The mass deaths are difficult to quantify because wild bats are almost impossible to count, but to scientists monitoring hibernation sites, serious declines are as undeniable as they are unprecedented. Population counts at two dozen small winter colonies in Massachusetts, New York, and Vermont show they have plummeted from 48,626 bats to 2,695 -- an average 94.5 percent decline -- since the outbreak began.

The little brown bat, historically among the most common of North American bats, has been the hardest hit of the six species known to be afflicted with the baffling illness. The others are: the big brown bat, the Eastern small-footed bat, the Northern long-eared bat, the tri-colored bat (formerly known as the Eastern pipistrelle), and the Indiana bat.

“We’re at the vanguard of an environmental catastrophe,” says Tim King, a conservation geneticist with the US Geological Survey in West Virginia. “There’s very little definitive information available at this point. Everybody’s just scrambling, with very limited resources, to do whatever they can to help -- help stop this.”

At least 1 million bats in the past three years have been wiped out by a puzzling, widespread disease dubbed “white-nose syndrome” in what preeminent US scientists are calling the most precipitous decline of North American wildlife in human history. If it isn’t slowed or stopped, they believe bats will continue disappearing from the landscape in huge numbers and that entire species could become extinct within a decade. It’s enough to make some wonder: Is the bat in the cave the new canary in the coal mine?

It’s late August, when bats are in their swarming phase, and the 71-year-old Kunz and two fellow biologists have trekked, at night, in hard rain, with heavy gear, 2,520 feet up the rugged Taconic Mountains to Aeolus -- the largest bat hibernaculum in the Northeast -- to bleed live bats and collect samples for researchers leading the hunt for clues into the cause of mysterious bat deaths like these.

“What we saw was bat soup. There were a lot of bones of wings and skulls and emulsified bodies,” Kunz says. “There were dead bats -- decomposing bats -- hanging from the walls of the cave.

The renowned bat biologist from Boston University, who bears a passing resemblance to Harrison Ford, minutes earlier had recovered the bands while trudging, like a real-life Indiana Jones, through a slippery mud-like ooze of rotting bat carcasses, liquefied internal organs, toothpick-sized bones, piles of guano, and a strange white fungus on the cave floor.

Thomas Kunz emerges from Aeolus cave in East Dorset, Vermont, with a half-dozen metal ID bands -- smaller than SpaghettiOs -- cupped in the palm of his latex-gloved hand. They’re tiny emblems of death, having once been affixed to the forearms of little brown bats.

Initial white-nose studies have produced two consistent findings: The fungus has been found on bats at every site where mass deaths have occurred, and most of the dead bats are emaciated. But the link between them has evaded scientists. The leading hypothesis -- Kunz shorthands it as “itch and scratch” -- is that the fungus irritates the bats’ skin, arousing them more frequently than normal in hibernation to groom it off. Those actions, the thinking goes, squander their fat reserves until, ultimately, they starve to death.

The hallmark of the syndrome is a skin infection that creates holes in and scarring of the bats’ wing membranes, causing them to lose elasticity. “It’s challenging to think of why an animal might die of a skin infection. Isn’t that just like getting athlete’s foot?” says David Blehert, director of diagnostic microbiology at the National Wildlife Health Center in Wisconsin and lead author of the report that identified the fungus. But you can’t really liken it to that, he explains, because this infection “actively invades living skin cells.”

Researchers strongly suspect but have not proved that the sickness is caused by a newly identified cold-thriving soil fungus aptly named Geomyces destructans. (Some believe the fungus is a secondary infection that grows on bats with already weakened immune systems.) Nor have they unraveled the enigma of a perplexing chain of events that leads from an apparent fungal infection to erratic bat behavior to death by what appears to be starvation.

White-nose syndrome gets its name from the white fungus that looks like confectioners’ sugar found around the noses -- as well as on the ears, wings, and other exposed skin -- of many infected bats, though not all show signs of the disease.

In addition to Massachusetts, New York, and Vermont, the plague-like condition has been confirmed in Connecticut, New Hampshire, New Jersey, Pennsylvania, and, earlier this year, Virginia and West Virginia. It appears headed toward caves and mines in Kentucky and Tennessee, and possibly North Carolina and Ohio. (There have been no confirmed cases in Ontario or Quebec.) For Kunz and his colleagues, this winter will be telling.

Since white-nose was detected in February 2006 by a caver photographing a private section of Howe Caverns near Albany, New York -- considered the disease epicenter -- its spread, from New England to South Atlantic states, has been terrifyingly swift. Infected hibernation sites were discovered the second winter less than 20 miles from Howe; the next, about 120 miles; and by last winter, more than 650 miles.

Scientists are alarmed that white-nose syndrome, unlike many wildlife diseases, is a multi-species killer, infecting nearly every cave-dwelling bat species in states where it has struck. It attacks the bats as they hibernate in caves and mines, typically from mid-October to mid-April.

“If it continues at this pace,” says New York bat specialist Alan Hicks, “in a few years we won’t have any [of these] bats.”

The animals, which are nocturnal, are exhibiting other aberrant behaviors, such as clustering near cave entrances where it’s coldest, perhaps an attempt to lower body temperatures further to conserve energy, and flying around outside in winter, in daylight, possibly in a desperate search for food.

Because Geomyces destructans grows in chilly cave-like temperatures, optimally 41 to 57 degrees Fahrenheit, bat biologists originally thought the die-offs might end when surviving bats fled the hibernacula. But they kept on dying into May and June. “Even those bats that might make it through the winter may have sufficient wing damage that they’ve lost maneuverability and they can’t catch food very effectively,” says DeeAnn Reeder, a bat researcher at Bucknell University. “So, there’s all of these things that are happening to them, and we haven’t connected those dots.”

Heightening concerns further, female bats give birth just once a year to a single pup or twins. “They are not going to be able to rebound from this very quickly, if at all,” says Vermont Fish and Wildlife biologist Scott Darling.

Scientists are not certain how white-nose syndrome is spread but say its rapid dispersal suggests bats -- which can migrate 200 miles between summer roosts, where they intermingle, and hibernation sites -- are most likely transmitting the disease to one another. Increasingly, however, there are suspicions that humans who explore caves and mines may play a role in the spread by unwittingly carrying fungal spores, which attach to their clothing and equipment, from infected sites to clean ones. As a precaution, the US Forest Service last spring closed approximately 2,000 caves and mines in 33 states in its Eastern and Southern regions for up to one year. The action followed a US Fish and Wildlife Service request that the public observe a caving moratorium in 17 states. Since then, cave owners and managers have closed dozens more.

Of the six species of bats affected so far, only one -- the Indiana bat -- is on the federal endangered list. If white-nose syndrome continues its anticipated blitzkrieg deeper South and into the Midwest, three more species on that list are likely to be imperiled: the gray bat, the Virginia big-eared bat, and the Ozark big-eared bat. Yet even fears that some species could vanish entirely are being overshadowed by the enormity of ordinary bats, like little browns, dying by the tens of thousands. No one can predict the ecological fallout from

1 million dead bats -- some say the actual figure might be double that -- but whenever something is taken out of the ecosystem in large numbers, there are obvious concerns.