SAC-WINGED BATS, SHEATH-TAILED BATS, AND GHOST BATS: Emballonuridae

PHYSICAL CHARACTERISTICS

Emballonurids (bats in the family Emballonuridae) are small to medium in size. Their head and body length is about 1.4 to 6.3 inches (36 to 160 millimeters). They can weigh from 0.1 to 3.5 ounces (3 to 100 grams), about the weight of a first-class letter. These bats have thirty to thirty-four teeth.

For the most part, emballonurids are brown or gray in color, but this family also includes the whitish ghost bats in the genus Diclidurus, and bats with a pair of white stripes down their back in the genus Saccopteryx. Emballonurids have a smooth face and lips with relatively large eyes. Their ears are usually round and cup-shaped, often joined by a band of skin across the forehead. The ears have a tragus (TRAY-gus), a flap that projects from the inner ear. Researchers theorize the tragus plays some role in echolocation (eck-oh-loh-KAY-shun), the process of sending out high-pitched sounds and identifying objects by interpreting the sound when it bounces back.

Some emballonurids are also known as sheath-tailed bats because of their tail. They have a short tail that juts out from the membrane (double layer of thin skin) between their legs, and when their legs are stretched out their tail appears to be sheathed in the membrane. Another name for some emballonurids is sac-winged bats, referring to the glandular sacs in their wing membranes. Glandular sacs produce and release substances for use in the body. In this case they contain a liquid with a strong odor. In the sac-winged bats these sacs are more pronounced in males. The position and size of these sacs differs depending upon the species.

GEOGRAPHIC RANGE

Emballonurids live in the tropical and subtropical regions of the world, including Mexico, Argentina, Madagascar, and Southeast Asia.

HABITAT

Emballonuridae bats generally live in humid rainforests. These bats tend to roost, rest or settle, in areas that are relatively light compared to what other bat families prefer. Their roosts include the entry areas to caves and other structures, the outside of buildings, hollow trees, and leaves.

DIET

Emballonurids eat primarily insects, although they have been seen eating fruit. They generally eat insects while flying, yet some species are known to look for their food along the ground. These bats start foraging, searching for food, relatively early in the day compared to other bats. Some of these bats such as the ghost bats, capture their meals while flying high in the open air. Other bats, such as the proboscis bat, hunt insects above or close to water surfaces.

BEHAVIOR AND REPRODUCTION

By pulling their hind legs together or apart during flight, the emballonurids can shorten or lengthen their membrane. This gives these bats tremendous control as they steer, maneuver, and turn in flight. Like all bats, they are nocturnal, resting during the day and becoming active at night. During bad weather, some species forage in the afternoon.

Some emballonurids roost in large groups, others gather in smaller groups of about ten to forty, and a few are loners. Colonies of African sheath-tailed bats include up to 50,000 bats, each of which returns to a precise place in a roosting cave along the Kenyan coast. Daytime roosts for the sac-winged bat can reach up to sixty individuals. Proboscis bat females roost apart from the males when the young are born. Different shelters are used by adult male and female gray sac-winged bats during the summer; most of the other forms seem to remain together throughout the year.

Some emballonurids, such as the greater sac-winged bat, live in year-round stable harems (HARE-um; group of females associated with one male), with one to eight females in an area that is patrolled by a male. Male sac-winged bats in the genus Saccopteryx defend their harems with energetic flight maneuvers. Researchers have found that harem males father an average of 30 percent of the offspring within their harem. The majority of offspring is fathered by other harem males or by males from outside the colony.

Some of these bats perform elaborate mating rituals. The social calls they emit are audible to humans. For species in which the males have sacs in the front wing membrane containing a liquid with a strong scent, the males fan the odor towards the females while hovering around them. Each afternoon, male Saccopteryx bats store a cocktail of perfume in their wing sacs that consists of urine, saliva and other bodily secretions.

There is a variety of different mating customs among the different species of emballonurids. Most of these bats are polygamous (puh-LIH-guh-mus), meaning that males mate with more than one female during the mating season. Yet the chestnut sac-winged bat, and possibly other species, are monogamous (muh-NAH-guh-mus), meaning a male and female mate and pair only with each other.

Emballonurids generally give birth to a single offspring each year. An exception is the small proboscis bat that reproduces twice a year. Most emballonurid females give birth to their offspring at the beginning of the rainy season.

EMBALLONURIDS AND PEOPLE

Because emballonurids prefer roosting in open areas, these bats are among the more common bats for people to spot. They can be seen in trees, on buildings, and at the edges of caves. The social calls they emit are also within human hearing range. Some emballonurids are declining due to human destruction of their natural habitat.

THE FIRST FOSSILS

Emballonurids were first recorded in Europe thirty-eight to fifty-four million years ago.

CONSERVATION STATUS

There are several emballonurid species that are endangered or threatened with becoming endangered. The IUCN lists two species as Critically Endangered, facing an extremely high risk of extinction in the wild; two species as Endangered, facing a very high risk of extinction in the wild; and ten species as Vulnerable, facing a high risk of extinction in the wild.

GREATER SAC-WINGED BAT (Saccopteryx bilineata): SPECIES ACCOUNTS

Physical characteristics: Greater sac-winged bats are relatively small, with a body length of 1.8 to 2.2 inches (47 to 56 millimeters). These bats are also called greater white-lined bats, referring to the two white lines that run down their bodies. Their fur is typically dark brown, while the underside is typically gray. These bats have dark wings, long noses, and the females are slightly larger than the males.

Geographic range: Greater sac-winged bats live in Central and South America; from south Mexico to southeast Brazil.

Habitat: Greater sac-winged bats live in lowland evergreen or semi-deciduous forests. They roost in relatively open areas, such as hollow trees and occasionally in buildings.

Diet: Greater sac-winged bats feed on insects.

Behavior and reproduction: Greater sac-winged bats are among the most common bats seen in the rainforest because they often roost on the outer parts of large trees. They use echolocation to locate their prey and then catch the insects while flying. Echolocation is a process by which the bats emit a variety of sounds and use the echoes from the sounds to identify objects around them. These bats are unusual in that males sing songs to females during the day in their colonies. These bats have been found roosting in relatively large colonies of sixty individuals. Within those colonies there can be smaller groupings of one to nine females. As seasons change, colonies move between different areas to forage for food.

Females give birth to a single offspring each year, typically at the beginning of the rainy season in July or August. It is thought these bats are polygamous, meaning that they have more than one mate during the mating season.

Greater sac-winged bats and people: There is no known significant relationship between greater sac-winged bats and people.

Conservation status: Greater sac-winged bats are not listed as threatened. ∎

GREATER DOG-FACED BAT (Peropteryx kappleri): SPECIES ACCOUNTS

Physical characteristics: Greater dog-faced bats are also referred to as greater dog-like bats. These bats are relatively small, with a head and body length of 2.5 to 2.9 inches (63 to 75 millimeters). Their fur is typically dark or reddish brown and their underside is paler in color. Tufts of hair cover the head. The ears are separated at the base and are usually, along with the wings, black in coloration. Males are generally slightly larger than females.

Geographic range: Greater dog-faced bats live in southern Mexico to Peru and southern Brazil.

Habitat: Greater dog-faced bats have been found in forests, swamps, and savanna (grassland). They roost in small, shallow caves, holes in trees, and under fallen logs where light can enter. A study in Costa Rica found these bats roost about 39 inches (1 meter) from the ground.

Diet: Greater dog-faced bats eat insects.

Behavior and reproduction: Greater dog-faced bats have been found in Costa Rica to roost in colonies of one to six individuals. Usually there were several adults of each sex in the group. One unique behavior is that males sit on top of females. This implies that the male bat is protecting or guarding the female and that the females and males could be monogamous. At the beginning of the rainy season females give birth to a single offspring.

Greater dog-faced bats and people: There is no known significant relationship between greater dog-faced bats and people.

Conservation status: Greater dog-winged bats are not listed as threatened. ∎

FOR MORE INFORMATION

Books:

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

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

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:

Milius, S. "Male Bats Primp Daily for Odor Display." Science News (January 1, 2000): 557–557.

Nowak, Ronald M. "Ghost Bats or White Bats." Walker's Mammals of the World 5.1 Online.http://www.press.jhu.edu/books/walkers_mammals_of_the_world/chiroptera/chiroptera.emballonuridae.diclidurus.html (accessed on July 2, 2004).

Schnitzer, Hans-Ulrich, and Elisabeth K. V. Kalko. "Echolocation by Insect-Eating Bats." Bioscience (July 2001): 557–557.

Web sites:

"Bats in Australia." Australian Museum Online. http://www.austmus.gov.au/bats/records/bat24.htm (accessed on July 2, 2004).

"Ghost Bat—Macroderma gigas." UNEP World Conservation Monitoring Centre. http://www.unep-wcmc.org/index.html?http://www.unep-wcmc.org/species/data/species_sheets/ghostbat.htm~main (accessed on July 2, 2004).

"Monkeying Around! The Mammals of Southeast Asia." Focus on Wildlife. http://www.ecologyasia.com/FOW_Pages/mammals.htm (accessed on July 2, 2004).

Simmons, Nancy. "Saccopteryx bilineata, Greater Sac-winged Bat." American Museum of Natural History. http://www.digimorph.org/specimens/Saccopteryx_bilineata/whole/ (accessed on July 2, 2004).

Voigt, Christian C. "The Sac-Winged Bat Project." Institute for Zoo and Wildlife Research. http://www.izw-berlin.de/en/research/fg1/index.html?themen/themen.html~rechts (accessed on July 2, 2004).