Denizens of the dark.
It is a chilly winter day in the Arkansas Ozarks. A battered car stops along a gravel road above the head waters of Buffalo National River, and five scruffy occupants walk a few paces into the woods. They glance nervously at a sign on a chain-link fence warning that endangered gray bats are hibernating nearby. One of the men pats a bulge under his black leather jacket and says, "If any of them bats fly in my hair, I'll blow 'em away."
"Come on man," urges another, puffing a small bag of marijuana from his vest. "Let's go." They scale the fence and disappear into a cave.
Some 1,500 miles away in southwestern Mexico, a farmer and his son pile sticks and brush at the entrance to a cavern. They light the stack and watch in satisfaction as dense smoke billows into the darkness. "This will kill the vampires," the old man proclaims. He has no idea that the small brown mammals roosting in the cave are actually lesser long-nosed bats. These endangered creatures feed on flower nectar and fruit.
Not far away, phosphate miners gather outside a cave where they have been harvesting guano (bat droppings) for the past few months. Hoards of bats have returned and are clinging to the ceiling above the guano deposit. The men are superstitious and afraid to enter; yet, to earn their meager living, they must continue mining.
Another man arrives. His burro is laden with old tires, and he carries a small container of gasoline. Within minutes, acrid black smoke rolls into the cave. Not only will the fumes trap and kill the bats, but toxic residue from the tires will probably discourage future populations of Mexican free-tailed bats from roosting there.
These scenarios reveal a few of the hazards facing bats that spend a portion of their lives in national parks. Unlike many mammals that remain near the spot where they were born, bats can fly. Their annual cycles take them to various habitats and, at many of these places, protection is not guaranteed.
Throughout folklore, bats have been portrayed as sinister, disease-bearing vampires. Actually, bats are victims of prejudice and misinformation. Only three species, all of which five in Latin America, dine on blood. Vampire bats can be a nuisance to cattle, but even worse, their feeding habits have given more than 900 other species of bats a bad reputation.
In a survey of animal "likability" cited by Bat Conservation International (BCI), a friends-of-bats organization based in Austin, Texas, bats scored near the bottom, along with vultures, roaches, and rattlesnakes. In truth, bats are well-groomed, intelligent, and beneficial. Nearly 30 percent of the world's bats eat nectar or fruit. They pollinate a long fist of foods including bananas, figs, dates, and cashews. The remaining 70 percent eat insects, consuming more than one-third of their body weight in flying ants, beetles, and moths each night. Among all of these insects are a large variety of agricultural pests, including moths and beetles that cost American farmers and foresters millions of dollars annually. Only recently have we begun to understand bats' ecological importance.
Free-tailed bats migrate from Mexico into the southwestern United States each spring. They congregate in caves in New Mexico, Arizona, Texas, and Oklahoma, and females gather in a few large maternity colonies. The swirling funnel of free-tailed bats exiting Carlsbad Cavern drew attention to this cave in eastern New Mexico nearly a century ago, but the huge pile of guano they deposited was initially more prized than the animals. Some 100,000 tons of the ammonia-rich substance was mined for use as fertilizer between 1903 and 1923. To facilitate the mining operation, two shafts were blasted through the ceiling of Bat Cave passage, where millions of pregnant Mexican free-tailed bats gathered each year to raise their young.
The body heat from tens of thousands of bats increases cave ceiling temperatures to levels at which babies can survive while their mothers are away feeding. When mine shafts penetrated Carlsbad's nursery, heat vented from the cave. Although no good records exist, many bats may have abandoned Carlsbad after it was punctured. Others formed smaller nurseries elsewhere in the passage.
Whether the bats left immediately is difficult to verify, but ample evidence demonstrates that puncturing the cave chased the animals away over a period of 50 years. In 1936, more than a decade after the Park Service acquired Carlsbad, the maternity colony contained about 8.7 million bats. By 1956, their numbers had dropped to 3 million, and by 1973, a mere 218,000. Finally, in 1981 park officials plugged both mine shafts. Four years later, female bats began to roost in the original nursery. Subsequently, the size of the maternity colony at Carlsbad has increased to about 750,000 free-tails.
Mammoth Cave in central Kentucky also has a sad history of insensitivity to bats. Tourists have flocked to Mammoth and nearby caves for 150 years. Lights and visitor noise make show caves unsuitable for bats, which require consistently dark, quiet areas to raise young or hibernate. Visitor comfort has at times overshadowed the needs of cave fauna. For many years, large sheets of metal at Mammoth's historic entrance shielded tourists from the natural rush of cold air feeding the cave. Hibernating bats need relatively cold temperatures. Before NPS acquisition, a roost of the rare Indiana bat at Dixon Cave, which is at the park but not part of Mammoth Cave, was fenced with chicken wire to keep bats out. Barriers were erected at other entrances to control visitors.
"Mammoth Cave was one of the biggest abusers of bats for years, and it had some of the world's worst gates,' relates Roy Powers, assistant professor of engineering technology at Mountain Empire Community College in western Virginia. Powers has installed secure, bat-friendly gates at nearly a hundred caves and mines on federal, state, and private land. These gates keep intruders out with horizontal bars that still allow the bats to enter and exit the cave unhindered. In 1994, Powers was a consultant on a project to improve Mammoth Cave's gates.
Robert Currie, a U.S. Fish and Wildlife Service biologist responsible for monitoring endangered bats in Kentucky, Tennessee, and the Carolinas, agrees that the park's bats were not always a priority. Long Cave, another cave at Mammoth, sheltered more than 50,000 wintering Indiana bats in 1947. It had a poorly designed gate and concrete wall. The small opening allowed predators, such as snakes or raccoons, to grab bats as they entered or exited. (Owls and other raptors also prey on bats.) Impaired airflow changed humidity and warmed the cave above the range preferred by hibernating Indiana bats. Currie located only 782 of the nowendangered species in this hibernaculum on his 1993 census. "This represents less than 2 percent of the historic population in Long Cave," he says.
"The poorly designed gate and wall were replaced last summer," Currie continues. "Normal temperatures and airflows have apparently been restored to Long Cave, and we expect the Indiana bat population can begin to recover.' But for mammals that have only one pup a year, recovery will not be rapid. According to Mammoth Cave resource management specialist Rick Olson, several other caves where Indiana bats overwinter will soon receive better bat gates.
In summer insect-eating bats find abundant food over rivers, streams, marshes, and lakes. Like Neotropical songbirds, some migrate to Mexico and Central America for the winter. Others, including big-eared bats, hibernate. In caves with constantly cool temperatures, their breathing and heart rates slow, allowing them to survive on reserves of stored fat. If they are disturbed during hibernation, the arousal process burns precious calories. Repeated intrusions cause starvation.
Endangered gray and Virginia big-eared bats are responding positively to protection of winter roosts. The Virginia big-eared bat populations dwindled to about 1,300 individuals by 1979. Recent counts in their central Appalachian range indicate a tenfold increase.
Scientists are cautious, though, because pesticides used to control the gypsy moth caterpillar (an exotic species that defoliates hardwoods) also kill the larvae of native moths relished by big-eared bats. Endangered Ozark big-eared bats are known from only two maternity caves in Arkansas. Recent spraying for gypsy moth caterpillars in the Buffalo River watershed, which is undoubtedly used by these bats, is a concern. Great Smoky Mountains National Park hosts significant numbers of hibernating Rafinesque's big-eared bats in remote abandoned mines. Summer roosts for these bats, under evaluation for the endangered species list, are located in old buildings at Mammoth Cave.
About 95 percent of the nation's gray bats overwinter in several caves scattered across Missouri, Tennessee, Kentucky, Alabama, and Arkansas. Dr. Michael J. Harvey, chairman of the department of biology at Tennessee Technological University, has studied bats in this region since the late 1970s. He monitors several caves at Buffalo National River used by gray and Indiana bats. A sizeable colony of gray bats (about 15 percent of the national population) hibernates in a U.S. Forest Service cave near Buffalo River. Harvey's censuses show gray bat numbers are stable or increasing slightly. Secure gates, in place for more than a decade at Buffalo River, help prevent excessive human intrusion.
Harvey is worried about steadily declining Indiana bat populations. Gray bats move from winter hibernation caves to separate summer nursery caves. Indiana bats winter in caves but select forested streamside or floodplain locations for maternity colonies. Nurseries are located in trees under large flaps of bark.
A Canadian study using radio telemetry determined that old-growth forests are vital to certain types of bats. Harvey believes dwindling habitat may be hampering reproduction of Indiana bats, but so far he has secured no funding for a thorough study. Unlike bears or deer - which often garner dollars for popular research projects-bats, shrews, and other "unloved" creatures are underfunded for research.
Raymond Skiles, a wildlife resource management specialist at Big Bend, echoed that frustration. "The biggest challenge is to get adequate baseline data," he said. "At Big Bend, we don't have a cave inventory or a bat inventory. Periodically, researchers with an interest in one or more species document them on their own. For a number of bat species, we can say if they're here or not, but to comment on the overall health of bats in the park requires more than an occasional sample."
Of special interest at Big Bend is the Mexican long-nosed bat, an endangered species recorded from only this and one other location in the United States. Adult females reproduce in Mexico, then bring their pups north to feed on century plant nectar. They depend on a single roosting cave in the park.
Organ Pipe Cactus National Monument, in southern Arizona, hosts the largest maternity colony of endangered lesser long-nosed bats in the country. Another maternity colony was located near Saguaro National Park until the private cave was opened to tourists some years ago. Migrant lesser long-nosed bats still visit Saguaro in the summer. They are important pollinators of organ pipe and saguaro cacti, whose fruits provide food for the bats. The bats, in turn, spread seeds for new cacti in their droppings.
Several other Western parks have sizeable bat nurseries. In 1985 a mixed maternity colony of Mexican free-tailed and Yuma myotis bats moved into a cliffside cave above the main ruins at Bandelier National Monument in New Mexico. Park managers rerouted a trail slightly to alleviate problems from debris and guano raining down on visitors. Neither bats nor visitors seemed inconvenienced by the arrangement, and the colony is flourishing. A trailside colony of about 9,000 Mexican free-tailed bats inhabits El Malpais National Monument in New Mexico. Although posted with interpretive signs, the fairly accessible cave experiences intrusion problems from illegal campers. A remote cave at Lava Beds National Monument in California shelters a seemingly stable population of 345,000 Mexican free-tails. Heavy pesticide use on an adjoining wildlife refuge where the bats feed concerns park officials.
Bats face multiple problems that cross national boundaries, according to Merlin Tuttle, executive director of BCI. The most serious problem is decreasing habitat. BCI is pioneering agreements with federal, state, and private agencies to protect important bat roosts in caves, mines, and forest habitats.
In January, BCI and the Park Service signed a memorandum of understanding, allowing the two groups to conduct cooperative studies on bats. BCI can also support the Park Service in seeking funding for studies, inventories, and other research. BCI officials see an opportunity to engage in projects with NPS at four park units in particular: Chesapeake and Ohio Canal National Historical Park in Maryland, Chiricahua National Monument in Arizona, Death Valley National Monument in California, and Big Bend National Park in Texas.
Besides research, education is a vital component in any attempt to aid bats. Two recent meetings between U.S. and Mexican officials have emphasized the need to educate Latin Americans about vital bat overwintering areas. Pesticides also threaten bats by reducing the general prey base and, in some cases, by poisoning individuals.
Are we taking appropriate action to protect bats? According to Tuttle, "More than 50 percent of American bat species are in severe decline or already listed as endangered. Bats are exceptionally vulnerable to extinction, in part because, for their size, they are the slowest reproducing mammals on Earth."
As we learn more about the key roles bats play in the health of various ecosystems, we must redouble our efforts to provide secure refuges for these highly specialized creatures of the dark.
The Benefits of Bats
Realizing the beneficial aspects of bats, a growing number of North Americans are attempting to lure them into their yards by putting up bat roosting boxes. Organic farmer Tony Koch was troubled with corn earworm larvae dining on his sweet corn. Since he attracted approximately 2,000 little brown bats to bat houses on his Oregon farm, the ear-worms have disappeared.
That does not surprise Merlin Tuttle, director of Bat Conservation international. "One female Heliothis moth [an adult earworm] can lay up to 100,000 eggs," he explained, "and the larvae are tremendous pests on corn, tomatoes, and other crops." But little brown and big brown bats relish Heliothis moths, keeping the pests in check. "We also know that a single little brown bat can catch 600 mosquito-size insects in an hour," Tuttle added. A colony of 150 big brown bats-a number that could easily fit in a residential bat roost - will consume a quarter-million leafhoppers, cucumber beetles, stinkbugs, and June bugs during one summer.
Unlike cavity-seeking bluebirds or tree swallows, which readily accept many styles of nest boxes, bats are more finicky. "There are nearly a dozen species in North America that use bat houses," Dr. Tuttle said, "but they all have different requirements for crevice widths, depth of the box, roosting temperatures, and nearness to trees."
Solar exposure is an important variable. "It is rare in Canada to have a successful house that's not black and in all-day sun. In Pennsylvania," Tuttle continues, "a black box could be successful in six to seven hours of sun. In the southern United States, a black box would be too hot, unless it is always shaded." Tuttle suggested that anyone serious about attracting bats should obtain BCI's The Bat House Builder's Handbook. It includes several basic designs and mounting options to attract bats in various regions.
For proof of bat house success, one need look no farther than Mineral Wells, Texas. In 1988 resident Amanda Lollar found an injured Mexican free-tailed bat and nursed it back to health. She became fascinated with the creature and organized BATS, the Beneficial Animal Teaching Society, for bat rehabilitation and education. Once considered a nuisiance - the bats would sometimes gather in walls, loose window sills, or attics of old buildings - the animals are now provided roosts by the townspeople.
By the summer of 1994, two dozen bat roosts graced the downtown area, and two-thirds have been accepted by bats. Visitors to Mineral Wells can pick up a map at BATS headquarters for a walking tour of the town's roosts.
For more information on BATS, send a self-addressed stamped envelope to: Amanda Lollar, 217 N. Oak, Mineral Wells, TX 76067.
For a copy of The Bat House Builder's Handbook and other educational material about bats, send a donation to: Bat Conservation international, P.O. Box 162603, Austin, TX 78116.
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|Title Annotation:||changed attitudes towards bats; includes a related article|
|Date:||Mar 1, 1995|
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