A bunker once used to store nuclear weapons in northern Maine became home to 30 bats struggling for survival last winter when the Aroostook National Wildlife Refuge joined the country’s battle against white-nose syndrome. Researchers are attempting to better understand the disease that is killing these cave-dwelling bats in such record numbers — the most dramatic die-off that’s been seen in North America in the past century and perhaps in recorded history.

“The bunkers actually mimic caves within the state of Maine to a very similar degree,” said Steve Agius, assistant manager of the Limestone refuge, which is home to 43 military bunkers of the former Loring Air Force Base.

The experiment — a component of the U.S. Fish and Wildlife Service’s plan for managing white-nose syndrome — was to study if artificial, sterilized hibernacula can be used to increase survival rates of bats infected with the disease.

Roughly 500 abandoned bunkers are located on U.S. Fish and Wildlife Service property, but only the Aroostook County bunkers were cold and humid enough to mimic the caves and mines where bats hibernate.

“Unfortunately, the population of little brown bats in the state of Maine has dropped so dramatically that we weren’t able to get bats within the state,” Agius said. “New York and Vermont each donated 15 little brown male bats to the project.”

The bats were transported to Maine in December 2012 and released in “Bat Bunker No. 1,” a cavernous concrete dome built into a grassy hillside. Agius remembers hanging the sleeping bats “like Christmas ornaments” on a felt blanket that was hung in the bunker. Soon after, the bats woke and congregated in a tightly-packed group high up on the cement wall.

“The bats responded in a very favorable way to being in the bunker here,” said Agius, who traveled to the bunker by snowmobile throughout the winter to monitor the bats’ behavior on a computer in the bunker’s front room. He viewed the winged creatures using infrared motion-activated cameras in the main chamber so he wouldn’t disturb them.

“I wanted to make sure they were behaving naturally,” Agius said. “If they weren’t, we would collect them and bring them back to the caves [in New York and Vermont].”

Agius observed the bats waking every now and again to drink water from pools on the floor — natural behavior for hibernating bats. Nevertheless, just nine of the 30 bats survived the winter. In late March, biologists collected the bats, evaluated their conditions and transported them to their original caves.

“Nine of 30 bats surviving is not great,” Agius said. “But it still shows there is a potential for having successful artificial hibernacula in the future.”

The spread of the disease

Since first discovered in 2006 in a cave in Schoharie County, New York, white-nose syndrome has wiped out 75-90 percent of the little brown bats in New England. The disease has spread rapidly to 22 states and five Canadian provinces, killing an estimated 7 million bats.

The disease thrives in damp, cold environments, such as the caves and mines in which some species of bats choose to hibernate. In addition to the little brown bat, 10 other cave-hibernating bats are at risk of white-nose syndrome, according to whitenosesyndrome.org.

Little brown bats, formerly the most abundant species in the U.S., are being severely impacted by the disease.

“In all good likelihood, the population of little brown bats will never get back to what it was in our lifetime,” Agius said. “They just don’t have the reproduction rate that would allow their population to increase exponentially.”

A long-lived species, little brown bats as old as 30 years have been found in the wild, according to the Ohio Division of Wildlife, and they only produce one to two pups a year.

Maine’s last cave becomes infected

Maine appeared to be insulated from the disease until spring 2011, when biologists found white fungus growing on bats in two caves in Oxford County. Since then, three bat species in Maine — little brown bats, northern long-eared bats and eastern small-footed bats — have seen somewhere between 80 and 100 percent declines in their populations due to white-nose syndrome, according to John DePue, wildlife biologist with the Maine Department of Inland Fisheries and Wildlife.

“Unfortunately for a lot of states, including Maine, this disease came on so fast and was so impactful that it wasn’t until the white-nose syndrome was on our landscape that we started to collect data on the most abundant species of bats in North America,” said DePue.

This summer, DIF&W biologists will collect acoustic data of bats for the third year in an effort to estimate Maine bat species populations.

In addition to the two infected hibernacula in Oxford County, Maine biologists know of only one other major hibernacula in the state — a cave located near Allagash Lake that typically houses 45-60 bats, both little brown bats and northern long-eared bats.

The Allagash Lake cave remained free of the disease, housing fungus-free bats, during winter 2011-12, even though white-nose syndrome had infected surrounding hibernacula. But this March, DePue made a sad discovery.

Huddled and clinging to the rock of the cave were nine hibernating little brown bats — their furry bodies about the size of baseballs — and the telltale white fungus of white-nose syndrome was growing on their muzzles and wings.

“I was hoping we would just keep it clean for years, but we knew it was a matter of time until it was going to be infected,” DePue said. “I’m kind of surprised it held out as long as it did.”

How the deadly fungus works

White-nose syndrome was given its name because of the white fungus, Geomyces destructans, that grows during hibernation on the noses, wings, ears and tails of most infected bats.

The fungus causes bats to wake and fly around, expending more energy than usual during the winter, when the small animals rely on meager fat reserves to survive. This disruption often causes bats to expend too much energy and starve. Sometimes, bats will leave the shelter in search of food and freeze.

Biologists also have seen cases where the fungus has eaten the skin away from bats’ wings, rendering them incapable of flight, their only true mode of transportation. Little brown bats not only eat while in flight, catching a variety of insects, they also drink by flying just above the water’s surface, according to the Adirondack Ecological Center.

In Bat Bunker No. 1, the 21 bats that died had severe damage to their wing membranes, while the surviving bats had less skin damage.

While biologists are still learning about white-nose syndrome, they believe that the disease is transmitted from bat to bat, and there is also circumstantial evidence that humans can carry white-nose syndrome from infected sites to clean sites.

Farmers will miss the ‘flying mice’

While bats have long been thought of as pests, “flying mice” with a propensity to break into attics, they’re an important part of the ecosystem, as well as the economy.

The number of insects consumed annually by one million bats is just less than 700 tons, according to Bat Conservation International. And since many of the insects eaten by bats are crop pests, their loss likely will have expensive impacts on agriculture. A 2011 study published in Science magazine estimates that insect-eating bats save the U.S agricultural industry at least $3 billion a year.

“A lot of the general public are afraid of bats for some strange reason that I can’t begin to guess because I’ve been a fan of bats for a long time,” DePue said. “As a kid, I used to watch the bats come and eat the insects at all the lights of my house.”

One bat can eat up to 1,000 moths, beetles or mosquitoes per night, according to the DIF&W.

“Some people think that they dive bomb their head,” DePue said. “But if a bat is flying anywhere near you, you should thank that bat; it’s eating the insects that are about to bite you.”

The search for a solution

“There’s no established treatment for getting rid of the fungus,” Agius said, but an extensive network of state and federal organizations are researching white-nose syndrome to develop strategies to minimize its impacts.

Sterilizing caves to slow the disease’s progression has been ruled out because researchers don’t want to damage sensitive and complex cave ecosystems. This leaves the option of creating artificial hibernacula, such as modified bunkers, that can be sterilized.

“It could give them a little bit of a chance,” DePue said. “Some people thought that it was kind of a crazy idea, but we’re kind of desperate right now, and crazy ideas can be entertained. It had some positive results, and it may just have to be used in the future.”

A part of that research is comparing North American bats to European bat species.

“They have the fungus [in Europe], and it just doesn’t kill the bats like it does in North America,” DePue said.

There is a theory that the fungus may have initially entered North America on the gear of people visiting caves in Europe.

“There’s hope that some individual bats have some genetic resistance to white-nose [syndrome],” DePue said. “There is a lot of research taking place right now to try to determine if there are individuals that carry antibodies.”

Back to the bat bunker

Bats will not be transported this winter to Maine’s Bat Bunker No. 1. Instead, Agius is planning to try to naturally attract migrating bats to the bunker by broadcasting swarming calls that bats use to congregate for hibernation from solar-powered high-frequency speakers.

“We’re hoping that if they do choose to hibernate here that their survival rates will be higher than in a cave because the fungus will not be present here, and then every year we will go in and sterilize the bunker,” he said. “That’s the anticipation.”

For information on white-nose syndrome in Maine, visit mefishwildlife.com. To learn about white-nose syndrome nationally, visit fws.gov/whitenosesyndrome or whitenosesyndrome.org.

Aislinn Sarnacki is a Maine outdoors writer and the author of three Maine hiking guidebooks including “Family Friendly Hikes in Maine.” Find her on Twitter and Facebook @1minhikegirl. You can also...