Bat, gray

Myotis grisescens

phylum: Chordata

class: Mammalia

order: Chiroptera

family: Vespertilionidae

status: Endangered, IUCN Endangered, ESA

range: Central and southeastern USA

Description and biology

Contrary to its name, the gray bat is reddish-brown in color. Its forearm measures 1.6 inches (4 centimeters) long, and it weighs 0.35 ounce (10 grams). The gray bat differs from other species of the Myotis genus (a group with similar characteristics) in that its wing membrane (a double membrane of skin) attaches to its ankle instead of the side of its foot. The gray bat feeds at night on insects, particularly mayflies and mosquitoes. It roosts in two different types of caves throughout the year.

Female gray bats begin hibernating immediately after mating in the fall; adult males and juveniles follow several weeks later. In late March, the females emerge from hibernation, while the rest emerge about a month later. Using sperm they have stored all winter, female gray bats fertilize their eggs after hibernation, giving birth to a single infant around late May.

Habitat and current distribution

In summer, while gray bats are raising their young, they roost in caves that have a temperature between 57 and 77°F (14 and 25°C). In winter, during hibernation, the bats roost in caves that have a temperature between 43 and 52°F (6 and 11°C). Gray bats are found in limestone caverns in Alabama, Arkansas, Georgia, Illinois, Indiana, Kansas, Kentucky, Mississippi, Missouri, North Carolina, Oklahoma, Tennessee, and Virginia. In 1980, scientists estimated the gray bat population to be less than 1,600,000.

History and conservation measures

Before the American Civil War (1861-65), millions of gray bats inhabited the southeastern United States. Beginning with the war, bat guano (feces) was used to produce saltpeter (potassium nitrate), a component of gunpowder. When humans entered roosting caves to collect the guano, the bats were disturbed from their normal routine. This was particularly harmful during hibernation. When aroused during this period, a gray bat is forced to use its stored fat and may starve to death before spring.

In modern times, spelunking (cave exploring), tourism, and flooding caused by the construction of dams have all led to the destruction of bat habitat. Between 1960 and 1980, the gray bat population decreased almost 80 percent. Water pollution and pesticides the bats ingested by eating contaminated insects also contributed to this decline.

Since the early 1980s, many bat caves have been protected from human disturbance, and the drop in the number of gray bats seems to have stopped. Without further conservation measures, however, the bats will not reach full recovery.