed on moths, beetles, dragonflies, flies, true bugs, wasps, and ants.

They usually capture flying prey in flight. Vast Mexican free-tailed bats fly several meters above Texas’s ground to feed on migrating insects.

These bats spend a good part of their active time searching for food while in the air. They preferably hunt at heights as high as 49 ft. Individuals can fly a distance of 50 kilometers per hour in one night to reach foraging areas.

The loose, wrinkled skin around their mouths is thought to boost their mouth’s expansion during flight to capture insects. The Mexican free-tailed bats require free water sources to keep up water balance.

On the other hand, these bats serve as food to large birds, such as the red-tailed hawk, American kestrels, great horned owls, barn owls, and Mississippi kites.

They also serve food to mammal predators such as Virginia opossums, striped skunks, and raccoons.

Habits

Mexican free-tailed bats are night feeders, and they commence feeding right after sunset. They travel as long as 50 km in a swift, direct flight pattern to feed.

Among the various species of bats, the Mexican free-tailed bats cruise at the highest altitudes. They fly at heights around 3300 meters above the ground.

These bats appear to be most active between June and September in the late morning and afternoon. Free-tailed bats are more attuned to and active in warm weather.

The method of measurement did not record wind speed and ground speed at the same time. It is presumed powerful local gusts could have impacted the observations, and the bat’s maximum airspeed remains unknown.

These bats are known for using echolocation when on the hunt; their calls are of a short but regular frequency. However, they alternate modulated frequency calls within 40-75kHz once something is detected.

Their frequency range of echolocation is usually between 49-70kHz, but it can drop to a range between 25-40kHz when something stumbles on their path during flight.  

Aaron Corcoran, a Wake Forest University, North Carolina biologist, reported online that he and his team had observed Mexican free-tailed bats producing ultrasonic vocalizations.

These vocalizations blocked the echolocation calls of a rival bat species on the hunt for moths. The ‘jamming’ call increased the chance of the rival bat missing its prey.

This leaves the prey for the Mexican free-tailed bat to feed on. Earlier researchers had observed about 15 variants of social calls produced by Mexican free-tailed bats.

They also disclosed that they could alternate their calls to avoid interfering with others within their call range.

Reproduction

The female bats assemble into maternity roosts during the mating season. The environment determines the size of these roosts, and caves usually have larger roosts.

Breeding can happen aggressively or passively. If aggressive, the male bat controls the female’s movements, keeping her at bay from the other bats in the roost.

The male also vocalizes during their mating. If passive, the male flies to a female in her roost and silently mounts her without resistance.

The Mexican free-tailed bats are promiscuous breeders, and males and females tend to copulate with several partners.

Female bats attain sexual maturity at nine months, while male bats attain sexual maturity in about two years.

The females enter here once a year, and their heat period usually lasts up to five weeks during spring.

Their gestation lasts for up to 12 weeks, and they give birth to only one offspring at a time. Their young are called pups, usually left in “creches” while the mother roosts elsewhere.

The females employ vocalizations and scents to identify their offspring. However, the pups try to snatch a suckle from any female bat that goes through the cluster.

The mother bathes the pup daily for about 4-7 weeks, and then they are weaned. By this time, the pup would have fully grown and become independent.

Conservation Status

Although some protection and efforts are now being made for the Mexican free-tailed bats due to habitat destruction, they are classified as “Least Concern.”