AUDIE CORNISH, HOST:
Cave-dwelling bats have been dying by the millions across the U.S. and Canada. Experts blame white-nose syndrome. It's a fungal disease. Field biologists, though, are testing some promising treatments. Jacqueline Froelich of member station KUAF takes us now to a test site in the mountains of Arkansas.
JACQUELINE FROELICH, BYLINE: Wearing white hazmat suits, helmets and hip waders, Blake Sasse and Shawn Thomas cross a frigid rushing creek to the entrance of a manganese mine abandoned a century ago.
SHAWN THOMAS: And at some point after that, bats decided to move in and hibernate here.
FROELICH: Thomas works for Bat Conservation International, and Sasse is a wildlife biologist with the Arkansas Game and Fish Commission. They switch on their headlamps and slosh into the mine filled with knee-deep murky water. The ceiling and walls sparkle with condensation. Sasse counts what looks like tiny, furry brown bears clinging to the rock.
BLAKE SASSE: OK. We've got a couple of tri-colored bats on the wall right here, and they're both kind of covered with white frost.
FROELICH: The hibernating bats appear healthy, but in 2015, this colony was infested with a contagious white fungal pathogen.
SASSE: We had nearly 1,400 bats that particular winter, and then the following time we surveyed, it was down to six.
FROELICH: The irritating fungus, called Pd for short, spreads over bats' muzzles and wings, disrupting winter hibernation. With no insects to feed on, bats can starve. Deeper into the Ouachita Mountain mine, Thomas and Sasse unlatch a bat barrier to their treatment site.
THOMAS: And the idea is to clean the environment, and by environment, I mean the hibernaculum here where bats hibernate as a strategy to survive the winters.
FROELICH: Last fall, the team tried two treatments to combat Pd. They applied polyethylene glycol, a fungicide that doesn't harm the environment, and also used bursts of blue disinfecting ultraviolet light on uncertain marked places along the walls and ceiling.
THOMAS: And then we're going to be swabbing to test if Pd is still here and at what level.
FROELICH: The treatments are being replicated in two other remote, contaminated mines in Alabama and Ontario, Canada.
THOMAS: And that's really important because as we hopefully expand these treatments to other sites, we want to make sure it doesn't have other effects on the other critters on the cave walls like bacteria and invertebrates and especially bats and other mammals that use these places.
FROELICH: Jeremy Coleman is white-nose syndrome coordinator with the U.S. Fish and Wildlife Service. He says more than 6 million bats have died over the past decade, placing some species at risk.
JEREMY COLEMAN: Such as the little brown bat, the northern long-eared bat and the tri-colored bat. Those declines in many cases in excess of 90 percent for winter populations have continued to be observed through the Midwest and the southeastern U.S.
FROELICH: Coleman says scientists are also testing vaccines and probiotics to help bats build immunity to the fungus. That's important because bats consume insects that harm agricultural crops. The team will return here this spring and early summer to take more swabs. If successful, the entire mine will be treated. And if that works, Thomas says, the methods could be used on other hibernating bat ecosystems across North America.
THOMAS: It would be a one-time treatment in the late fall before hibernation starts.
FROELICH: Cleansing bad habitats of the fungus will work to reduce bat-to-bat transmission and re-establish declining bat populations. For NPR News, I'm Jacqueline Froelich in Fayetteville, Ark.
(SOUNDBITE OF TYPHOON'S "BELLY OF THE CAVERN")