Dark night for bats

Stone hypothesizes that dry summers over the past few years may have caused a decrease in the bats' insect prey, and that warm spells in recent winters may have triggered bats to awaken and burn up energy, which they couldn't replenish. "It would appear they were burning a lot more energy than they were taking in," he says. Climate change may have also allowed for the spread of the white-nose fungus, which may have been hiding under our noses for years, he says.

Despite his strong convictions, Stone can't explain how a warming climate would favor the spread of a cold-loving fungus, and he doesn't yet have evidence to directly link climate change to any of the symptoms of WNS. Stone has some respectable achievements under his belt; he was the first person to identify West Nile virus in the United States. But he's something of a contrarian, and hasn't convinced many other scientists of his theory. At a recent meeting of bat biologists, Darling says, the majority of attendees agreed that global warming was not a leading hypothesis.

That doesn't mean humans are off the hook. Many researchers say it's likely there is no WNS silver bullet, and that the syndrome may be caused by a thorny combination of factors. "Are they exposed to a new fungus? Is there a toxin depressing their immune system? Is there a problem in their food supply?" Buckles wonders. "Most diseases are multifactorial. We're not in a situation where we can rule anything out."

Buckles has looked for high levels of contaminants like lead and PCBs, and for chemicals from pesticides or other environmental toxins. The Northeast is downwind from the rest of the country's pollution, and all manner of agricultural pesticides are introduced into the landscape each year. Again, though, no obvious suspects have emerged. However, a pair of researchers in the Midwest recently uncovered intriguing data that hints pesticides may be involved.

John Whitaker is a biologist at the Center for North American Bat Research and Conservation at Indiana State University. Several years ago, he and collaborator Kathleen Dannelly, a microbiologist at ISU, discovered an enzyme called chitinase in the guts of bats. This enzyme breaks down chitin, the major component of insect exoskeletons. But mammals weren't known to produce chitinase. Digging deeper, the pair discovered a garden of chitinase-producing bacteria in the bats' intestines. The scientists concluded that the beneficial bacteria were helping bats draw energy from otherwise indigestible insect parts.

Whitaker dissected some hibernating bats. He found no fresh food in their stomachs -- not surprising in the middle of winter. But he did find pieces of chitin, presumably left over from the bats' summer meals. Whitaker and Dannelly believe the chitin pieces stored in the bats' guts are slowly digested over the winter, giving the bats extra energy to get through the season. So when they heard about a new syndrome causing bats to waste away while they hibernated, they were eager to take a look.

Whitaker and Dannelly examined 12 little brown bats from New York, all found dead in caves where WNS was rampant. Inside the bats, they found plenty of chitin. "We could see bug legs and wings," says Dannelly. But the chitinase-producing bacteria were harder to come by. She took multiple samples from each of the bats, up and down the intestinal tracts. She found extremely low numbers of the beneficial bacteria in one bat. In the remaining 11, she found none at all.

Dannelly's hunch is that a toxin may be killing off the symbiotic bacteria in the bats' intestines. "Maybe they're using a new pesticide [in the Northeast] and it's becoming more widespread," she suggests. Theoretically, bats could take in traces of a pesticide with their food or drinking water. If the chemical wiped out the beneficial bacteria, the bats couldn't break down the chitin in insect parts. It's the energy from that chitin, Whitaker believes, that may give bats the boost they need to survive the winter.

According to Dannelly, at least one relatively new pesticide is known to be toxic to chitinase-producing bacteria. "So far nobody has been able to tell me if it's used in the New York area," she says. She declines to give pesticide names, since she doesn't have evidence implicating any specific chemical. And she and Whitaker admit their data isn't perfect. They examined only 12 sick bats, and they weren't able to examine healthy bats from the Northeast to use as a control. Instead, they compared the gut bacteria of sick bats with those of healthy little brown bats from Indiana. Their findings are "a powerful clue" that the disease may be linked to a loss of beneficial bacteria, Whitaker says. But it's not an answer. "We haven't proved it yet."

He and Dannelly are hoping to get their hands on more bats to boost their sample size. Meanwhile, they're attempting to calculate exactly how big a role chitin plays in the bats' total energy needs, in both summer and winter. Whitaker adds, with slightly detectable disappointment, that his idea hasn't gotten much attention from his colleagues. The theory "hasn't risen to the top of the pile," admits Hicks, who has emerged as the de facto leader of the WNS investigation. Then again, he says, "nothing much has. We're fishing now. Anything that shows potential, we'll pursue."

While lab scientists such as Buckles and Stone continue to pursue the fungal clues, field biologists like Darling are keeping tabs on the health of the bats, hoping to have a better sense of the animals' condition when they enter hibernation this fall. By Darling's count, more than 25 agencies and institutions are contributing to the effort.

They may not all see eye to eye on which angles to pursue, but nearly everyone agrees the syndrome could be disastrous to the bat population. Bats can live up to 30 years, and females give birth to just one pup per year. At that rate, it could take a very long time for a broken bat population to recover. The animals migrate hundreds of miles between hibernacula and summer foraging grounds, mingling with bats of other species and from many states. In its first year, WNS spread between 80 and 130 miles from the apparent epicenter in Albany, N.Y. "I'm afraid it could spread right across the country," says Hicks.

Darling worries that caves that appeared healthy last winter may have been in the early stages of the syndrome. "It may progress in such a way that it takes a couple of years for sites to be maximally affected," he says. If that's true, "we might be facing a really traumatic winter for the bats."

On the evening I spend bat-trapping with Darling, his primary mission is to catch a female Indiana bat and fit her with a radio transmitter. If all goes as planned, the transmitting bat will lead him and his team to the maternity roost, a tree where a mass of mother bats and their pups sleep off the daylight hours. If he can find the tree, he can better estimate the size of the endangered bats' reproductive population.

On this night, the team is energized by success. Two female Indiana bats land in the net within the first two hours. Both are lactating (a fact that wildlife technician Brissee establishes by squeezing the tiny bats' even tinier teats to look for milk), and will likely be heading to the maternity roost as day breaks. The biologists carefully glue the minuscule transmitters to the animals' backs and, one at a time, set them free.

It's just after midnight and the cloudless Vermont sky is overflowing with stars. We watch the last bat fly off, beeps from the transmitter antenna growing fainter as the female flutters away into the darkness. It's a magical moment, and I want to be optimistic for this bat and its kin. But white-nose syndrome hasn't offered much reason for optimism. "It could be years before we have an answer," Darling had told me earlier, as he trudged through the tall meadow grass with a squeaking bat in his hand. "I'm not sure the bats have that long to wait."