The cave near the western shore of Lake George in the town of Hague has long been one of the biggest winter homes to little brown bats in North America.

A count of bats in the mid-1990s led to the conclusion that 185,000 of the tiny mammals hibernated there, and state wildlife officials believe that number likely topped 200,000 a few years later.

Last winter, when biologists from the state Department of Environmental Conservation visited the cave, they concluded there were somewhere between 2,000 and 3,000 left, said Alan Hicks, a DEC wildlife biologist.

Another cave near Paradox Lake in Essex County has been similarly devastated by a mysterious disease that kills the bats as they hibernate during the winter.

"There's not a (bat) population in the Adirondacks that hasn't been affected," said Alan Hicks, a DEC wildlife biologist who is heading the state's efforts to investigate. "I'm not looking forward to this winter."

The culprit is a mysterious malady dubbed "white nose syndrome," which has devastated bat populations across the Northeast the past two winters, to the point where some hibernacula have lost 95 percent of their bats.

Bats that become infected awaken during their hibernation, apparently because of the discomfort caused by a non-native fungal infection that leaves a white coating on their faces. They seem to die of starvation after they burn through body weight and can't find food to replenish.

"They seem to exhaust their energy reserves prematurely," said Joseph Okoniewski, a DEC biologist with the agency's pathology unit.

The caves of the southeastern Adirondacks and Capital District are at the epicenter of the outbreak, a catastrophe that has spread as far south and west as West Virginia over the past 18 months.

It's been called the most precipitous decline of a species on record, and answers about how to stop it are few and far between.

"It's heartbreaking," said Mylea Bayless, a conservation biologist with Bat Conservation International, a nonprofit advocacy group. "I don't think people truly understand the impact this is going to have on our communities and our environment."

Bats do more than hang in our home attics and flit above our heads at night.

They are a crucial part of the food chain, eating up to half their weight in bugs a night. One of their main foods in the Northeast is mosquitoes, a pest that spreads numerous diseases to mammals.

"They eat a lot of bugs, and some of these bugs are a problem for us," Hicks said.

Wiped out

It was the winter of 2006 when cave explorers working their way through Howe's Caverns, southwest of Albany, noticed irregular activity among bats there.

The winged creatures should hibernate in the winter, but some were found to be awake and covered with a white fuzz. The issue seemed isolated, so scientists initially thought little of it.

During the winter of 2007, though, the problem returned, and more bats were found dead there.

By the winter of 2008, tens of thousands of bats in caves and mines around upstate New York were dying when they should have been safely in hibernation, and the malady had spread to Vermont.

Last winter, the problem worsened.

Wildlife biologists from New York and Vermont spent countless hours this summer surveying caves and mines where bats spend their summers, and the drop in bat numbers has been sobering.

Populations of little brown bats around the Adirondacks are off by 95 percent in some caves and mines, Hicks said. Little browns are the small bats most people see at night, skimming the surface of ponds and lakes eating bugs.

One cave in Hague has long been the largest wintering site on the continent for little browns, and as of last winter, just a couple of thousand were left.

During a survey last month at a cave in Dorset, Vt., just minutes from the New York border, one bat was caught in three hours. During the same survey two years earlier at the same cave, 900 were caught in three hours, said Scott Darling, a Vermont wildlife biologist.

"That cave was kind of the poster child for us," Darling said. "The news we continue to get is not promising."

In addition to little brown bats, endangered Indiana bats seem most susceptible to white nose syndrome. For some reason, though, big brown bats have not been affected at rates the others have, Hicks said. Their numbers have dropped about 50 percent or so from it.

Mystery fungus

Little is known about how the fungus, dubbed geomyces destructans, made its way to the U.S.

It thrives in cold and damp caves and former mineral mines in the Northeast have proved to be prime territory for it.

It has long been present in Europe and Asia, and one of the leading theories is that a spelunker who explored caves abroad brought it to North America. Howe Caverns is world-renowned, and sees 200,000 visitors a year, Hicks said.

The fungus does not seem to kill bats in Europe, but Europe has far fewer bats than North America. Some theorize that it caused similar havoc there years ago without anyone noticing, and the bat population dwindled because of it.

Why the fungus has proved so problematic to only bats, and some species of bats have been hit harder than others, are additional unanswered questions.

Okoniewski said fungal infections are typically "secondary" pathogens, opportunistic invaders that cause problems to animals that are battling a virus or whose immune system is otherwise compromised.

So many biologists initially theorized that something else was afflicting the bats, such as a virus, and making them susceptible to the fungus. But Okoniewski said research seems to show that the fungus has "a unique ability to penetrate the tissues" of bats on its own.

The fact the fungus appears to be the cause of the devastation is a major issue for those trying to figure out how to reverse the trend.

Many mammals don't have much immune resistance to them.

"One of the biggest problems is resistance to fungal infections is not a common thing," Hicks said.

Fungal infections are also difficult to treat and stop from spreading, particularly among mammals like bats that huddle together to hibernate.

And while some theorized that the malady would only affect bats in cold-weather climates, Hicks said it appears caves as far south as Mexico get cold enough to allow the fungus to grow.

Bayless, from Bat Conservation International, said scientists are bracing for its southern spread.

"We don't know what's going to happen," Hicks said. "But I think this winter we'll know whether this is going to drive them all to zero."

The hope is that the fungus will not have as much impact on the remaining bats in the Northeast, since their density in caves will be far lower than usual.

More than 70 researchers and scientists working to solve the mystery met in western Pennsylvania in August, and weeks later the U.S. Fish and Wildlife Service unveiled an eight-page plan to attack the disease.

The plan spells out testing, sampling and control efforts as well as ways to raise awareness to the issue. Research is going on continually: Vermont and New York researchers plan to work together this winter to try to repopulate a cave in central Vermont whose bat population was wiped out.

But researchers know that, based on frequency of deaths, time is of the essence.

"We don't have the luxury of waiting for all of the answers before we act," Darling said.

"We're in a race to figure out what's going on," Okoniewski said.

Hicks said the bat deaths questions of whether environmental problems, such as global warming, are playing a part.

"For me, the bigger question is, what kind of world are we leaving for our children?" he asked. "Is it a world full of shopping malls were our kids can buy videos of the things that used to live here?"

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