FREE-TAILED BATS AND MASTIFF BATS: Molossidae

PHYSICAL CHARACTERISTICS

Molossids (mol-LOSS-ids; members of the family Molossidae) range widely in size from small to moderately large bats. They have a forearm length of approximately 1.1 to 3.4 inches (2.7 to 8.5 centimeters), and weigh from 0.2 to 3.8 ounces (5 to 167 grams). Free-tailed bats are named for their thick tail that extends far beyond the tail membrane (thin layer of skin). The mastiff bats are named after their facial resemblance to the mastiff dog.

Some species of molossids have a distinctive wrinkled upper lip, while others have a smooth upper lip. Muzzles of all these bats are generally short and wide and often have wide, fleshy lips that may have folds or creases. Many have a distinctive pad over their noses. The upper surface of this pad often has small horn-like projections. Ears of free-tailed bats are relatively short and thick, often joined across the forehead and point directly forward. The eyes of these bats are relatively small, while the lips are large. All species have long and narrow wings that are thick and, along with the tail, are covered in a leathery membrane. Molossids also have short, strong legs and broad feet. On the outer toes of each foot are curved bristles that the bat uses for grooming its fur.

Molossids generally have short, velvety fur. One group of bats in this family is called the hairless bats because their hair is so short that the animal appears to be naked. Some species have a crest of hairs on the top of the head that stands upright. Fur color may be gray, tan, black, or brown. Many species have two color phases, or types, a reddish one and brownish or blackish color phase.

GEOGRAPHIC RANGE

Molossids are found throughout the world's warmer areas. They are primarily found in South America and Africa, as well as from southern Europe and southern Asia through Malaysia, and east to the Fiji Islands. They are also found in the central and southern part of the United States, south through the West Indies, Mexico, and Central America to the southern half of South America. Except for one other family of bats, the Vespertilionidae, molossids are found in the widest geographic area.

HABITAT

With molossids spread out all over the world, they are found living in a wide range of habitats. They are commonly found in both natural and urban areas. These bats are most plentiful in arid (extremely dry) and semi-arid conditions. They prefer to live in temperatures that are at least 110°F (43°C). These bats roost (rest or settle) in sites such as caves, tunnels, buildings, hollow trees, foliage, decayed logs, and holes in the ground. They also shelter under bark, rocks, and iron rooftops.

DIET

Molissids eat a variety of insects, such as moths and ones with hard shells, such as beetles and stinkbugs.

BEHAVIOR AND REPRODUCTION

Molossids are generally strong flyers that can fly quickly for long periods of time. Like all bats, these bats are nocturnal, meaning they are active at night. These bats fly all night, whereas other bats typically fly a short time during the night. They can fly six or seven hours without stopping.

Molossids catch their prey using echolocation (eck-oh-loh-KAY-shun), a technique where the bat detects objects by receiving the reflection of sounds it produces. They fly with their mouths open and send out echolocation calls. They forage, search for food, in groups and head towards large swarms of insects. They also look for food around streetlights, which attract insects, such as moths. They generally catch their prey while they are flying.

Because they live in warm areas, molossids do not need to hibernate (become inactive in the cooler months to conserve energy). Some of these bats travel to even warmer areas in the winter.

Molossids have a range of roosting habits, from solitary to social, living in large colonies (groups) of millions of individuals. Between those two extremes, sizes of colonies range from hundreds to thousands of individuals. Most of these bats do form colonies in the size of a few tens to several hundred individuals. Molossids generally return to their roosting sites every year. Their colonies generally give off a strong, musky odor.

THAT'S A LOT OF GUANO

A colony with thousands or millions of bats will produce a lot of guano, and people have been putting these droppings to use for a long time. Before people began to sell guano as fertilizer, the Confederate Army was using guano during the Civil War (1861–1865), as a source of gunpowder. It is thought that this guano was collected from the Brazilian free-tailed bat. In the late 1800s came the discovery of the millions of bats in Carlsbad Caverns, New Mexico, and their associated guano, which was valuable. In the early 1900s mining operations started in the caves, using mining cars to transport guano to the cave entrance. Most of the guano was shipped to southern California to help the developing citrus industry. In about twenty years of operation, over 100,000 tons of guano was taken from Carlsbad Cavern. Six companies attempted to make a profit in this venture, but all failed due largely to high transportation costs. Bat droppings in Carlsbad Caverns over the past 17,000 years have formed guano deposits covering several thousand square feet to a depth of almost 50 feet (15 meters)!

Little is known about the mating habits of most molossids. Most species are considered polygynous (puh-LIJ-uh-nus), meaning the male mates with more than one female during the mating season. Females of most species appear to produce one offspring per year. Two young are born on rare occasions, and the black mastiff bat in Trinidad possibly has two litters per year. During pregnancy, females generally form maternity colonies that are separate from the males. In these colonies, females relocate and nurse their young independently.

MOLOSSIDS AND PEOPLE

Like many insect-eating bats, molossids eat many insects that humans consider to be pests. The one hundred million Mexican free-tailed bats that live in Texas in the summer eat an estimated 1,000 tons (907 metric tons) of insects each night, many of which destroy crops. In California and other areas, farmers build bats houses to attract these bats so they will eat the pests. People also collect the bat droppings (guano; GWAH-no) of molossid bats that live in large colonies, using the guano as a fertilizer as it is rich in nitrogen. Some species of these bats have also been associated with spreading disease, such as rabies. Rabies is a viral infection that attacks the nervous system and can be deadly.

People have caused the decrease in population of molossids by destroying and disturbing their natural habitat. These bats have also been harmed through eating insects that have come into contact with pesticides, chemicals designed to control pests.

CONSERVATION STATUS

The survival of many of these species is under threat. The IUCN lists Gallagher's free-tailed bat, Niangara free-tailed bat, and Wroughton free-tailed bat, as Critically Endangered, meaning they face an extremely high risk of extinction in the wild. The Incan little mastiff bat is listed as Endangered, meaning it faces a very high risk of extinction in the wild. Fifteen other species are listed as Vulnerable, meaning they face a high risk of extinction in the wild.

Naked bat (Cheiromeles torquatus)

NAKED BAT (Cheiromeles torquatus): SPECIES ACCOUNTS

Physical characteristics: Naked bats are the largest molossids, with a head and body length ranging from 4.5 to 5.8 inches (11.5 to 14.5 centimeters). They weigh from 3.2 to 5.7 ounces (96 to 170 grams). Also called naked bulldog bats, these bats are almost completely hairless. They have scattered short hairs and bits of longer hair around a scent gland on their neck. This haired gland produces a strong, foul odor.

These bats have loose, dark gray, brown, or black skin. A naked bat has bristles on its toes, which it uses for cleaning and grooming. Another distinguishing characteristic of the bat is the pocket of skin along its sides. These flaps of skin form a wing pouch that the bat folds its wings into when it rests. Ears are separate and their lips are smooth. Big toes have a flat nail instead of the typical claw.

Geographic range: Naked bats are found in Southeast Asia, including Malaysia, Borneo, Java, Sumatra, the Philippines, and surrounding islands.

Habitat: These bats live in tropical forests and several live on islands. They roost in caves, rock crevices, tree hollows, and holes in the ground.

Diet: Naked bats feed on insects, primarily termites and winged ants.

Behavior and reproduction: Naked bats are strong, fast fliers. They fly high above the forest canopy (the tops of trees) or above clearings to forage, or search, for food. When they fold their wings into their pouch, these bats can move about relatively easily on all four limbs.

This species of bat roosts in large colonies. Nearly a thousand individuals were observed in a hollow tree, and a colony of about 20,000 was observed in a cave in Borneo.

There are usually two offspring. The young are most likely left in the roost when the parents leave to forage for food in the evening.

Naked bats and people: In certain areas, most of the forest habitat of the naked bat has been destroyed by development, logging, and cultivation. People have hunted these bats for food and killed them because they mistakenly believed these bats were harming their crops.

Conservation status: The IUCN Red List categorizes these bats as Near Threatened, not currently threatened, but could become so. In specific areas, this species has significantly declined, and is protected by law. ∎

BRAZILIAN FREE-TAILED BAT (Tadarida brasiliensis): SPECIES ACCOUNTS

Physical characteristics: Also called the Mexican free-tailed bat, Brazilian free-tailed bats are small to medium in size, with a total head and body length of approximately 3.8 inches (9.5 centimeters).

Geographic range: Brazilian free-tailed bats are found in the southern half of the United States, as well as Mexico, Central America, South America to southern Chile and Argentina, and much of the Lesser and Greater Antilles.

Habitat: Brazilian free-tailed bats are primarily found in arid and semi-arid habitats. They are also found in urban areas, moist forests, and grassland areas. These bats roost in caves, mine tunnels, tree hollows, and under bridges. They also are frequently found in and around buildings.

Diet: These bats feed on a range of insects, including moths, beetles, weevils, mosquitoes, flying ants, and leafhoppers.

Behavior and reproduction: Brazilian free-tailed bats are best known for their immense roosting colonies. While roosts of several dozen have been found, these bats also roost in colonies that reach the millions. A colony that lives in Bracken Cave, Texas, makes up the largest colony of mammals in the world, with an estimated twenty million individuals in this summertime maternity colony. They fly high above the ground when foraging for prey, except when sweeping over a body of water to drink.

Mating among these bats is considered promiscuous (prah-MISS-kyoo-us), meaning males and females mate with more than one other bat. Females bear a single offspring once a year in May to July. In maternity roosts where millions of bats are packed tightly together, mothers are able to identify and nurse their own young.

Brazilian free-tailed bats and people: Many of the insects these bats eat are considered pests by humans. These bats are also known carriers of rabies.

Conservation status: Many of the large colonies have declined dra-matically in numbers. The IUCN lists Brazilian free-tailed bats as Near Threatened. ∎

FOR MORE INFORMATION

Books:

Fenton, M. Brock. Bats. New York: Checkmark Press, 2001.

Fenton, M. Brock. The Bat: Wings in the Night Sky. Buffalo, NY: Firefly Books, 1998.

Nowak, Ronald M. "Free-tailed Bats and Mastiff Bats." Walker's Mammals of the World 5.1 Online. Baltimore: Johns Hopkins University Press, 1997. http://www.press.jhu.edu/books/walkers_mammals_of_the_world/chiroptera/chiroptera.molossidae.html (accessed on July 5, 2004).

Raabe, Emily. Free-Tailed Bats. New York: Powerkids Press, 2003.

Richardson, Phil. Bats. London: Whittet Books, 1985.

Ruff, Sue, and Don E. Wilson. Bats. New York: Benchmark Books, 2001.

Schober, Wilfried, and Eckard Grimmberger. The Bats of Europe and North America. Neptune City, NJ: T.F.H. Publications, Inc., 1997.

Periodicals:

Bowers, Barbara. "Going to Bat for the Bats." Audubon (December 2003): 86

Finnegan, Lora J. "Bats about Bats." Sunset (July 1993): 38

Kerner, Sarah. "In the Bat Cave: These Guys Got an Up-close Look at One of the World's Most Misunderstood Creatures. Lesson Learned: Bats get a Bad Rap!" Boys' Life (June 2003): 18

McCracken, Gary F., and John K. Westbrook. "Bat Patrol: Scientists Discover That High-flying Mammals are Bad News for Bugs." National Geographic (April 2002): 114

Vine, Katy. "Pow (Going Batty)!" Texas Monthly (January 2004)

"Wings in the Dark." Weekly Reader (October 31, 2003): 4

Web sites:

"Natural Resources: The Bat Colony." Carlsbad Caverns National Park: National Park Service. http://www.nps.gov/cave/bats.htm (accessed on July 5, 2004).

"Discover the Secret World of Bats." Bat Conservational International, Inc. http://www.batcon.org (accessed on July 5, 2004).

Kee, Lim Gaik. "Bats are Pollinators not Pests." Nature Watch. http://habitatnews.nus.edu.sg/pub/naturewatch/text/a062b.htm (accessed on July 5, 2004).

"Malaysian Bat Conservation." EarthWatch Institute. http://www.earthwatch.org/expeditions/kingston/meetthescientists.html (accessed on July 5, 2004).

"Naked Bat (Cheiromeles torquatus)." The Forest Department: Sarawak, Malaysia. http://www.forestry.sarawak.gov.my/forweb/wildlife/mgmt/tpa/nbat.htm (accessed on July 5, 2004).

Myers, P. "Family Molossidae (Free-tailed Bats)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Molossidae.html (accessed on July 5, 2004).