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24 Mar 2011

In Aeolus Cave, A Search for the Vanishing Bats of the Northeast

When wildlife biologists ventured into a Vermont cave this month, they found disturbing evidence that white-nose syndrome was continuing to take its toll on once-abundant bat populations. But the question remains: What can be done to halt the spread of this still-mysterious ailment?
By elizabeth kolbert

Aeolus Cave runs into the side of a mountain in Dorset, Vermont, like a tunnel. At its mouth, there’s a large chamber with a vaulted ceiling, which has been nicknamed Guano Hall. Further along, the cave narrows into a network of passageways so tight that no one knows how far they extend. In the 1960s, a team of biologists estimated that a quarter of a million bats gathered each winter in the passageways of Aeolus to hibernate. Many doubted this estimate, but later studies confirmed it.

View photos
White Nose Syndrome Bats

Photo courtesy of The Nature Conservancy
Researchers inside Aeolus Cave in March, 2010.
One day earlier this month, Scott Darling, of the Vermont Fish and Wildlife Department, Susi von Oettingen of the U.S. Fish and Wildlife Service, and David McDevitt of the Nature Conservancy, snowshoed up to Aeolus Cave to count up how many bats remain there. It was a bright blue day and a recent storm had coated the trees with a thick layer of ice. Near the entrance to the cave, the group stopped to have lunch; it was observed that after the count, no one would really feel like eating. Darling handed out helmets and Tyvek suits, which he’d been carrying in his backpack.

As is the case with most hibernacula in New England, the bat population at Aeolus has been hard-hit by white-nose syndrome, the still somewhat mysterious ailment first detected in upstate New York in the winter of 2007. In the winter of 2008, Darling arrived at Aeolus and found the cave littered with dead bats. The following winter, there were so many dead bats on the floor of the cave that they formed a sort of a carpet. By last winter, the dead bats had decomposed, and the ground was covered in tiny bat bones.

In a normal year, there used to be between 1,000 and 3,000 bats hanging from the ceiling in Guano Hall. Last winter, the count in the hall was down to 112. Assuming that the hall is representative of the cave as a whole, this means the bat population at Aeolus had plummeted by at least 88 percent.

Here’s what is now known about white-nose syndrome: the powdery white substance that gives the syndrome its name is fungus from the genus Geomyces. (For its destructive power, it’s been named Geomyces destructans.) Geomyces destructans grows only in cold conditions — when
Some evidence suggests the fungus was brought to the U.S. from Europe, perhaps from an unwary spelunker.
bats hibernate, their body temperature drops to the level of their surroundings — and it sends out hyphae, or filaments, that enter the bats’ skin through their glands and hair follicles. It’s able to break down bat tissue – a recent paper described it as “digesting, eroding and invading the skin of hibernating bats” — which, as Darling observed, “is a very unusual behavior, if you can use that term, for a fungus.” White-nose syndrome can be spread from bat to bat, and experiments performed in Vermont have shown that bats can also contract it from the environment.

Still, it’s not clear exactly how white-nose kills bats, or if in fact it does. One hypothesis is that the fungus kills them directly. Another is that it irritates the bats, which causes them to wake from their torpor and use up the fat reserves they need to survive the winter. A third is that white-nose is an opportunistic infection that reflects some deeper, immunological problem. It’s not clear how Geomyces destructans was introduced into caves in the Northeast, though some evidence suggests that it was brought in from Europe, perhaps by an unwary spelunker.

Once everyone had suited up, the group made its way to the mouth of the cave. Even before white-nose hit, the Nature Conservancy, which owns Aeolus Cave, had installed a gate across the entrance to protect the bats from disturbance. McDevitt fished out a key and, after several tries, managed to remove one of the slats from the gate; this created an opening just big enough for a person to crawl through.

Inside Guano Hall, icicles hung down from the ceiling, and knobs of ice rose up from the ground, like columns. The floor was still covered in tiny bat bones, but the ceiling, which just a few winters ago was covered with
The floor of the cave was still covered in tiny bat bones, but the ceiling was nearly empty.
clusters of hibernating bats, was nearly empty. Darling gestured toward a hollow in the cave wall. “That area used to be covered in bats,” he said. “This is damn near dead.” The group searched for an hour, and managed to locate just 35 live bats — 33 little brown bats (Myotis lucifugus) and 2 northern long-eareds (Myotis septentrionalis). One of the bats was awake and grooming itself, probably a sign, von Oettingen observed, that it was suffering from white-nose.

“I guess the question is: What’s going to be the bottom here?” she said. “We do have sites with none.”

Darling said that in hibernacula that have been monitored in Vermont, populations are down between 85 and 100 percent compared with just five years ago. Other states — white-nose has now been detected in 13 states, from New Hampshire to Tennessee — have reported similar mortality rates. It’s been estimated that since the syndrome was first observed, at least a million bats have died, which, as one recent publication put it, “far exceeds the rate and magnitude of any previously known natural or anthropogenic mortality events in bats, and possibly in any mammalian group.”

View photos
White Nose Syndrome Bats

USFWS/Wikimedia
The powdery white substance that gives white-nose syndrome its name is fungus from the genus Geomyces.
On the way back down the mountain, Darling discussed efforts to find a cure for white-nose. In the lab, Geomyces destructans can be killed by a variety of anti-fungal agents, including athlete’s foot medications. But when wildlife biologists in New York tried to treat hibernating bats with an anti-fungal agent, all of the treated bats died — though whether from white-nose or from being handled is not clear.

Vermont is now in the process of adding little brown bats and northern long-eared bats to the state’s list of endangered species. The proposed listing of the little brown is particularly shocking, as the bat was, at least until recently, the most common in New England — so much so that no one paid much attention to it.

“Five years ago, if you had asked me, ‘Well, can you imagine anything that would make your little brown bat go to one of your rarest species,’ I probably would have laughed and said, ‘No that’s not even possible,’” Darling said. “Even if it’s an invasive fungus, to think that it could have a regional impact that fast would be really surprising.”

“The difficult thing is, well what do you do about it?” he continued. “And I wish I had answers for that.”

ABOUT THE AUTHOR


Elizabeth Kolbert has been a staff writer for the New Yorker since 1999. Her 2005 New Yorker series on global warming, “The Climate of Man,” won a National Magazine Award and was extended into a book, Field Notes from a Catastrophe, which was published in 2006. She is a regular contributor to Yale Environment 360. In previous articles for e360, she has reported on a study that found the pace of global warming is outstripping projections and about the scientific debate over whether to designate a new geological epoch to reflect the changes caused by human activity.
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COMMENTS


A well written and dramatic article! This is truly a major environmental disaster!

We too are working to save bats at my Lab and continue to be thoroughly astonished at the rapid demise of individuals within a cave or region.

Posted by Dr. Andrew N. Barrass on 25 Mar 2011


Thank you for the article. However, I find it in very poor form to place in the insert that "spelunkers perhaps were the cause ..." when the St. Lawrence Seaway is just a few miles north of ground zero. and there are several documented occurances of bats crossing the Atlantic on ships. Include that in your next article. U.S. Fish and Wildlife have a theory, blame people. Ask them to provide you the study showing this.

Thanks again for the article.

Posted by Ray Keeler on 25 Mar 2011


Here a video piece I did on Aeolus Cave several years ago when white-nose first hit. If you want to see what the cave floor looked like when bats were dying inn hug numbers have a look:

http://www.youtube.com/watch?v=a0JoPbSBnqo&feature=player_embedded

Posted by Gerrit on 27 Mar 2011


I also dislike your comment, as did Ray Keeler, that "It’s not clear how Geomyces destructans was introduced into caves in the Northeast, though some evidence suggests that it was brought in from Europe, perhaps by an unwary spelunker."

The first recorded occurrence of white nose syndrome, in 2006, was in the downstream section beyond the commercial show cave Howe Caverns, in Schoharie County, New York. Well over 100,000 persons visit Howe Caverns annually, as opposed to a much smaller number of "spelunkers" visiting northeastern caves. It is much more likely to have been introduced by a visitor to Howe Caverns who had been in Europe.

Posted by Chuck Porter on 29 Mar 2011


Would it be possible, or even feasible, to treat infected bats with a vaporisor of known medications that work instead of handling them directly?

Posted by Robert Savannah on 29 Mar 2011


Well it is a torpor issue that causes the bats to die off during the winter torpor. They do not have a sufficent supply of energy, for them to go back into torpor, after getting awoke by the fungus. They have a limited supply of energy for the torpor season, and would not be able to feed since it is winter...no insects available. The major cost for torpor is when you begin to come out, so if a bat is disturbed when in torpor and it awakes, a huge energy cost is incurred. If this happens 2 or 3 times during torpor season, then the bat eventually runs out of energy, and cannot go back into torpor.

Posted by C. J. on 30 Mar 2011


It may be a problem with torpor, but it's more likely that the fungi attacking their systems mess up the electrolyte balance. In the rainforest, the same things happen to tree frogs and they die of heart attacks. Probiotics solve the problem, but how do we treat them in the field?

http://news.nationalgeographic.com/news/2008/04/080401-frog-fungus.html

Posted by Beth Martell on 05 Apr 2011



 

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