Bats are one of the most common mammals at Jewel Cave National Monument. Thousands of bats, of nine species, take advantage of the monument's food, water and shelter. In the Black Hills, bats represent about 17% of all mammal species.
Five species of Myotis and one species of Corynorhinus use the limestone caves throughout the year. Males and females of these species use the various limestone caves during the warm months for day and night roosts and use Jewel Cave as a hibernaculum through the winter. In late spring, pregnant Myotis are found at the monument, forming nursery colonies in ponderosa pine snags, rock crevices, and sometimes, buildings. Many of these colonies change roosts on a daily basis.
These Myotis found a comfortable roost at the visitor center.
Several hundred Myotis and Corynorhinus hibernate within Jewel Cave during the colder months, accessing the cave through the historic entrance, locating themselves within 360 meters of the entrance. The 2005 bat count was higher than 2004. A total of 1,555 bats were counted. There are 1060 Corynorhinus, 493 Myotis, 1 suspected Eptesicus and 1 possible Pipistrellus hibernating in Jewel Cave this winter. Overall, 212 more bats were counted this year than last year.
Townsend's big-eared bats in Jewel Cave
Big brown bats, one the the most commonly found bats in the Black Hills, use Jewel Cave as a summer night roost. Although they remain in the Hills for the winter, they usually relocate away from the monument to hibernate in buildings and other caves.
Fair Weather Friends
Two species of bat reside at the monument only during the warm months. Hoary bats, which are the largest of the local bats, have a heavy coat of fur and roost high in the foliage of trees. Silver-haired bats take advantage of the high number of ponderosa pine snags to establish daytime roosts. They form nursery colonies in cavities created by woodpeckers and under loose, peeling bark. They prefer snags with a diameter of over 15 inches, and prefer areas with snag densities of at least one snag per 4 acres of forest. Jewel Cave National Monument has relatively high snag density compared to the surrounding forest because wood-gathering and firewood cutting are not allowed at the monument. When the weather turns cold, the hoary and silver-haired bats migrate to the southern United States and Mexico.
Unsolved Mystery
Jewel Cave supports one of the largest known hibernating colonies (over 700 members) of Townsend's big-eared bats in the West. C. townsendii are not known to migrate great distances, yet only one nursery colony has been located in the Southern Black Hills, despite intensive searches. C. townsendii seem to choose inaccessible caves (and presumably mines) for giving birth and raising young, and tend to choose sites which have little disturbance from humans. One pregnant female was located at one of the monument's water sources in 1989, suggesting a nursery colony nearby. Information leading to the location of additional nursery colonies could help protect this species.
Beneficial Predators
Vacationers and the local community (including farmers) benefit from the insect control provided by the monument bats. These insectivorous bats most often eat beetles, moths, flies, and mosquitoes. They also eat cockroaches, termites, crickets, katydids, cicadas, and night-flying ants. A single little brown Myotis can catch hundreds of mosquitoes in an hour. Cucumber and June beetles, stink bugs, leafhoppers, and cutworm and corn ear worm moths, all well-known pests, are just a few of the many insects known to be consumed by big brown bats. Big-eared bats are particularly adept at catching moths.
Bats at Risk
Bats are slow-growing and slow-reproducing mammals. On average, bats rear one young a year. Some bats do not begin reproducing until they are two or more years old. Bats can be long-lived (a little brown bat was documented at 36 years of age), but the average life span of a bat that reaches adulthood is ten years. Bats are a food source for owls, hawks, falcons, raccoons, domestic and feral cats, and snakes. A single feral cat can kill as many as 30-40 bats in a night.
Bats sometimes form large colonies, which makes them susceptible to disturbance and vandalism. A significant portion of a colony can be put at risk each time the colony is disturbed, especially in the winter when they are hibernating. Because of their reproductive and colony-forming characteristics, bats do not bounce back as quickly after significant disturbance. Humans can put the monument bats at risk by disturbing nursery colonies, and by disturbing hibernation colonies.
Homeowners who attempt to evict bats from nursery sites might cause the adult females to abandon their young before the young are capable of flying and capturing food. This can result in starvation and the loss of a generation of bats. To avoid affecting the colony, bat exclusion should be accomplished before the bats arrive, or after they leave the roosts in late summer. Homeowners should provide alternate bat roosting sites near their buildings before excluding bats.
During winter, many bats enter hibernation, a state characterized by a much lower metabolic rate and a body temperature near that of ambient air, and requiring an insulated, sheltered roosting site. Arousal of hibernating bats results in an increased metabolic rate. Numerous arousals exhaust a bat's energy reserves and might result in the bats lacking sufficient fat and water reserves to survive winter.
Why is Jewel Cave a good hibernaculum?
The historic area of Jewel Cave has many different levels and temperature ranges. It provides a variety of suitable roosting habitats for a diversity of species. For instance, Corynorhimus hang from walls and ceilings at relatively low levels, and are tolerant of climatic fluctuations, while M.thysanodes, M. volans, M. lucifugus and Eptesicus fuscus hibernate in large rooms in relatively warm and stable environments.
The gated entrance works for bats in two ways. The gate provides protection; the historic area of the cave is locked from September through May. The gate allows for bat-friendly air flow, which leads to bat-friendly temperatures and humidity within the cave.
Jewel Cave's airflow, which is a barometric wind, may work for bats in an additional way. Recent research indicates that some bats sense changes in barometric pressure, and use this information to determine the likelihood of insect availability. It's possible that the monument bats monitor changes in barometric pressure to determine whether they should leave the cave in search of food.
Will you see bats during your visit?
You might see bats if you are visiting during the warmer months, and in the evening. The monument bats hunt for insects, their only food source, during the evening and night hours. They have been seen flying over the visitor center parking lot, and entering and exiting Jewel Cave at the historic entrance. Look for bats emerging from ponderosa pine snags, as well.
Monument Bat List
Eptesicus fuscus (Big brown bat)
Lasionycteris noctivagans (Silver-haired bat)
Lasiurus cinereus (Hoary bat)
Myotis lucifugus (Little brown myotis)
Myotis volans (Long-legged myotis)
Myotis ciliolabrum (Western small-footed myotis)
Myotis septentrionalis (Northern myotis)
Myotis thysanodes pahasapensis (Black Hills fringed-tail myotis)
Corynorhinus townsendii (Townsend's big-eared bat)
Several of these species have been given special designations. Four species have been designated US Fish and Wildlife Service "species of concern": M.thysanodes, M.volans, M.ciliolabrum and C.townsendii. Four species are monitored by the South Dakota Natural Heritage Program: M. thysanodes pahasapensis, L. noctivagans, M. septentrionalis, and C.townsendii.
For additional information on bats, contact:
Bat Conservation International, PO Box 162603, Austin, TX 78716 (512)- 327- 9721 or http://www.batcon.org
Last updated November 9, 2003
e-mail jeca_interpretation@nps.gov