As dusk settles on summer evenings in the Northeast, the buzzing of insects fills the air. Soon after, bats emerge from their roosts, swooping gracefully to snatch flying bugs. But this timeless interplay may be thrown out of whack because of a puzzling ailment that killed shocking numbers of insect-eating bats in New York, Massachusetts, Connecticut, and Vermont this winter. Dubbed “white-nose syndrome” for the circle of white fungus on sick bats’ noses, the mysterious illness has wiped out tens of thousands of the mammals, and wildlife managers are racing to identify it.

The sick bats lose their winter fat reserves too fast and starve. The fungus is an obvious suspect,  but scientists believe it’s a symptom, not the cause. Whatever the source, white-nose syndrome is spreading: First noticed in four caves in New York in January 2007, it may have killed as many as 11,000 bats last winter. This year, the malady spread to more than 20 caves and mines, expanding from a 7-mile radius to an 80-mile radius. More than 500,000 bats hibernate in the affected sites, and some biologists fear half could disappear. “This is unprecedented in the annals of bat biology,” says Thomas Kunz, a Boston University biologist. “I’ve been working on bats for 40 years, and I’ve never seen anything like this. We’re grasping at straws.”

Bat welfare is a concern partly because of their voracious appetites. A small colony of 500 bats that weigh one-third of an ounce each will consume 5 to 10 pounds of bugs a night. Scientists fear large die-offs could cause insect populations to explode, which could lead to  gardeners and farmers in the Northeast taking a hard hit from pests in the spring. “If you remove top predators like bats, it could throw the ecosystem out of balance,” Kunz says.

Hoping to stave off disaster, virologists, bacteriologists, toxicologists, and dozens more experts from universities, environmental consulting firms, and government agencies are racing to figure out if an infectious agent, a toxin, or some other factor is killing bats. In addition, caving groups have asked members to stay above ground until May 15 and to report previous expeditions to state wildlife agencies in case humans are spreading the syndrome. Kunz’s lab is looking at whether the sick bats’ immune systems are compromised and trying to understand the cause of the fat reserve loss—in January, bats’ energy stores, which usually last through April, were nearly depleted.

Bats hibernate deep inside mines and caves and stir if they’re disturbed. “If you’re in a cave with 50,000 bats for two hours, by the time you leave, they’re moving around so much it sounds like rustling wind,” says Al Hicks, a bat specialist with New York’s Department of Environmental Conservation. But in affected caves, bats cluster near the entrance—perhaps because it’s colder there and they can conserve more energy—and don’t rouse when people enter. Equally unusual is the sight of sick bats flying outside mid-winter. “If bats are running through their reserves, the last thing they do is either die in the roost or fly outside hoping there’s a meal,” says Hicks. “It’s their last gasp.”

Investigations this summer might shed light on the problem. Bats can travel hundreds of miles between winter roosts and summer homes, called maternity roosts, and not all residents of one summer colony winter together. This behavior may be spreading an infectious agent, or there may be something deadly at a maternity roost. To find out, researchers may visit summer colonies to count bats as they exit at dusk to feed and study environmental conditions there. “We’ll go back to these areas and see if there are any bats left,” says Robyn Niver, a US Fish and Wildlife Service biologist.

Little brown bats are suffering the biggest losses, but Indiana, eastern pipistrelle, northern long-eared, and small-footed bats are also dying. Wildlife managers are especially worried about Indiana bats because they’re endangered. “I’ve spent my entire career looking at Indiana bats, and we were just thinking we might be able to get them off the [endangered species] list,” says Hicks. But he’s optimistic about the widespread efforts to find the answer. “This level of support is what it will take to find out what’s killing bats.”

Story by Alisa Opar. This article originally appeared in "Plenty" in June 2008.

Copyright Environ Press 2008

Bat grave
Scientists are racing to discover what killed thousands of bats in Connecticut and other states.