WHITE-NOSE SYNDROME: Little brown bats photographed in a New York hibernation cave. Most of the bats exhibit fungal growth on their muzzles.
Courtesy of Nancy Heaslip, N.Y. Department of Environmental Conservation

People near Albany, N.Y., began noticing the strange bat behavior at least two years ago: Droves of the normally nocturnal mammals were seen flying around on brisk winter days when they should have been hibernating in caves for the season. The state's Department of Environmental Conservation (DEC) teamed up with the U.S. Geological Survey (USGS) to investigate and made an alarming discovery: Bat populations throughout northeastern New York State, Connecticut, Maine and Vermont had thinned by as much as 97 percent in area bat caves and emaciated survivors were found hanging near cave entrances where it is typically too cold for them to stay the entire winter. The only clue to the mysterious phenom was a white, powdery organism on the muzzles, ears and wings of the dead and dying bats.

Scientists have since linked the deaths of more than 100,000 of the smaller species of brown bats, northern bats, tricolored bats, Indiana bats and small-footed Myotis, along with larger brown bats in the U.S. Northeast to a condition they dubbed "white-nose syndrome." These researchers suspect that, since the winter of 2006, the ailment may have contributed to a steep decline in the bat populations at many caves in the affected states; in the most extreme case, about 1,750 of 1,800 of the flying mammals were found dead. Bat declines at many surveyed hibernation caves exceeded 75 percent.

"If you apply this across [the northeastern U.S.] there could be 200,000 dead bats and possibly even more," says David Blehert, a USGS microbiologist and lead author of a paper on the syndrome published today in Science.

USGS scientists are working with New York State environmental and health officials to pinpoint the exact cause and consequences of the fatalities. A breakthrough came in April when Blehert identified the white organism on the critters' noses as a type of geomyces fungus, one of a group of organisms that live in soil, water and air and reproduce at refrigerator temperatures of 39 degrees Fahrenheit (four degrees Celsius), the temp in most bat caves.

"When bats are torpid [in a hibernating state], they drop their temperatures down to the ambient temperatures of the caves," Blehert says. This makes the dormant bats susceptible to infection by this fungus.

But researchers are in the dark about the source of geomyces. They don't know if its spores were carried to the bat caves by animals or the wind or if it was in these caves all along and recently spread to spots where the bats hibernate.