Gray Sac-Winged Bat, Balantiopteryx plicata

The gray sac-winged bat (Balantiopteryx plicata), sometimes known as Peter’s sac winged bat, can be found in Mexico. Its range extends from Sonora and Baja California Sur to Nicaragua, Costa Rica, El Salvador, Honduras, Guatemala, and northern areas of Colombia. It prefers a habitat in open areas, like evergreen forests and can be found at elevations of up to 4,912 feet.

The gray sac-winged bat was first described in 1867 by Wilhelm Peters. It received its scientific name plicata from the Latin term that means folded. Its genus name, Balantiopteryx, is derived from the Greek term meaning pouch wing. This species hold two recognized species known as Balantiopteryx plicata pallida and Balantiopteryx plicata plicata.

The gray sac-winged bat can reach an average body length of 2.6 inches, with males weighing an average of .2 ounces and females weighing slightly more. This species is classified in the Emballonuridae family, also known as sheath tail bats, and displays the trait common to all members of that family. Its tail is almost completely covered by a membrane that extends from one ankle to the other. This species received its common name from the sacs located on its wings.

These grow larger in males than in females and are found between the neck and wrist on each wing. The sac has an opening located near its base, and there have reports that the inside of the sac is white in color, although other reports say that the coloring depends on seasonal factors and the age of the bat.  The main coloring of this bat can vary between gray and dark brown, but each bat has white tipped fur and a lighter underbelly.

As is typical to bat species, the gray sac-winged bat is social and will gather colonies of fifty or more individuals. It has been reported that colonies can reach up to ten thousand bats. Studies have shown that females comprise seventy-five percent of the colonies, while males comprise only twenty-five percent. However, the contents of a colony depend on the season and other variables. Males were found to join a colony in higher numbers during the breeding season or the dry season. Once the males left the roost to other areas, females were found to remain. Colonies often hold other species of bats, and individuals are not known to be territorial.

The roosts of the gray sac-winged bat typically occur in arid areas, like barns or caves. Each roost must have a humidity level of at least twenty-five percent, and it is preferred that the roost have many exits. The bats will roost about 7.8 inches apart, with the exception of mothers and their young, and will typically face the same direction.

The breeding season for the gray sac-winged bat occurs at different times depending upon the area of its range. Individuals located in Central America typically mate between the months of January and February, while bats located in El Salvador were found to be pregnant  in May. Birthing also depends on the location of each colony, with bats in Mexico giving birth between the months of June to July. In order to find a mate, males will display courtship behaviors, which consist of flying around objects in large numbers. It is thought that the males release a scent from their wing sacs while courting females.

Female gray sac-winged bats can breed once a year and after a pregnancy period of about four to five months, each female will give birth to one pup. The pup is carried by its mother for the first week of its life, but can fly at two weeks of age and is weaned at about nine weeks of age. Unlike other species of bat, females of this species will not abort their young if food is not abundant, but will choose to give birth when conditions are optimal. When mothers leave to forage, pups will stay behind, latched onto the wall of their roost.

The diet of the gray sac-winged bat consists of many types of insects that are available seasonally. This species is known as an opportunistic forager, because it does not have any preference towards types of insects. Because of this, colony numbers do not depend on the availability of food and remain relatively consistent throughout the year. These bats will not forage in the same area for long periods, instead moving from area to area as needed. They can be foraging in groups or alone, at least one mile away from the roost. However, larger groups will travel across larger areas in order to consume enough food.

The flight pattern of the gray-sac-winged bat is typically slow and heavy. Studies conducted regarding the eyesight of this species have shown that when it is capable of sight, it will typically use the sense more than its echolocation. This was proven when experts placed a small number of bats in a greenhouse constructed from mesh and observed them for twenty-four hours. During the dawn, day, and dusk hours, when the bats were able to see, they repeatedly flew into the mesh. However, during the nighttime hours, when the bats were not able to see and had to use echolocation, they avoided the mesh of the greenhouse. This study showed that, although the bats preferred to use eyesight, their echolocation sense was more efficient.

The gray sac-winged bat is hunted by barn owls and spotted skunks, but it may also become prey to hawks, coatis, and domesticated cats. Like many species of bat, this species can get a number of external parasites including bat flies, fleas, red mites, lice, and ticks. Internal parasites include nematodes, cestodes, and Trematodes. Although many bats can contract rabies, this species is not thought to be highly susceptible to it. The main threat to this species is habitat loss caused by man made fires and human caused roost disturbances. Because the gray sac-winged bat occurs in such a large range and is not highly threatened by its threats, it appears on the IUCN Red List with a conservation status of “Least Concern.”

Image Caption: Gray Sac-winged Bat. Credit: Ruestz/Wikipedia (CC BY-SA 2.5)