Bats are flying ambassadors of Halloween, adding spooky ambience to countless forests, graveyards and haunted houses. Lately, however, the tables have turned — Halloween and the winter it foreshadows are an increasingly scary time to be a bat in America.

 

That's because a deadly, cave-dwelling disease is sweeping across the Eastern Seaboard, killing 90 to 100 percent of bats in some colonies. Like Freddy Krueger, this killer waits until its victims are asleep, but it's even more mysterious than the sweater-clad Elm Street villain. Three years after first appearing in a single New York bat cave, the fungus has now infected 81 caves in nine states, and scientists still aren't sure where it came from, where it will go next or even how exactly it kills.

 

"We can't directly link the fungus to organ failure or anything like that," says U.S. Fish and Wildlife Service biologist Susi von Oettingen. "It certainly is ultimately responsible for the death, but we're not sure how."

 

Scientists are sure, however, that it's bad news for millions of American bats, which recover slowly from population loss since many have just one offspring a year. Bat experts are also worried the disease, known as "white-nose syndrome," will soon begin hopping through vast cave networks underneath the Midwest and Southeast, potentially wiping out endangered species like the gray bat and the Indiana bat.

 

And what's bad for bats is often bad for people, too. As a top predator of flying insects, bats regulate the population size of everything from gnats, flies and mosquitoes to costly agricultural pests, and they play key ecological and economic roles throughout the United States — making a batless Halloween even scarier than one swarming with them.

 

A long winter's nap

Bats are one of the most successful and diverse mammals on Earth, ranging from 4-inch, sub-Arctic furballs with sonar to tropical "macrobats" with 6-foot wingspans and primate-like vision. (Bats are not rodents, despite appearances, and are actually more closely related to primates than they are to squirrels or mice.)

 

Many North American bats pay a price for living in colder climates, though. Their frequent flapping uses a lot of energy, and freezing temperatures virtually eliminate the protein-rich insects they eat. Some species migrate south, but the majority of U.S. bats tough it out by hibernating in caves or mines until the bugs come back in spring.

 

Surviving a frigid New England winter with no food isn't easy, and bats undergo extreme physiological changes so they can conserve enough energy. They slow down their heart rates, suppress their immune systems and drop their body temperatures to within one degree of the ambient air. They enter this low-power, near-death state for up to two months at a time, waking up periodically to stretch, preen, relieve themselves and sometimes mate. These hibernation breaks use up about 90 percent of the energy bats have stored for the winter, so it's critical that they only wake up at the right times.

 

Despite its high stakes and risks, hibernation has worked for millennia. It wasn't until the early 20th century that it began to fail for some bats, and only then because of cavers and scientists who disturbed their hibernation without understanding the consequences. Combined with increased pesticide use, habitat loss and bats' naturally slow reproduction rate, this decimated several U.S. bat species over the decades — Indiana bats, for example, fell by 50 percent from 1967 to 2005, and now half of the species' worldwide population spends winters in just two caves.

 

But today, all 25 U.S. species of hibernating bats face perhaps the greatest threat to their biological business model they've ever seen. The seemingly safe caves and mines where they've always sought refuge are increasingly infected with Geomyces destructans, a previously unknown fungus that's now being implicated in North America's steepest wildlife decline of the past century.

 

A curiosity killed the bat

In February 2006, a caver spelunking in upstate New York found groups of hibernating bats with a strange white fuzz growing on their snouts (left). Looking around further, he also noticed several dead ones. He shot some photos, but the winter soon faded with little cause for alarm.

 

The next winter, bats at several caves in the area started behaving strangely — waking up from hibernation too early, then flying outside as if spring had arrived — and many once again featured the distinctive white fuzz on their noses, ears and wings. By January 2007, the New York Department of Environmental Conservation was aware of the outbreak, and state biologists documented a few hundred local bat deaths.

 

In the nearly three years since, hundreds of thousands more bats have died, and some estimates put the total at 1 million. White-nose syndrome has now spread north to the Canadian border, east to the Boston suburbs, and down through the Appalachian Mountains into southwestern Virginia (see map below). 

 

Fungus among us

Scientists know the disease can be transmitted between bats within a colony, but they have yet to figure out how it's moving from cave to cave. One leading theory suggests people are the carriers.

 

"Looking at how it jumped and where it jumped to in Virginia, there may also be some human transmission — that is, a human caver transmitting it to bats, then bats to other bats," von Oettingen says. "We haven't done any clinical trials of that, though, of it being in the mud on someone's boots and then spreading to bats. It's just superficial evidence."

 

Still, the decline in bat populations has been so drastic that state and federal agencies are closing dozens of caves anyway, and the Fish and Wildlife Service in March issued an advisory calling for a voluntary halt to all caving in affected states. Going spelunking in almost any bat cave from Vermont to Virginia is quickly becoming an ecological faux pas, and the fungus now looms over a sprawling labyrinth of caves in the Midwest and Southeast that serves millions of hibernating bats each winter, including four endangered species.

 

So far, cave closures are about the only thing wildlife managers know to do. The fungus that's suddenly threatening virtually all hibernating bats in North America was unknown to science before 2006. Its indirect style of killing its hosts is equally novel.

 

"This has never been documented anywhere before, worldwide," von Oettingen says. "This is a first."

 

While the species is new, however, the genus isn't. Many variations are common throughout the United States, and researchers have long noticed a similar white fungus growing on the faces, ears and wings of hibernating bats in Europe. It doesn't seem to kill European bats, but the similarities have raised plenty of suspicion that the culprit behind white-nose syndrome may be an invasive fungus from Europe. That theory is still speculative, von Oettingen points out, but she adds that "preliminary and limited genetic analysis does suggest there may be a genetic connection."

 

"They certainly look very similar, under a microscope and physically when you're actually looking at the bats," she adds. "Right now the Europeans are doing intensive genetic analyses, to see if they're the same, or if one is a mutation of the other. Hopefully they will publish something very soon."

 

From cave to grave

White-nose syndrome doesn't directly damage, or even infect, any of bats' internal organs. Geomyces destructans comes from a family of cold-loving, "keratinophilic" fungi, meaning they feed on keratin, the substance that makes up skin and hair.

 

But if bats' vital organs are left untouched, what's killing them? And what possesses them to fly outside?

 

"One of the theories is, because it's invading the skin in winter, it could be an irritant, waking up the bat from hibernation because it itches and causes stress," von Oettingen says. "The bat may then leave the cave simply to try to flee the itching."

 

Although the case against Geomyces destructans is still in its infancy, most affected bats seem to die from starvation, having exhausted themselves by flying around — or even just being awake — when no food is available. Their dead bodies often have little or no fat left on them.

 

Other theories range from wing infections, which might disrupt bats' temperature-regulating abilities, to disorientation and confusion, which could be what sends them flapping crazily into the outside world. Some insect-eating members of the Cordyceps fungus family even control their host's body, send it zombie-walking to an open location and then kill it, all so a mushroom can grow from its corpse and release new spores into the wind.

 

While Geomyces mushrooms aren't likely to start sprouting from dead bats, Cordyceps is an extreme example of how aggressively adaptable such predatory fungi can be. In an online article about white-nose syndrome, U.S. Geological Survey biologist Paul Cryan says Geomyces destructans — a fungus that lived in obscurity four years ago — "appears to be exquisitely adapted to persist in caves and mines and to colonize the skin of hibernating bats."

 

Lights at the end of the tunnel

Sometimes natural immunity emerges as a ray of hope during disease outbreaks, but von Oettingen says there's no sign of it yet with white-nose syndrome.

 

"We haven't found any, and we haven't even been able to locate a banded [radio-monitored] bat that's survived," she says. "We've just been finding dead ones."

 

Finding a cure, vaccine or treatment won't be easy, either. It would need to be something that can easily be applied to a large number of bats, is safe for bats, is safe for people, and isn't deadly to other, beneficial fungi that also live in the cave.

 

Scientists are still fighting, though, armed with grant money the Fish and Wildlife Service has set aside for white-nose syndrome research. In March, a pair of researchers proposed putting space heaters in bat caves to help sick animals save enough energy to survive the winter. Another team recently set up video cameras in a New York mine where white-nose syndrome has been hitting bats hard, as well as a cave where it's expected to spread this winter. They'll be looking for unusual behavior in the bats — excessive grooming, long bouts of activity or wintertime flying — to find out for sure whether they're symptoms of a Geomyces destructans infection. And this week, wildlife biologists in Vermont began repopulating two affected caves with 79 healthy bats to see if such reintroduction efforts can work.

 

The urgency of white-nose syndrome is driving a flurry of similar research this year, and von Oettingen says it could be a pivotal winter for discovering the disease's secrets, and for planning how to save endangered bat species before it's too late.

 

"This year's going to tell it," she says. "If it spreads even more rapidly than last year, that gives us an indication of how fast this is going to go and how devastating it can be. But if we're able to find at least some short-term treatment, maybe we'll be able to slow the spread, or at least contain it.

 

"I am hopeful this year that we are able to find a treatment," she adds, "or maybe find out the caves in the Southeast just have a different environment, and it stays confined to the Northeast. But most biologists you talk to think it will keep spreading."

 

 

More information

For more about white-nose syndrome and other bat issues, check out the video above and the following links from MNN:

And for the latest news, information and caving advisories regarding the spread of white-nose syndrome, try these government websites:

 

Photos: Furryscaly/Flickr, Kentucky Department of Parks, U.S. Fish and Wildlife Service, National Park Service

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