Sheath-Tailed Bats Sac-Winged Bats and Ghost Bats: Emballonuridae

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.