Going to Bat for BATS 


Long misunderstood, bats still rank among the least-studied and least-loved animals. But thanks to the efforts of Bat Conservation International along with the National Park Service, bats are gradually gaining more respect.

   WHAT DO limestone passages in Carlsbad Caverns and within the Mammoth Cave system, abandoned mines in the Great Smokies, and rainforests in American Samoa have in common? In addition to being managed by the National Park Service, these diverse habitats all host bat maternity colonies.

   Worldwide, bats account for about one-quarter of all mammal species. But with nearly a thousand types identified, bats still rank among the least-studied and least-loved animals. Dr. Merlin Tuttle, founder of Bat Conservation International (BCI), is out to change that. BCI promotes bat research and protection, and largely through partnerships with federal agencies such as the National Park Service—which is also committed to biodiversity and the essential role bats play in ecosystems—bats are gradually gaining more respect.

   Myths and superstitions often mask the truth that bats are clean, intelligent, and beneficial. The little brown bat, a common species in much of North America, can devour 600 mosquitoes per hour. Long-nosed bats of the Southwest pollinate and disperse seeds of important plants including agave and organ pipe and saguaro cacti. In American Samoa, a third of the tropical tree species depend upon bats for pollination or seed dispersal. Bats also pollinate bananas, avocados, dates, figs, mangos, and cashews, and their contribution to commercial agriculture through natural insect control is worth millions of dollars annually.

   Among the 45 species of bats native to the United States, six are endangered, and several more are proposed for protection. Tuttle says, "Bats suffer from habitat loss and environmental pollution, but the primary cause of their decline is destruction by humans acting out of fear and ignorance." Some bats gather in large maternity colonies or hibernate together in winter, and these assemblies are especially vulnerable to disturbance. Bats reproduce so slowly—usually only one pup per female per year—that when a colony is vandalized, it may not recover.

   About 60 sites within the National Park System have caves that provide essential living space for bats. In 1995 BCI and the National Park Service (NPS) signed a memorandum of understanding to develop bat conservation, research, and educational projects. Since then, BCI experts have participated in many bat population surveys and provided technical expertise for such improvements as bat-friendly cave gates.

   At Mammoth Cave National Park in central Kentucky, bat-friendly cave gates have started to rectify a problem that began decades ago when the cave was mined for nitrates and became a tourist attraction.

   Discovered by colonists in the 1790s, Mammoth Cave's bat guano-enriched sediments provided a valuable source of nitrate, tons of which were removed for use in gunpowder for the War of 1812. About that time, sightseers began touring the cave. An 1810 newspaper article refers to bats being "crowded so close that they resembled a continued black cloud." When Yale biologist Benjamin Silliman, Jr., visited in 1850, he estimated them by the millions.
But by June 1996, when park researchers invited BCI's Tuttle to accompany them into Mammoth Cave, evidence was scarce. On cave walls and ceilings, scientists discovered reddish marks where roosting bats had stained the rock. Scientists also found and dated remains in many parts of the cave.

   Analysis of bones indicated primary use by hibernating Indiana bats, with some gray bat summer roosts in warmer rooms. Using a formula of 300 Indiana bats per square foot of roosting space, researchers estimated that as many as 20 million Indiana bats could have used these passages in the past.

   According to Tuttle, Mammoth Cave was once possibly the world's largest and most important Indiana bat hibernation site.

   Mammoth's relationship with Indiana bats is especially important because they, along with gray bats, are endangered. This status means that they are accorded special protection under laws enforced by the U.S. Fish & Wildlife Service (USFWS) and ensures that habitats used by these animals receive protection. Areas occupied by the endangered species may also be seasonally or permanently closed to visitors to prevent disturbance.

   USFWS surveys in 1993 showed that Indiana bat populations nationwide had declined 41 percent during the previous decade. Indiana bats inhabit riparian forests in New England and the Midwest in summer, then in winter they seek caves with stable temperatures between 37 and 45 degrees Fahrenheit. Individuals often rest in the same place on the same cave wall winter after winter. Most Indiana bat hibernacula are located in Kentucky, Missouri, and Indiana, where only 3 percent of all caves provide suitable conditions. About 85 percent of the Indiana bat population now winters in just seven caves, several of which are located within Mammoth Cave National Park.

   About 350 miles of passages at Mammoth have thus far been mapped. As recently as 1947, Long Cave—one of those caves—sheltered more than 50,000 wintering Indiana bats. But when a concrete wall and heavy entrance door were installed there 35 years ago to prevent vandalism, temperatures rose and bat use declined. Five years ago, at the urging of BCI and the USFWS, park managers designed and installed bat-friendly gates at the entrances of Long as well as Dixon, Colossal, and Bat caves. Since then, the wintering populations have increased. Long Cave now hosts about 650 Indiana and 400 gray bats in the winter. Colossal, which lost 95 percent of its Indiana bats between 1950 and 1995, now shelters about 350 of the animals in the winter. Dixon Cave, near Mammoth's historic entrance, hosts a fairly stable winter population of 5,500 Indiana and 500 gray bats.

   Although Indiana bats do not presently hibernate within Mammoth Cave itself, park ecologist Rick Olson expects they will return in time. Originally the cave had a cool, moist, stable environment. It "breathed" in winter when cold air poured in at lower levels and air warmed by interior walls escaped from higher openings. When large sheets of metal were seasonally placed over the entrance to keep winter tourists warmer, temperatures in passages formerly occupied by hibernating bats increased above their tolerance.

   Now, park employees have installed a USFWS-approved gate that allows bats to pass easily while significantly restoring the historic air flow. A network of cave atmospheric monitoring stations collects data to gauge progress of the environmental restoration effort. Because biologists know what temperature range Indiana bats need to survive in hibernation, they have a target for fine-tuning the gates until this microclimate is duplicated.

   In hopes that a quieter scene will entice bats to return, winter tours in part of Audubon Avenue have been discontinued. Outside near the cave entrance, signs discourage visitors from disrupting bats.

   "Our main goals," says Olson, "are to restore bat habitat and minimize disturbance. We don't really know how Indiana bats discover places to hibernate, but we have been encouraged by three new sightings." 

   Three bats are a far cry from the millions that once roosted here, but their presence is a very positive sign. The park, Olson says, hopes to emulate the success of Wyandott Cave in southern Indiana, where Indiana bat populations are increasing, even though winter tours of the cave continue.

   Carlsbad Caverns National Park in southeast New Mexico is host to 15 species of bats, including the famous summer colony of Mexican free-tailed bats. Each summer 70,000 to 80,000 visitors watch the evening spectacle of Carlsbad's bat outflight while interpreters talk about the animals' key role in the ecosystem. These insectivorous bats migrate to Mexico for the winter. Park scientists are examining the foraging range and diet of the summer colony, determining population trends through infrared photography of the roost, and investigating the status and condition of winter roost sites in Mexico.

   Bat populations at Carlsbad declined during the middle of the last century, in part, because of poisoning from DDT, a widely used agricultural pesticide that accumulated in the bats' brain and body tissues. Although the use of DDT has been banned in the United States and Mexico, soil residues from this long-lived chemical and the current use of other insecticides may still pose a threat to bat populations in the Southwest.

   Before 1981, shafts drilled to facilitate guano mining at Carlsbad Caverns made the cave unacceptable to millions of Mexican free-tailed bats that formerly lived there. Then, the National Park Service sealed the shafts, providing better habitat for the remaining 250,000 bats. Recent infrared photo-censuses show 300,000 to 500,000 free-tailed bats now roost there each summer.
Although caves are among the most common habitat for bats, the animals also roost in trees and other structures. One type of structure, abandoned mines, has provided an unexpected housing bonanza for bats.

   According to the NPS Geologic Resources Division, more than 10,000 abandoned mines are scattered throughout the National Park System. Sheryl Ducommon, director of BCI's North American Bats and Mines project, believes that 10 to 15 percent of these receive substantial bat use.

   In the past, mines were often sealed without consideration for wildlife. Now, Ducommon and BCI's Dan Taylor visit several parks annually to assist with mine surveys.

   "Western parks are under tremendous pressure," says Ducommon. "They have hundreds of mines with safety and bat concerns." Since 1994, BCI has offered nearly 20 regional Bats and Mines Workshops to train employees with federal and state agencies how to safely assess these situations.

   Noteworthy mines in Organ Pipe Cactus National Monument and Coronado National Memorial, both in Arizona, safeguard lesser long-nosed bats. These endangered bats feed on the nectar and fruit of saguaro cactus in late spring at Organ Pipe, where there is a maternity colony of 8,000 to 15,000 females. Some 3,000 to 30,000 long-nosed bats visit Coronado in late summer to feed on agave nectar.

   At Big Bend National Park, Texas, where the hazard-filled Mariscal mercury mine descends 450 feet underground, Ducommon surveyed a Townsend's big-eared bat maternity roost there that shelters about 10,000 bats—making it the largest big-eared bat maternity colony in the United States. BCI also consulted on the ten gates that maintain good air flow and bat access while securing the mine from visitors, as well as providing interpretive signs outside the mine.

   Wildlife biologist Raymond Skiles is delighted with the attention being given to bats at Big Bend. Scientists from the University of Texas have recently identified the yellow bat as a new species for the park and the state. The USFWS is also funding an international study of the Mexican long-nosed bat with Dr. Arnulfo Moreno. "These bats were listed as endangered in late 1980s, but this is the first true look at the bat on a range-wide basis," Skiles states. "We are now shining a long-needed spotlight on a group of animals that has been neglected."

   More good bat news is emanating from other NPS sites. The largest hibernating colony of gray bats west of the Mississippi River uses Bonanza Cave near the boundary of Ozark National Forest and Buffalo National River. Bonanza shelters 250,000 gray bats annually, roughly 15 percent of the known population. Cave Mountain Cave normally hosts 100,000 wintering gray bats, but last year 160,000 to 200,000 individuals hibernated there. Geologist Chuck Bitting says, "Gray bats are responding favorably to protection. Maternity colonies seem to be doing well, with slightly more bats counted each summer."

   In addition, big-eared bats have moved into talus caves at Pinnacles National Monument in California. In response, managers closed the area to safeguard the bats and wrote a concise bat management plan, now a prototype for other parks. At Joshua Tree National Park, mine surveys have protected California leaf-nosed bats, and similar work at Death Valley National Park has secured Townsend's big-eared bat maternity roosts and the largest hibernaculum known in the California desert. With BCI matching funding and technical assistance, a cave at Grand Canyon that once sheltered Arizona's most productive big-eared bat nursery has been gated. After years of absence, more than a hundred big-eared bats and four other species have returned. Finally, at Great Smoky Mountains, planning is under way to protect a maternity roost and the hibernaculum of the largest known colony of eastern big-eared bats.

   "Bats are among the most gentle, beneficial, and necessary animals on earth," BCI founder Merlin Tuttle summarizes. "Wherever bats are found, they are essential elements in nature's delicate web of life." With BCI and NPS working together, the outlook for the protection of bats and their ecosystems in the 21st century is considerably more positive than it was a hundred years ago.