An ailment that has stumped scientists and has killed thousands of bats in New York and Vermont is now afflicting bats in Berkshire County and other parts of Massachusetts.

The mysterious sickness has been dubbed "white-nose syndrome" due to one of the symptoms that can be spotted with the eye - white, powdery fungus coating a bat's nose.

Tom French, assistant director of the endangered species program at the Massachusetts Division of Fisheries and Wildlife, visited Berkshire County caves in Cheshire, Sheffield and Egremont and two in Chester (Hampden County) within the last three weeks.

Outside each of the caves, dead bats were found on the ground. Some bats were observed flying in and out of the caves, something that French said is peculiar for this time of year.

"They shouldn't be out of their caves during the daytime, and especially during the cold winter months," he said.

Preliminary tests show that the bats' fat reserves are being depleted during hibernation, which typically lasts until late April, and they're leaving their caves early to search for food and water.

"They're coming out in a desperate effort to eat," he said. "And they're starving to death."

French said the condition has stumped biologists and has international bat experts worried. It's unknown whether the deaths are being caused by a bacteria, disease or toxin.

The U.S. Fish and Wildlife Service's disease laboratory in Wisconsin is testing dead bats pulled from Massachusetts caves. Labs in California and Florida are also testing for clues. Wildlife officials from Massachusetts, Vermont, Connecticut and Pennsylvania have been holding weekly conference calls to keep everyone updated

"This is unprecedented," French said. "International scientists have never seen anything like this before."

The condition was first discovered in January 2007 in a cave near Albany, N.Y. Later that year, it was found to have spread to a number of other upstate New York caves, killing an estimated 11,000 bats.

By February of this year, the syndrome had spread to caves within a 100-mile radius of Albany. Bats with the white-nose syndrome were found recently in caves in southwestern Vermont, including Williams Cave in Pownal.

Vermont Fish and Wildlife biologist Scott Darling said "There may be something about the caves in (this) region," that is altering the bats' system, causing them to lose weight and allowing the fungus to grow on the wet membranes of their noses.

The mortality rate has reached as high as 97 percent in some caves, but it's not known how long the bats are able to live once they've contracted the syndrome.

French said Massachusetts has a winter bat population of roughly 12,000 bats, with about 1,000 of those in Berkshire County.

Chester is home to the largest bat population in the state, with roughly 8,000 of the winged creatures living in its caves. U.S. Fish and Wildlife Service biologist Susi von Oettingen recently visited the Chester caves and documented the problem on film. Her 5-minute video has been posted on YouTube.

The total number of dead bats in Massachusetts has not reached an alarming number, French said, but researchers expect the animals to start dying by the thousands next month.

French said one positive sign is that the syndrome is only affecting those species of bats that winter in caves and mines, not those who hibernate in barns, homes or abandoned buildings or who head south during the cold months. But it's not known if the infected bats will transmit the condition to bats returning this spring

Since bats are crucial to controlling the insect population, French said, this season's pesky-pest problem could be worse. The syndrome does not appear to pose any health risks to humans, however.

"Bats are voracious eaters and eat their weight in insects in one night, so it could have an impact on our insect season," French said. "We don't know what's causing it, but we know it's been catastrophic. We have a lot of questions."