This Halloween, forget the image of bats as bloodthirsty vampires from the underworld. A species of these flying mammals - the furry-faced Indiana bat, equal in weight to three pennies - faces a reality much more frightening: the threat of extinction.
The Indiana bat, found throughout the eastern states, is estimated to have numbered in the tens of millions in and around Kentucky's Mammoth Cave National Park before farming, urban development, and deadly tree diseases took a toll on the animal's habitat and food sources. Since 1967, when the bats were added to the federal endangered species list, their numbers have declined by more than 60 percent, with a current national population of about 330,000.
"What's perceived by bat biologists is that this decline is due to a shortage of maternity habitat," says Mark DePoy, Mammoth Cave's chief of science and resource management.
Over the decades, the bats have lost old growth forest that they prefer for nesting-a challenge for animals that bear one offspring each year-along with food sources, foraging space, and hibernation sites. Scientists estimate that at one time as many as ten million bats wintered in Mammoth Cave, a number that has dropped to zero. And while Indiana bats currently use five other caves in the park as hibernation sites, they are sparsely occupied.
A variety of factors have caused these losses. They range from human-made changes to Mammoth Cave itself, to the loss of American chestnut and elm trees as a result of disease and blight, to the high levels of mercury from nearby coal-burning power plants.
Before Mammoth Cave was established as a national park in 1941, much of its 52,000-plus acres was grazed, farmed, or exploited for timber harvest. In addition, Dutch elm disease killed 90 percent of the nation's American elm trees-a species the Indiana bat depended on to raise its young. Today, the woodlands that replaced the elm are too young for roosting females.
Food sources may have dwindled when the American chestnut fell victim to blight in the 1930s and '40s. The trees bloomed in mid- to late-June when few other plants were blossoming, and scientists believe the pollen lured nectar-loving insects, providing abundant prey for the Indiana bat. The bats' foraging grounds were also affected. At one time, DePoy says, Kentucky had two million acres of tallgrass prairie known as the Penny Royal Plateau-all but 1,200 acres of which have been plowed.
Another major food source - aquatic insects such as dragonflies and may flies - is contaminated with mercury. One bat can eat the equivalent of one-half to three-fourths of its weight in insects each day. Mercury builds up in the bats, which can live to be 20, compromising their health and making them more susceptible to other stressors, such as disease, drought, and disturbances during hibernation.
Several decades ago, the Indiana bats' hibernating population in Mammoth Cave dipped drastically, decreasing by the millions. When scientists looked for causes, they realized a solid cement staircase built in the 1950s had restricted ventilation, reducing the cold winter airflows. "We realized that the cave was too warm in the winter," DePoy says. "Indiana bats prefer anywhere from 4 to 8 degrees Celsius for hibernating-now the cave averages 11 degrees Celsius."
But a number of steps are being taken to aid the bats. DePoy and his colleagues have replaced the cement stairs in Mammoth Cave with metal grating to allow more airflow. "We're hoping it restores the average winter temperature needed for hibernation," he says. His team will scout out other caves for potential hibernation sites and post signs to warn visitors away from sensitive habitat.
Bat Conservation International, a major force in the research and recovery efforts of threatened and endangered bat species, has been involved at Mammoth Cave with the construction of an artificial bat housing structure where the animals can raise young. And a research project in the park, created in partnership with the Kentucky Department of Fish and Wildlife Resources, concentrates on identifying nesting sites by capturing lactating females and tracking them using radio transmitters.
"We want to identify areas of the park that are heavily used for nesting to make sure there's no development, like trails and campsites," DePoy says. "We need to keep people away so those places remain quiet and secluded. This should help the recruitment process of bats."
Two other projects may aid the bats: restoration of original grasslands in Kentucky and a breeding program to produce disease-resistant strains of American elm and chestnut trees. DePoy and his team are removing exotic vegetation and replanting tallgrass prairie species on 120 acres within the park.
"The only remaining obstacle," DePoy says, "is to find a way to attenuate the high levels of mercury in the park's environment derived from burning large quantities of coal."
