The first time white-nose syndrome really hit Aeolus Cave, on the side of a mountain in Dorset, Vt., the carcasses littered the entrance like a carpet. “You couldn't step on the ground without stepping on dead bats,” says Scott Darling, a biologist with the Vermont Fish and Wildlife Department. “Nowhere else have people seen that level of mortality in a cave.”

Bats afflicted with the fungus during their hibernation usually “fly out and die on the landscape,” unnoticed. But “in Aeolus Cave, for whatever reason, many, many died right there in Guano Hall,” the steeply sloped tunnel-like cave entrance. Statewide, Vermont lost 90 percent of its bats between 2008 and 2010, the first years of the epidemic. The other 19 states and five Canadian provinces where white-nose occurs have experienced similar losses. It may be the most precipitous decline in any animal group ever, with an astonishing 5.7 million bats now thought to have died. But Aeolus, the site of decades of pioneering research on bats, became the poster child of the epidemic.

Now, Darling sees the first tentative signs of a possible recovery.

In an experiment at Aeolus in April 2012, researchers placed identifying bands on bats emerging from hibernation. When they went back to count them last April, 50 percent had survived. According to Darling, some banded bats have been known to survive as long as six years in other white-nose areas.

“We don't know if it’s something genetic or something behavioral,” says Darling. But these survivors of the great die-off seem to have a kind of resistance or resilience. “Immunity” may be too strong a word. Somehow, though, they live normal lives despite hibernating in a cave heavily infected with white-nose syndrome. “There’s hope here in the Northeast that we’ve seen the worst of it,” says Darling. But he adds that there is “a lot of uncertainty. Are we still losing 20, 30, 40 percent?”

White-nose fungus originated in Europe, where it does not appear to harm the bats. But in North America, where it first appeared in 2006, it has caused devastating losses to seven species. The disease causes hibernating bats to wake up in the middle of winter, and it is a disturbing sight. I visited Aeolus in the 1990s, long before white-nose appeared. Biologists conducting bat counts in winter were careful to whisper, to avoid waking the hibernating bats that covered the ceilings and walls.

A bat in deep hibernation drops its heart rate from as many as 1,300 beats a minute to as few as eight. Once disturbed, the bats seem to sway visibly, as they shiver toward wakefulness. They warm themselves up at a rate of about one degree a minute. Some shift their forelimbs, making the slow, dreamy, ineffectual movements of a person trying to fend off a nightmare.

Because there are no insects to feed on in winter, bats must get through hibernation with stored body fat. It makes up 30 percent of their body weight at the start and drops down to as little as 5 percent by spring. The trouble with white-nose fungus isn’t just that it wakes bats in midwinter; the effect is to send them out looking for food that’s not there. A single day of waking can burn 10 to 30 days' worth of stored fat, meaning death.

Even if a recovery occurs at Aeolus and spreads to other states, Darling warns that the bats are “not rebounding yet.” Any recovery will inevitably be slow. Despite their small, somewhat mousy appearance, bats do not breed like mice. They are remarkably long-lived. Researchers have recovered bats at Aeolus 30 years after they were originally banded. Each female also produces only a single offspring a year.

So the devastating consequences of the white-nose epidemic are likely to be evident for decades to come, in the form of mosquitoes and agricultural pests not eaten. (In one study at Aeolus, a single bat caught and ate 175 mosquitoes in a 15-minute period.) A 2011 study in Science magazine estimated that the loss of bats from white-nose syndrome and other factors is now costing North American farmers more than $3.7 billion a year.

Whether this will begin to change anytime soon depends on another experiment in progress at Aeolus. At the beginning of winter, researchers glued tiny radio tags to the backs of 450 bats there. A big, hoop-shaped receiver antenna, positioned in a passageway leading to the cave entrance, will register every time those bats go in or out.

Roughly a month from now, Darling and other researchers will make the climb back up to Aeolus. They hope to confirm last year’s promising results. If it’s good news, church bells will ring out across New England and perhaps beyond, even if the bell towers themselves remain, for now, empty of bats.