A new mysterious and deadly illness of bats has struck New England's largest bat cave, a cavern in a Dorset mountain where 23,000 bats spend the winter, a state wildlife biologist confirmed today.

Scott Darling saw the signs as he approached Aeolus cave Thursday.

Carcasses of the tiny creatures lay in the snow. More bats flitted around the mouth of the cave, unnatural behavior for a frigid February day.

"It was as though they were running out of energy and their last effort was to go outside in search of food," Darling, a biologist with the Vermont Fish and Wildlife Department, said today.

"White-nose syndrome," which killed as many as 11,000 bats in caves around Albany, N.Y., last winter, also was identified for the first time in a Massachusetts cave last week.

In New York, the illness has been confirmed at nine caves and is suspected at two more. Aeolus is the second Vermont bat hibernaculum, or overwintering site, afflicted by white-nose syndrome.

Biologists do not yet understand what is killing the creatures - only that they have never seen this before. The dead bats are emaciated, as though starving. A white fungus furs their noses. Autopsies show lung congestion, as though they had pneumonia.

Whatever the cause, it kills with deadly efficiency. Bat populations have plummeted more than 90 percent in the two New York caves where the syndrome was first identified last winter.

The illness is so new, biologists have not yet mapped its geographic spread, nor determined what its effect might be on bat populations in the Northeast.

"It is obviously a grave concern," Darling said. "Bats are long-lived animals with low reproductive rates, so any mortality like that will take years and years to rebound from."

Among the bats killed by the illness is the tiny Indiana bat, an animal on both the federal and Vermont lists of endangered species. Darling found no dead Indiana bats in Aeolus cave, though small numbers winter there. Most of the victims were northern long-eared bats or little brown bats.

Though bats send a shiver down many human spines, they consume millions of insects as they flit through the air on summer nights and play an important role in controlling pests that afflict crops and human inhabitants.

Bats behaving strangely

Inside Aeolus cave last week, Darling and cave enthusiast Peter Youngbaer found more dead bats and about 2,000 bats flying around or hanging from walls near the entrance, also unnatural behavior.

Usually the hibernating bats stay deep in the cave where temperatures are colder and vary little.

"They were flying out of the cave, landing on the snow, landing on us - they shouldn't be doing that in mid-winter," Youngbaer said.

Darling said he expects to return as spring approaches, to try to determine how many bats died during the winter.

While pathologists try to determine what is killing the bats, three states - New York, Vermont and New Jersey - have asked people to stay out of bat caves this winter.

The Northeast Cave Conservancy has closed the nine caves it owns in New York. At least one cave owner as far away as West Virginia has also closed her cave to the public.

A call for action

Meanwhile, the Center for Biological Diversity, an environmental advocacy group, petitioned the United States U.S. government today to take additional steps to protect endangered species of bats.

In petitions to the U.S. Fish and Wildlife Service, the National Park Service, the Federal Highway Administration, the Army Corps of Engineers and the Tennessee Valley Authority, the center asks the agencies to:

• Immediately close caves and mines on federal land where five bat species hibernate in significant numbers.
• Stop activities within its control that might adversely affect the bats or their summer habitat.
• Allocate money for research on white-nose syndrome.

"Until the extent of deaths is known, all known agency actions that are likely to adversely affect the Gray bat, Indiana bat, Ozark big-eared bat and Virginia big-eared bat must cease and desist," the petition says.

Mollie Matteson, of the center's Northeast office in Richmond, said a halt to logging, road-building and other projects in prime bat habitat is necessary until white-nose syndrome is better understood.

"We don't know how it is spreading. Bats are very vulnerable because they are colonial in winter - they have very few hibernacula, so this could be a very severe blow to the population as a whole," she said.

Federal officials could not be reached for comment today because of the Presidents Day holiday.

In Vermont, Darling, the state wildlife biologist, said a discussion of new steps to protect the bats "will have to happen" soon.

"We are beginning to ask ourselves how does this affect our summer research and habitat issues," he said.