As Bats Begin Hibernation, Deaths Expected

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As Bats Begin Hibernation, Deaths Expected

By Jessica Marshall, News.Discovery.com
November 2009

Why should we care about the fuzzy little flyers? Somewhere between 20 and 25 percent of all mammalian species in the U.S. are bats.

It won't be long before millions of bats settle into caves and mines across the country to hibernate. But the sad truth is that many in the East will never see the warmth of spring.

More than a million bats have died so far from white-nose syndrome, a still-mysterious bat killer that has spread throughout the Northeast and into Virginia and West Virginia, since it was first detected in New York in 2006.

Experts will be waiting to see how far the syndrome advances this winter. They fear it may make it into Kentucky and Indiana, where most endangered Indiana bats live in fewer than 10 caves or mines.

Why should we care about the fuzzy little flyers? Somewhere between 20 and 25 percent of all mammalian species in the U.S. are bats, according to Hazel Barton of the University of Northern Kentucky in Highland Heights.

The average bat eats 600 insects a night. With more than a million bat deaths last winter, 693 tons more insects buzzed and fluttered around the white-nose syndrome's range this summer, including moths that act as crop pests and mosquitoes that can carry West Nile Virus.

"If we lose the bat population in North America," Barton said. "Everyone will notice."

The outbreak recently prompted the U.S. Fish and Wildlife Service to award $800,000 in grants to explore the cause and control of the rampant disease. Exactly how the bats die is not yet certain, but it appears that a cold-and-damp-loving fungus infects the bats' noses and wings while they hibernate, dusting their muzzles and wings powdery white.

"The bats are almost at the ambient temperature of the cave. Their immune response is almost nonexistent," said U.S. Fish and Wildlife Service biologist Jeremy Coleman, who heads the agency's white-nose syndrome programs. "They're like sitting ducks."

Bats normally waken from hibernation anywhere from every week to every few weeks, depending on the species and conditions. They heat themselves back up to normal temperature, groom themselves, fly around and then settle back into hibernation.

Researchers do not know why the bats do this. They may need water, or to shed waste. One idea is that they fire up their immune systems during their arousal period to scan for threats.

Although these arousals only happen a few times during the winter, they take a lot of energy -- perhaps more than 80 percent of the bats' fat stores.

Infected bats have more frequent arousals -- as often as every few days. "We don't know why they are aroused more frequently -- if it's itching or agitation or if it is something they're detecting," Coleman said.

These extra arousals may cause the bats to exhaust their fat stores far too soon.

"Bats are leaving the sites in the middle of winter," Coleman said. "Are bats starving and going out looking for food? That's what most people are saying. There is some evidence that these bats aren't actually starving when they go out on the landscape. Maybe they are agitated and have recognized that there is a problem with the site. Maybe they're looking for somewhere else to go."

Other unknowns include when and how the disease spreads from cave to cave and bat to bat. It may be that the bats transfer it to new caves when they swarm together in fall. They may also transfer it during the summer, but the fungus is intolerant of warm temperatures, so that is less likely, Coleman said.

Some bats survive the infection, perhaps because they were infected late in winter and therefore had the reserves to make it to spring. But many of these die in spring from an inability to forage successfully for food because the fungus has damaged their wings.

The sweeping lethality of the disease over just four winters makes extinction a real risk.

To protect against this possibility, the National Zoo will establish a captive population of Virginian big-eared bats, an endangered subspecies of big-eared bat, as a security population.

Few places have kept insectivorous bats in captivity, so the work will be a challenge, said Nucharin Songsasen, who is heading the project at the Zoo's Conservation and Research Center in Front Royal, Virginia. "But if we don't do anything there is a chance that this species will go extinct within a couple of years," she added.

In Vermont, researchers are reintroducing bats into caves whose bat populations were wiped out by the syndrome to see how long the fungus persists and whether caves can be successfully re-colonized.

Meanwhile, Barton, of the University of Northern Kentucky, is testing a plant-based antifungal compound to see if it can be used to kill the white-nose fungus in caves and on bats without wiping out the critical fungal communities that form the foundation of cave ecosystems.