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Some bats show resistance to deadly white-nose syndrome

“It’s still going to take a long time to get them back”

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Eight years ago, white-nose syndrome, a deadly bat disorder, spread from upstate New York and claimed its first victims in Pennsylvania. DeeAnn Reeder, a Bucknell University biologist researching the problem, was worried about bats’ chances against this fast-moving fungal scourge. “If you ask me on a really pessimistic day,” Reeder told City Paper in 2009, “I might say that we won’t have any bats in Pennsylvania in five years.”

Reeder’s 2009 prediction wasn’t far off. Take the little brown bat, historically the state’s most populous species, once numbering in the millions: Its ranks have shrunk by an estimated 99 percent or more. Other species, including the tri-colored, northern long-eared and Indiana bats, have been similarly decimated. Nationally, estimates the U.S. Fish and Wildlife Service, white-nose syndrome has killed about six million bats. And white-nose is still spreading. It currently infects bats in 31 states and five Canadian provinces — it’s even jumped to the Pacific Northwest — and there’s no known treatment.

But if all that sounds hopeless, it’s not, quite: In Pennsylvania and other states where white-nose struck early, bat populations have apparently stopped declining. “We’ve reached a relatively stable point, we think,” says Reeder today. For example, while the little brown bat’s numbers remain perilously low, remnant adults have now survived several years of white-nose and continue reproducing, suggesting they have in-born resistance or have otherwise adapted. And at least one other species, the big brown bat, barely seems to be affected by white-nose, Reeder says. Whether affected species can recover enough to survive long-term is uncertain. But for now, says Reeder, “We’re cautiously optimistic.”

White-nose appeared in North America in 2006. It’s caused by a cold-loving fungus (Pseudogymnoascus destructans) that dusts the muzzles and wings of hibernating bats. The infection, which is spread bat to bat by these highly sociable creatures (but is harmless to humans), makes bats arouse too often. That depletes their fat reserves; in winter, unable to feed, they die.

This has been bad news for more than the world’s only true flying mammal. Bats are also champion insect-eaters — a single bat can eat up to its weight in bugs in a night — and pollinators and seed-dispersers, too. They’re crucial to their ecosystems. And the authors of a 2011 report in Science estimated that bats save U.S. farmers $22.9 billion a year in prevention of pest damage and reduced pesticide application alone. 

Bats face other human-caused threats. For years they’ve been harmed by people disturbing their roosts (including those man-made bat caves: abandoned coal mines), by habitat loss and by pesticides. And in the past decade or two, bats have met a new enemy: wind turbines. One estimate cited by Bat Conservation International attributes as many as 400,000 bat deaths in the U.S. and Canada to wind turbines in 2012 alone. Worldwide, wind turbines are actually the single biggest killer of bats; wind turbines hit hardest migrating bats, who because they don’t hibernate are generally spared white-nose.

Conservation groups have been working with the wind industry on fixes like briefly idling turbines during periods of light wind, when bats are most active, reducing mortality while impacting energy generation minimally. Such efforts are a work in progress (there’s disagreement about the ideal wind-speed cut-off point), but bats’ biggest threat around here is still white-nose. While wildlife officials work to restrict human access to caves to help prevent its spread, researchers explore possible treatments for the disease. So far, though, most of the hope is coming from the bats themselves.

Bucknell’s Reeder, for example, is amazed by the how big brown bats resist the ill effects of the fungus that merely taints them while killing their cousins. “I’ve just started calling them the superbat,” she quips. The big brown’s larger body size helps (it’s got more fat to burn if it wakes up early), as do its habits of hibernating in colder, less crowded roosts for shorter periods of time. There’s some evidence that remnant little brown bats, too, have taken to colder roosts, where the fungus doesn’t thrive. Genetic factors are also being researched, she says. Christina Kocer, the U.S. Fish and Wildlife Service’s northeast-regional coordinator for white-nose syndrome, notes that ideally, bats who’ve survived white-nose have a resistance they can pass on to their pups.

Perhaps North American bats will follow the path apparently taken historically by bats in Europe and Asia, where Geomyces destructans is endemic but somehow rendered harmless. (The fungus was likely imported here inadvertently from Europe, by humans.) Yet even if the worst of white-nose is over in Pennsylvania — a big “if” — bats face a struggle. They live 20 years or more in the wild but reproduce slowly: Big brown bats are the only species in Pennsylvania that bear even two pups per litter, says Reeder. 

Kocer, who’s based in Massachusetts, says bat populations in New York and Vermont are stabilizing, too, even growing. But even if all goes well, she says, “It’s still going to take a long time to get them back.”

[Editor's note: This article has been edited to accurately reflect the scientific name of the white-nose fungus and the number of Canadian provinces where white-nose has been detected.]

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