White nose syndrome: Bats showing signs of resilience

DORSET, Vt. – Deep in a cool, wet cave in Vermont, tens of thousands of chocolate brown furry creatures squirm.

Little brown bats who survived a deadly mushroom decimated their population, going into hibernation last fall. Now that it’s early May, they’re waking up, leaving their rock wall shelters and making their first test flights in search of the moths, beetles and aquatic insects they feed on.

It was here, in the deep passages that crept into the mountains of Vermont, that scientists found one of the first outbreaks of the fungus that causes white nose syndrome in North America. Bat bones were scattered on the floor of the cave like pieces of hay. Look closer and you’ll find a small skull.

And the bats are still dying.

White nose syndrome is caused by an invasive fungus that was first found in a cave in upstate New York in 2006, a short flight of bats from Dorset colony, Vermont. This fungus awakens bats from hibernation, sending them into the cold winter air in search of food. They die from exposure or from starvation because insect populations are too sparse to support them at that time of year.

Smaller than a mouse and weighing about three pennies in the hand, Dorset bats glide through cave walls or cling to each other for warmth. Their health suggests that at least some species are adapting to the fungus that has killed millions of its brethren across North America.

“That’s really important, because it seems to be a stronghold where these bats mostly live,” said Alyssa Bennett, a small mammal biologist with the Vermont Fish and Wildlife Service. survived and then spread throughout New England. She has been studying bats and white nose syndrome for over a decade.

“We hope that is the source population for them to recover,” Bennett said as the creatures hovered and swooped around her.

It will take time. The little brown female bats give birth to only one calf per year. And although they can live into their teens or 20s, only 60 percent to 70 percent of the pups survive the first 12 months, says Bennett.

Scientists currently estimate that between 70,000 and 90,000 bats hibernate in Dorset Cave, the largest concentration in New England. Their numbers have dwindled from an estimated winter population of 300,000 to 350,000 or so in the 1960s, the last time the site was surveyed before the white-nosed invasion.

It’s not clear how much the numbers dropped after the fungus entered, but biologists who visited in 2009 or 2010 noted the ground in front of the cave was covered with bat carcasses.

The fungus that causes white nose syndrome is thought to have been brought to North America from Europe, where bats seem to have gotten used to it. Named for the translucent, white spots it produces on the nose and other parts of the bat’s body, the fungus has killed more than 90% of bat populations in parts of North America.

Last month, a report by the North American Bat Conservation Coalition found that 81 of the 154 known bat species in the United States, Canada and Mexico are at serious risk from white-nosed infections, climate change, and habitat loss.

It is important. The U.S. Geological Survey estimates that bats boost U.S. agriculture by $3.7 billion a year by eating crop-destroying insects such as caterpillars that lay larvae, which their offspring carry onto corn crops. .

Scientists have known for many years that some species of small brown bats seem to survive exposure to this fungus, although the overall mortality is thought to be able to destroy them. While Dorset’s little brown bats are holding on, Bennett said, other species that were once common with them, such as the northern long-eared bat or the tricolor bat, are now nearly undetectable, Bennett said. there.

“There’s something special about those bats,” Bennett said of Dorset’s little brown bats. “We can’t say exactly what that is, but we do have genetic studies we’ve collaborated with that show those bats have factors related to hibernation and immune responses that allow them to tolerate can tolerate the disease and pass those traits on to humans. for their young people.

Winifred Frick, chief scientist at Bat Conservation International, who has tracked the evolution of white nose syndrome across North America, said the fungus has been found in 38 states to date. She says it’s a “smash to the heart” every time she hears about a new outbreak.

Colorado reported its first infected bats earlier this year.

Frick is relieved that bats are starting to breed again in some areas where bat carcasses were once piled up, even if the numbers recovered so far have been a fraction of previous numbers.

“It was a real glimmer of hope,” she said.

In addition to Vermont, other areas near where the white nose was first discovered also report steady, possibly increased populations of small brown bats.

Greg Turner, the state mammal expert for the Pennsylvania Game Commission, said Pennsylvania lost about 99.9% of its population after the white nose struck. While the numbers are still low, they are increasing in some places. An old mine in Blair County had just seven bats in 2016. This year, there were more than 330.

“I feel pretty comfortable,” Turner said. We won’t be stuck staring at the crater of extinction.”

His research shows that bats that hibernate in colder temperatures are better at fighting white-nosed disease because the fungus grows more slowly.

That could mean that bats are less likely to wake up from the stimulation it causes, although scientists still don’t understand the mechanism that allows some animals to survive while others do not. could not resist.

“By choosing colder temperatures, they’re helping themselves in two ways, they’re helping them conserve fat and conserve energy, and they’re also less likely to get sick,” says Turner.

However, there are still worrying trends. Pennsylvania’s bat population is a fraction of what it was before the invasion of white-nosed bats. In some locations, Turner and his colleagues saw more bats, but somehow fewer females.

In Virginia, the population has plummeted by more than 95%, although the state is beginning to see some colonies stabilize or slightly increase their numbers. However, that’s only happening in a fraction of the sites that have ever been monitored, said Rick Reynolds, a non-game mammal biologist with the Virginia Department of Wildlife Resources.

“We remain optimistic, but there is a long way to go with many uncertainties,” Reynolds said in an email.

Back in Vermont, where the temperature in Dorset Cave falls around 40 degrees Celsius (about 4.4 degrees Celsius) in winter, the bats seem to have found a suitable spot cold enough to slow the growth of the bats. mushroom.

Bennett is working with Laura Kloepper, a bioacoustic expert from the University of New Hampshire, to better handle population numbers. Using acoustic modeling, they are working to get a baseline estimate of this year’s population by comparing audio recordings with thermal images. They will survey again using the same method next year to try to identify change.

“We wanted to try to understand what we could do to save not only the bats, not just the bats in this cave, but real bats around the world,” Kloepper said.