Mexican free-tailed bat, Tadarida brasiliensis
The Mexican free-tailed bat (Tadarida brasiliensis), is a native bat to the Americas. It has a range that stretches from Oregon, Nevada, Utah, Nebraska, and other states in the north to southern areas in most of Southern America and Mexico. This bat’s South American range is not understood and it lives in four of the seven faunal regions of South America. Its habitats include places like the pacific coast Peru, Chile, the eastern slopes of the Andes, and the eastern Brazilian highlands and coast. It can also be found in 11 of the Lesser Antilles and all of the Greater Antilles. Even with this wide range, the Mexican free-tailed bat cannot be found in much of the Amazon rainforest.
Mexican free-tailed bats are of medium size, with an average body length of 3.5 inches, with the tail comprising nearly half of the total length. They can weigh an average of .43 ounces. The fur on this bat can vary from greys to browns. It has a distinctly short nose and the lips are wrinkled. The eyes of the Mexican free-tailed bat are set widely apart, allowing the bet to spot prey better when using echolocation. The free-tailed bat gets its name from its tail that extends far past the uropatagium, the membrane that extends past the thighs and often includes the tail.
Preferring habitats in caves, Mexican free-tailed bats will live in huge colonies, and as a result have few colonies. They will also roost in abandoned buildings. These bats will live practically anywhere that is suitable, requiring openings and dark hollows to roost under. Factors like age, building material, past human occupation architecture and compass orientation do not affect the bat’s ability to roost in manmade structures. A colony of bats in Houston, Texas (numbering 250,00), roosts under Waugh Street Bridge over Buffalo Bayou, attracting many on lookers. If bats are roosting in a cave, they require large amounts of space to accommodate their populations reaching far into the millions.
In the southeastern United States, the natural habitats of the free-tailed bats probably included hollow trees like cypress, both black and white mangrove, and red mangrove. In Florida, free-tailed bats do not prefer to occupy caves, as they do not require the humidity found in them like southern myotis bats. The largest colony of bats found in one cave resides north of San Antonio, Texas, in Bracken Cave, numbering almost twenty million bats.
The Mexican free-tailed bat migrates to many places, depending on its location Bats located in southeastern California and Nevada, western Arizona, and south western Utah migrate to Baja and southern California as one unit. Bats found in southeastern Utah, eastern Arizona, southwestern Colorado, and western New Mexico choose to migrate to the western side of the Sierra Madre Oriental and into Jalisco. They will also migrate to Sinaloa and Sonora. A few bats that spend the summer in eastern New Mexico and Texas, Kansas, and Oklahoma will move south, towards southern Texas and even into Mexico. One colony who migrates north during the summer to Austin, Texas from Mexico roosts under the Congress Avenue Bridge, a mere ten blocks from the State Capital. These bats attract approximately 100,000 tourists each year, who come to the bridge to observe them. Every night they will eat ten thousand to thirty thousand pounds of food. Bats located in eastern Texas, ranging eastward from there, do not migrate but they will often switch caves. One regional population that can be found from Oregon to California will spend the entire year in their habitat.
These bats will begin their nightly hunts for food at around sunset, and will feed throughout the night, and they can fly as far as thirty-one miles from their home. Flying at heights of up to 10,825 feet, these bats have the highest recorded flight altitude. A group of bats found in a Colorado mine is active during the early morning, and even during the afternoon in the months of June to September. These bats are more likely to be active when there is warm weather. Free-tailed bats will use echolocation to fly and to look for food. During travel, they will send out brief calls, but when food or an object has been detected, they will switch to adjusted calls ranging between 75 to 40 kHz. An average frequency range for the Mexican free-tailed bat is between 49 to 70 kHz, but they can reach lower frequencies between 25 to 40 kHz. Mainly insectivores, Mexican free-tailed bats will eat moths, beetles, flies, true bugs, dragonflies, ants and wasps. Most bat prey are flying insects, as bats will fly when catching food rather than landing.
There are many predators of the Mexican free-tailed bat including barn owls, great horned owls, American kestrels, Red-tailed hawk, Mississippi kites, Virginia opossums, raccoons, and striped skunks. Eastern coral snakes and eastern coachwhips may also prey on free-tailed bats. In the United States, free-tailed bats have a low amount of rabies, although they do contain certain pesticides. One common killer of young free-tailed bats is a certain type of beetle. Due to evidence found in the bones, the oldest known bat lived to be eight years old.
The Mexican free-tailed bat has a specific routine for mating. Females will roost in colonies together found in cave, but they can also be found under manmade structures including buildings and bridges. Males will mark territory and call out to females in order to attract possible mates. After both males and females reach each other by calling out they will remove themselves from the group to begin mating. There are two types of mating styles for these bats. During aggressive mating, the male will separate the female from the group and restrict her movements, emitting distinct calls in the process. The passive form of mating entails remaining in a group or cluster, and the male will slowly climb onto a female. He will not make any noise while mating passively.
Female free-tailed bats can mate only once a year, during a period lasting about five weeks. They are able to have one baby per year, and will leave the baby in a large group of other young called a creche. Pups produce an odor that allows the mother to identify it, and they will also emit calls to find each other. Even with this bond, pups will try to get food from any mother bat, by latching onto her as she is flying. At four to seven weeks young bats are weaned, and are able to fend for themselves.
The Mexican free-tailed bat is listed in the IUCN Red List as of least concern, yet it is considered to be a species of special concern. Its roosting habits make it easy for human interactions to harm the bat populations. Habitat destruction is one cause for their declining populations. These populations are usually local, and measures have been taken to help save these bats. In a cave called Cueva de la Boca near Monterrey, Mexico, many endangered species including Mexican free-tailed bats are being protected by the Mexican environmental conservation (NGO), Pronatura Noreste. They purchased the property after 95 percent of the bats original population of twenty million bats was destroyed. Vandalism, uncontrolled tourism, and pollution were all to blame for the loss of these bats. They purchased the property in 2006, and have been able to preserve the remaining bat population, as well as other important species.
The Mexican free-tailed bat is the state bat for both Texas and Oklahoma. It is known as the most widely-distributed mammal in North America, and is Texas’ official flying mammal. The Bacardi rum brand uses the bat as its icon.
Image Caption: Mexican free-tailed bat, Tadarida brasiliensis. Credit NPS/Wikipedia