SAC-WINGED BATS, SHEATH-TAILED BATS, AND GHOST BAT FACTS
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 sacwinged 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.
Emballonurids live in the tropical and subtropical regions of the world, including Mexico, Argentina, Madagascar, and Southeast Asia.
WHERE DO GHOST BATS LIVE
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.
WHAT DO GHOST BATS EAT
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 sacwinged bat, and possibly other species, are monogamous (muhNAH-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.
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.