The report last week that white-nose syndrome has been identified among bats in three more Tennessee caves is only the latest sign that the state's bat population is in grave peril.
"The question is, is it going to lead to total extinction," says Gary McCracken, head of the University of Tennessee's Department of Ecology and Evolutionary Biology, "or will there be some survival?"
"Right now," he adds, "it's looking like total extinction."
The syndrome is apparently caused by a fungus, Geomyces destructans, that grows in white speckles on bats' faces and bodies. Since it was first observed in upstate New York just four years ago, it has spread through bat colonies up and down the Appalachians. Federal wildlife officials say it has already killed more than a million bats.
The exact mechanism of the syndrome's fatality is still being studied, but McCracken says the key elements are that the fungus spreads easily and it likes cold temperatures. As a result, it is at its most active during the months that bats are at their most vulnerable: during hibernation.
"It is really pretty insidious," McCracken says. "When the bats go into hibernation, their immune systems shut down." The fungus invades the bats' skin, and by forcing the animals to use their scarce energy reserves to try to fight it off, it apparently weakens them to the point of starvation. Bats with white-nose syndrome have been seen flying during the winter, when there is nothing for them to eat, out of either confusion or desperation.
The fungus has been traced to Europe, McCracken says, where it has been seen among bats—but for reasons not yet understood, it has not been fatal. European bats may have evolved some biological defenses against it. It was most likely introduced to the United States via human transport. McCracken says a tourist might have brought traces of the fungus to America on shoes or clothing and then ventured into a commercial cave somewhere in the Northeast.
It has been found in most of the common bat species, including little brown bats and Indiana bats. "We haven't yet documented the fungus on tree bats," McCracken says, and those species might be less likely to be exposed to it. But, he adds, there is little reason to think they will ultimately be immune.
Scientists and wildlife officials have watched with mounting alarm as the syndrome has traveled north to Vermont and Canada and south through the Virginias and now into Tennessee. The first cases here were confirmed in February by the Tennessee Wildlife Resources Agency, at Worley's Cave in Sullivan County. Since then, it has been found at Dunbar Cave in Montgomery County; at White Oak Blowhole cave in the Great Smoky Mountains National Park (site of Tennessee's largest known population of Indiana bats); and, just last week, at caves in Carter, Fentress, and Van Buren counties.
Multiple studies of the syndrome and its effects are under way in state and federal agencies, but so far officials have few means of containing it and no way to treat affected animals. George Wyckoff, an ecologist who is chairman of TWRA's Tennessee Bat Working Group, says, "Really, the only thing we're able to do is close caves." The hope is that keeping people out of caves will reduce the chances of human transmission of the fungus from one bat colony to another. But at this point, Wyckoff acknowledges, most of the spread is happening from bat to bat.
Private caving groups are also cooperating. The Southeastern Cave Conservancy, Inc., which owns or leases 27 preserves with 63 caves across six states, has closed all of its caves with significant bat populations and issued stringent new cave visitation guidelines. The guidelines call for complete cleaning and decontamination of all clothing and equipment before and after any cave visit.
"Cavers are taking this issue very seriously," says Brian Krebs, CEO of the Southeastern Cave Conservancy. "We are trying our very best to find a good mix of use and conservation." Krebs notes that caving groups have in the past helped bat colonies recover, by controlling access and reducing the vandalism that caves are often targets for.
Wyckoff says research has begun on anti-fungal agents that could theoretically be used to treat bats. There has also been some discussion of culling affected colonies, but there is little enthusiasm for the idea: "Nobody really wants to think about purposely decreasing the population," Wyckoff says.
It won't be clear for at least a year whether Tennessee will see the kind of mass die-offs that have followed white-nose syndrome everywhere else it has been found. But if it happens, Wyckoff says humans will be affected, too. "Bats are the primary predators of night-flying insects," he says. Fewer bats would mean more mosquitoes and more crop pests, and therefore probably greater dependence on pesticides.
The scale of the threat here is significant. Tennessee has more caves than any other state, and some of the largest known gray-bat colonies. Wyckoff says Hubbard's Cave in Warren County alone is home to more than 500,000 gray bats.
Overall, he says, "We're talking about the loss of potentially millions of animals."