Townsend’s Big-eared Bat


The Townsend’s big-eared bat is named for its large ears, which are from 1 to 1.6 inches (2.5 to 4 centimeters) long. In contrast, the bat’s body length is 1.8 to 2.7 inches (4.5 to 7 centimeters), its tail length is 1.4 to 2.1 inches (3.5 to 5.3 centimeters), and its forearm length is 1.4 to 2 inches (3.5 to 5 centimeters). The average Townsend’s big-eared bat weighs between 0.18 and 0.46 ounce (5 and 13 grams).

Townsend’s big-eared bats feed primarily on moths, which they locate through echolocation (sonar). In this process, a bat emits high-pitched sounds that echo or bounce off its prey. The bat’s sensitive hearing picks up the echo. From that sound, the bat can determine the size, shape, and location of its prey.

Male and female Townsend’s big-eared bats come together in late fall or early winter to mate and hibernate. The females store the sperm until early spring, when they fertilize their eggs. After a gestation (pregnancy) period of 56 to 100 days, they give birth to a single infant, which they nurse until fall.

There are five subspecies of Townsend’s big-eared bat, two of which are considered endangered under the Endangered Species Act: the Ozark big-eared bat (Plecotus townsendii ingens) and the Virginia big-eared bat (Plecotus townsendii virginianus).

Habitat and current distribution

Townsend’s big-eared bats are found in forest and desert areas in southwestern Canada, western United States, and Mexico. The bats inhabit caves, abandoned mines, and, sometimes, buildings. They prefer limestone caves, however.

Like many other species of bats, Townsend’s big-eared bats hibernate in one type of cave while raising their young in another. They will often use these same sites year after year.

The gray and white Ozark big-eared bats are found only in a few caves in Arkansas, Missouri, and Oklahoma. Biologists (people who study living organisms) estimate their population to be under 700. The predominantly gray Virginia big-eared bats are found in eastern Kentucky, southwestern Virginia, and eastern West Virginia. They number approximately 11,000.


History and conservation measures

Human disturbance is the primary reason for the decline in the number of Townsend’s big-eared bats. If disturbed while hibernating, the bats will often leave their roosts. Forced to rely on their stored fat for food, the bats often starve to death before winter is over.

The U.S. government has designated as critical habitats those caves known to be occupied by Townsend’s big-eared bats. This act prevents federal agencies from carrying out programs that would lead to the disturbance or destruction of these caves. However, this act has not deterred vandals and curious tourists from continuing to enter protected caves.

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