Virginia Big-eared Bat

Corynorhinus townsendii virginianus

Description

The Virginia big-eared bat, Corynorhinus (=Plecotus) townsendii virginianus, a subspecies of Townsend's big-eared bat, weighs from 0.17-0.45 oz (5-13 g) and has prominent ears, up to 1 in (2.5 cm) long and connected across the forehead. This sub-species has mitten-shaped glands on the muzzle and elongated nostril openings. It closely resembles the Endangered Ozark big-eared bat (Corynorhinus (=Plecotus) townsendii ingens ) but is sooty gray in color and slightly smaller.

Behavior

The Virginia big-eared bat is fairly sedentary, migrating no more than about 40 mi (64 km) between hibernation and maternity caves. It returns to the same roosts year after year and prefers cool, well-ventilated caves for hibernation. Bats hibernate singly and in clusters, hanging upside-down with wings wrapped around the body and interlocked. This bat feeds principally on moths and other insects, which it locates while in flight, using echolocation. The efficiency of its "radar" is enhanced by the large ears, which concentrate sounds.

Breeding begins in autumn and peaks in November. Copulation is preceded by a ritualized precopulatory behavior characterized by the production of audible vocalizations, followed by head nuzzling which may be directed at either torpid or active individuals. Young males fail to reach sexual maturity in their first autumn. Females mate in their first year and store the male's sperm until spring, when fertilization takes place. Gestation takes from 56 to 100 days. Typically, each female bears one or two young. Young are born hairless, with their large ears draped over unopened eyes for the first few days. They are capable of flight at three weeks and are fully weaned at six weeks.

Research has found that mothers nurse only their own young and that they have the ability to select their own young from a large group. When the mothers leave the roost at night to feed, the young are left behind clinging together in one or two large clusters, but during the day each young clings to its mother. Comparison of band numbers of mothers and their accompanying young on successive visits to the same nursery colony showed that in every case the mother was carrying the same young as on the previous visit; hence, whenever she had returned from feeding she must have selected from the cluster of young the same individual that she had left.

Habitat

Virginia 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 rear young in maternity caves, which are usually closer to food sources than hibernation caves, which are better protected from the cold and wind. Maternity colonies settle deep within the caves, far from the entrance.

Distribution

Most subspecies of Townsend's big-eared bat are found in the western United States from the Rocky Mountains to the Pacific Coast. The Virginia big-eared bat is an eastern subspecies that was once more abundant in the Appalachian Mountains in Virginia, West Virginia, North Carolina, and eastern Kentucky.

The Virginia big-eared bat occurs in decreased numbers throughout much of its historic range. The largest colonies are found in ten caves in Pendleton County and one cave (recently discovered) in Grant County, West Virginia. Four caves serve as both hibernation and maternity sites: Hoffman School, Minor Rexrode, Peacock, and Arbegast/Cave Hollow. Four others are primarily maternity caves: Cave Mountain, Sinnit/Thorn Mountain, Mystic, and School House. Smoke Hole and Hellhole caves also sheltered bats in the recent past. The total West Virginia population in 1987 was 8,000, based on a count of about 3,500 females, up almost one-third since 1983.

In June 1995, West Virginia Division of Natural Resources personnel monitored populations of the bat at 11 summer colony sites in West Virginia. The censuses resulted in a total population estimate in these colonies of 6,338 bats (mostly adult females), an increase of 2.5% over the 1994 population level. Colonies ranged in size from 122 to 1,350 bats. One new site for this species was discovered following reports of big-eared bats observed by cavers. In September, biologists set up a mist net at the entrance of the cave, which is located in Grant County, and captured nine bats in about 30 minutes. A year later, biologists took another census and found that the population remained stable in comparison to the 1995 level. The Grant County bat cave was discovered to be a bachelor colony during the summer, but may also be important as a breeding site. The number of bats using the cave more than doubled by early September, when the sex ratio of the bats was found to be nearly 1:1.

Three bat colonies are found in Lee County, Kentucky, the best-known being at Stillhouse Cave. As of 1982, this cave had a hibernating population of about 1,700 bats. A 1987 census showed a dramatic increase over this figure, rising by 900 individuals to a total of 2,600. This increase occurred even as the Endangered Indiana bat (Myotis sodalis ) experienced a 50 percent decline in that cave.

Virginia's single colony, numbering several hundred, uses Cassell Farm No. 2 Cave as a maternity site and Higgenbothams Cave as a hibernation cave. Both caves are in Tazewell County. A 1988 census showed this population to be stable.

Black Rock Cliffs Cave in Avery County, North Carolina, still supports that state's only colony, but numbers there have recently declined to about 20 bats.

Threats

Factors limiting Virginia big-eared bats are not all understood. Although loss of habitat is suspected, there are still a large number of apparently suitable caves within the range that remain unoccupied. Predation by raccoons, horned owls, and feral cats occurs, but is minimal. The most significant factor in the overall decline of the Virginia big-eared bat is probably increased human intrusion into bat caves. Bats aroused from hibernation too often use up fat reserves that cannot be replenished until spring, causing starvation. In the 1950s cave exploration first became popular, and many caves were disturbed so often that bat colonies died out. Formerly isolated areas in the vicinity of caves are now used for recreation, bringing humans and bats into closer and more frequent contact. Bats tend to abandon cave sites that are disturbed frequently.

Conservation and Recovery

Most cave entrances on public lands have been fenced or gated to discourage intruders, and this action has resulted in measurable population increases. The U.S. Fish and Wildlife Service (FWS) has sought the cooperation of landowners to allow gating and the posting of warning signs at cave entrances on private land. In the past, improperly constructed gates actually contributed to the problem by interfering with bat egress, but gate design has now been improved. Signs erected at cave entrances typically provide information on the life history of bats and describe the consequences of disturbing hibernation.

An annual census of Virginia big-eared bat maternity colonies, begun in 1983, has revealed population increases of at least 30% and continues to provide data to determine long-term population trends. Gates and fences installed by the FWS and the Forest Service and the cooperation of caving associations in complying with entry restrictions seem to be assisting this positive population trend.

Contacts

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

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035
http://northeast.fws.gov/

References

Barbour, R. W., and W. H. Davis. 1969. Bats of America. University Press of Kentucky, Lexington.

Rippy, C. L, and M. J. Harvey. 1965. "Notes on Plecotus townsendii virginianus in Kentucky." Journal of Mammalogy 46:499.

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.