Baffled biologists scramble to unlock secrets of disease killing millions of hibernating bats

February 11, 2012

If you're trying to evoke sympathy for the plight of threatened animals, it's relatively easy to drum up support for charismatic creatures like pandas, polar bears or baby seals.

Hence the frustration of biologists trying to raise awareness about the biggest disappearance of mammals in North America today — the death of millions of hibernating bats due to a mysterious disease called white-nose syndrome.

“People are freaked out by bats. They fly around at night and we only get a glimpse of them,” said Craig Willis, a University of Winnipeg wildlife biologist who's trying to prevent what was unthinkable several years ago — the extinction of every hibernating bat species in North America.

Five years ago this month, puzzled scientists inspected a Schoharie County, N.Y., cave where bats that should have been deep in their midwinter torpor, or hibernation, were up and moving about. Many were lying dead at the bottom of the cave and some of the afflicted bats had a mysterious white growth on their faces, wings and other patches of exposed skin.

Initially perturbed, bat biologists were seriously disturbed the following winter, when the same bizarre situation — dead and dying bats by the thousands, accompanied by the same mysterious white growth — showed up in dozens of other bat hibernation locations in New York and eight other northeastern states.

By the end of last winter, what's now known as white-nose syndrome had been confirmed in 17 U.S. states and four Canadian provinces, including Ontario. A cave near Wawa, Ont., on the northeastern shore of Lake Superior, was found infected last winter, bringing the disease within flying distance of Manitoba.

Biologists like Willis are now scrambling to discover how the syndrome works and how it spreads before it reaches this province and other areas of North America. What's at stake is not just the survival of millions of bats, but an agricultural sector that relies on bats to gobble up pest species such as beetles and moths.

The little brown bat, for example, may only weigh nine grams, but a single critter is capable of consuming a kilogram of insects in a single summer, Willis said.

“Sadly, they don't eat many mosquitoes. I realize that's bad marketing, but most people don't think of the role bats play in the ecosystem, if they think about bats at all,” he said.

Willis, a 38-year-old associate professor originally from Ontario, arrived in Winnipeg five years ago, precisely as researchers in the United States first identified white-nose syndrome. Eventually, they cited the fungus Geomyces destructans as the probable cause of the disease, which appears to kill bats by waking them up at a time when there is no food for them to eat, leading them to starve or freeze to death.

What scientists do not know is exactly how the bats are being harmed by this fungus, which is also present in Europe but doesn't seem to be killing off bats overseas. It might be waking bats up by drying them out, much the same way humans wake up in the middle of the night when they get thirsty. Or it might be speeding up the metabolisms of animals that rely on two grams of stored-up fat to make it through an entire winter.

Whatever the precise mechanism, bats are dying off en masse due to something that's disrupting the way they slumber in caves, abandoned mines and other sleeping spots.

“It's pretty obvious when you find hungry bats in February and March that there's something very wrong with how they use torpor,” said Willis, who's actively conducting experiments to rule out some of the factors contributing to bat mortality.

One factor appears to be humidity, as infected caves with higher humidity seem to have lower mortality rates than dryer caves, he said. Another is the lethal fungus itself, which may be a mutated form of something that's been in North America for many years — or an invasive species from Europe.

Last winter, Willis was among a group of researchers who deliberately infected bats with both North American and European strains of the fungus in an effort to settle the mutation question. The results of this research may be published later this year, he said.

Another obvious factor is temperature, as bat species that migrate south for the winter instead of hibernating are not dying off. This raises the idea of actually heating the places where bats hibernate to slow or even stop the spread of the fungus once it arrives in Manitoba.

Other theoretical ways to prevent Manitoba's hibernating bats from dying off include the expensive and technically troublesome possibility of inoculating wild animals that are difficult to monitor, never mind catch. In theory, some sort of probiotic applied to the bodies of bats could outcompete the deadly fungus. Or bats who survive white-nose syndrome could be used to repopulate decimated caves — if, in fact, it's possible to survive the disease.

Despite the fact 200 academics across the continent are researching white-nose syndrome, Manitoba Conservation and Water Stewardship is resigned to the syndrome killing masses of little brown bats, northern long-eared bats and big brown bats by 2015.

“We're preparing for what we think is inevitable but hope will not happen,” said Bill Watkins, a conservation zoologist for the province's wildlife and ecosystem branch. “We know we have hibernating bats using the far side of Lake of the Woods, so it's only a couple of jumps away at Lake Superior.”

Most of Manitoba's known hibernating bats bed down for the winter in caves in the porous karst landscape of the Manitoba Lowlands, which runs from the Interlake up to areas north of Lake Winnipeg. Willis and his colleagues have implanted microchips in 2,000 of these animals to monitor their movements.

In the meantime, Manitoba Conservation has declared all 11 known Manitoba bat hibernation locations off limits to cavers and other visitors in an effort to prevent people from spreading fungi spores from cave to cave.

Some of the caves are on private land, which provides another level of protection. But the locations of caves on public land are being kept secret, even within provincial offices, Watkins said.

“Someone could tell a friend who could tell a friend,” he explained. “We discourage people from entering any cave that could have bats in it, particularly in the fall.”

Researchers who enter caves must wear disposable suits and disinfect their rubber boots before entering. The Speleogical Society of Manitoba, which promotes caving, has warned its members to stay away from bat caves.

All of Manitoba's bat species — the three hibernating species, plus three others that migrate south — have long been protected under provincial legislation. The province is also working on a management strategy to deal with bats once white-nose syndrome arrives.

Somewhat ironically, before the appearance of white-nose syndrome, North America's bats were doing relatively well, having recovered from decades of persecution in the early 20th century. Although some people continue to fear bats and associate them with witches and vampires, Willis said, younger people are more likely to see them as cute critters.

Ordinary people can help keep up bat populations by installing bat houses on their properties, said Willis, qualifying that comment by warning bats are unusually rare inside the Perimeter Highway.

The reasons for this are unknown, though he suspects decades of malathion use could be a factor.

“I don't even want to get into that,” he said. “We have enough to worry about as it is.”

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