Ozark Big-eared Bat

Corynorhinus townsendii ingens

StatusEndangered
ListedNovember 30, 1979
FamilyVespertilionidae (Bats)
DescriptionLarge-eared, medium-sized, reddish bat.

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HabitatCaves in mature hardwood forests.
FoodInsects.
ReproductionOne or two young per season.
ThreatsHabitat disturbance
RangeArkansas, Missouri, Oklahoma

Description

The Ozark big-eared bat, Corynorhinus townsendii ingens, is a subspecies of Townsend"s big-eared bat. Adults weigh from 0.2-0.5 oz (5-13 g) and have prominent ears, 1 in (2.5 cm) long, connected across the forehead. The bat has mitten-shaped glands on the muzzle and elongated nostril openings.

Townsend"s big-eared bats resemble the eastern big-eared bat (Plecotus rafinesquii ), but can be distinguished by color. The brown-backed Townsend"s has tan underparts in contrast to the whitish underparts and gray back of the eastern big-eared bat. The Ozark big-eared bat can be distinguished from its near relative, the Rocky Mountain form (Plecotus townsendii pallescens ), by its reddish color and larger average size.

The species is also classified as Plecotus townsendii ingens.

Behavior

Townsend"s big-eared bat is fairly sedentary, migrating no more than 40 mi (64 km) between hibernation and maternity caves. It returns to the same roosts year after year, and caves are used year round. The bat usually hibernates near cave entrances just beyond the twilight zone, but during a heavy winter may move deeper inside the cave.

Bats hibernate singly and in clusters. Solitary bats hang upside down by one or both feet with wings wrapped around the body and interlocked. Wings of clustered bats are usually folded against the body, and the ears may be coiled tightly against extreme cold.

Ozark bats feed principally on moths and other insects. Some have been observed gleaning insects from leaves while perched, but most feed while in flight, locating insects through echolocation.

These bats follow a mating ritual that includes vocalization and head-nuzzling. Breeding begins in autumn and peaks in November. Young females mate in their first year. The male"s sperm is stored in the reproductive tracts of females until spring, when fertilization takes place. Gestation takes from 56 to 100 days.

Townsend"s bats are born hairless with their large ears draped down over unopened eyes for the first few days. Young bats are capable of flight at three weeks and are fully weaned at six weeks.

Habitat

Ozark big-eared bats inhabit caves typically located in limestone karst regions dominated by mature hardwood forests of hickory, beech, maple, and hemlock trees. Females bear and care for young in maternity caves. These caves are usually closer to food sources than the hibernation caves, which are better protected from the cold and wind.

Distribution

Non-endangered subspecies of Townsend"s big-eared bat, including P. t. townsendii, P. t. pallescens, and P. t. australis, are found throughout much of western North American from British Columbia south through California into Mexico, and east from the coast to a line extending from the Black Hills of South Dakota south through western Texas. A fourth subspecies, Virginia big-eared bat (P. t. virginianus ), is federally listed as Endangered.

Once fairly common, the Ozark big-eared bat is now limited to a few isolated populations in Arkansas, Missouri, and Oklahoma.

In 1986 a survey of 71 potentially habitable caves in Arkansas and Oklahoma located only four maternity caves that still harbored viable breeding colonies of the Ozark big-eared bat. These were Blue Heaven Cave in Marion County, Arkansas, and three unnamed caves in Adair County, Oklahoma. In addition, hibernation colonies were located in four caves in Marion and Washington counties, Arkansas, and Adair County, Oklahoma.

A census of the populations of the maternity caves was performed again in 1987, resulting in a minimum count of 450 Ozark big-eared bats, a slight increase over the previous year. In addition, biologists discovered a new maternity cave in Adair County that housed 260 bats, the largest known breeding colony. None of the known hibernation caves support more than 100 bats.

Seventeen caves in Adair, Cherokee, Delaware, and Sequoyah counties, Oklahoma, have been found to support a few solitary bats. Three caves in Marion and Washington counties, Arkansas, and four caves in Stone and Barry counties, Missouri, also sheltered isolated individuals. By 1992, the total population numbers were thought to be less than 1,000 individuals.

Threats

Not all factors limiting the Ozark big-eared bats are known. Although some predation occurs, loss of habitat does not seem to be a factor. A number of apparently suitable caves remain unoccupied. The most significant cause of this subspecies" overall decline is probably increased human intrusion into bat caves. Typically, bats only store enough calories to make it through the winter, and, when aroused from hibernation, they burn up these reserves. Disturbed bats often starve or are forced to leave hibernation prematurely in search of food. Bats also tend to abandon cave sites that are disturbed frequently.

Conservation and Recovery

Gates have been constructed at the entrances of some caves to keep out people and predators. The results have been mixed. Some gated caves seem to have restricted bats" access to the caves, and populations actually declined as a result. Gates have recently been redesigned to protect cave entrances without limiting bat egress. Cooperative agreements have been reached with owners of some caves to restrict human intrusion.

In 1988, lightweight radio transmitters were attached to female Ozark big-eared bats in Oklahoma to determine the feasibility of using telemetry in recovery efforts. While the bats appeared unencumbered, the short range of the radios used in the experiments limited the practicality of this effort to determine bats" reproductive activities.

In 1991, the U. S. Fish and Wildlife Service provided funds for bat cave protection at Devil"s Den State Park, a primary wintering home to the bats. The park"s popularity with visitors—a half-a-million a year—made cave protection difficult. Funds were used to install a customized alarm system to ward off intruders; though gating is the preferred habitat protection tool for such caves, the uneven, irregular shape of the landscape made such a barrier solution impractical at Devil"s Den.

Another major recovery effort in recent years was the transfer of a 255-acre (103.2-hectare) tract of Farmer"s Home Administration property containing caves and land important to the recovery of the Ozark big-eared bat to the Oklahoma Bat Caves National Wildlife Refuge. An agreement was negotiated with the Cherokee Nation to protect 120 acres (48.6 hectares) of tribal lands for the benefit of these endangered bats.

Contacts

U.S. Fish and Wildlife Service Regional Office, Division of Endangered Species P.O. Box 1306 Albuquerque, New Mexico 87103 http://southwest.fws.gov/

U.S. Fish and Wildlife Service Regional Office, Division of Endangered Species Federal Building Ft. Snelling Twin Cities, Minnesota 55111 http://midwest.fws.gov/

U.S. Fish and Wildlife Service Regional Office, Division of Endangered Species 1875 Century Blvd., Suite 200 Atlanta, Georgia 30345 http://southeast.fws.gov/

References

Harnish, H.E. 1992. "Protecting the Bats of Devil"s Den." BATS Magazine, 10(2): 13-18.

Harvey, M. J., et al. 1981. "Endangered Bats of Arkansas: Distribution, Status, Ecology, Management." Ecological Research Center, Memphis State University, Memphis.

Jacobs, J., and F. Bagley. 1984. "1983 Rangewide Survey of Ozark and Virginia Big-Eared Bat Maternity Colonies." U.S. Fish and Wildlife Service, Atlanta.

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U.S. Fish and Wildlife Service. 1984. "A Recovery Plan for the Ozark Big-Eared Bat and the Virginia Big-Eared Bat." U.S. Fish and Wildlife Service, Newton Corner, Massachusetts.