Shrouded in folklore, spooky campfire tales and hyperbolized cinema, bats can seem elusive, mysterious and even threatening. But in recent years, a deadly fungal disease has wreaked havoc with bat populations nationwide. In caves and mines in the northeastern United States, “We have seen 90 to 100 percent mortality,” says mammalogist Katherine Caldwell of the N.C. Wildlife Resources Commission. Since 2006, white nose syndrome has been found in 31 U.S. states and five Canadian provinces, killing millions of bats. “Every winter we have more and more states added to the list. Last year was a big shock, because it spread all the way to Washington state — and about 1,300 miles from the previous westernmost detection.”
In North Carolina, nine of the state’s 17 species have been decimated, mostly here in the mountains. “It’s not all of our bats, but it’s some of our most common ones, like little brown bats,” Caldwell explains. “So even though we’re not losing a whole bunch of species, we’re losing a whole bunch of individual bats.”
Bats, she notes, play a major role in their local ecosystems, “from being pollinators to seed dispersers. Here in North Carolina, our bats are all insectivorous — they can eat their body weight in insects in one night. Insects have their own merits, but if any link in an ecosystem goes unchecked, the whole thing can get out of whack, especially for crops and forest health.”
That translates into a major economic impact. According to the U.S. Geological Survey, loss of bats could cost North American agriculture more than $3.7 billion per year. And in Western North Carolina, where most of the state’s bat habitat is found, a small, passionate community of biologists and other researchers is collecting data and working to preserve the area’s remaining bat colonies.
One large Haywood County mine that’s been monitored for years illustrates the scale of the die-off. In 2011, says Caldwell, “The site had close to 4,000 bats; this winter there were only 30. Those are the kind of declines we’re seeing here. You have to be an optimist to work with bats these days, because it can really get you down.”
On the nose
The name white nose syndrome is quite literally on the nose. “It grows on the face, the muzzle, the forearms, the wings; really any nonfurry portion of the bats,” notes Caldwell, adding that the microscopic fungal spores don’t become a deadly disease until they grow into the bat’s tissue. The fungus thrives in the environments where bats tend to hibernate, such as caves and mines.
First recorded in Howe Caverns in New York state in 2006, the disease made its way to WNC five years later. “We think it’s native to either Europe or Asia,” says Caldwell. “Very similar strains of the fungus are found across Europe and Asia, though the bats there don’t seem to show these massive mortalities like we’re seeing.”
The microscopic spores, she explains, “are pretty hearty. They’ll stick around on your clothes, your shoes or equipment and can be transported from place to place. Maybe someone went caving in Europe or Asia and, unbeknownst to them, eventually came into Howe Caverns and accidentally inoculated it. Bat fur or hair can also carry the spore, so in North America, we think it’s mainly been spread by the bats themselves.”
To prevent further contamination, says Caldwell, researchers “take major precautions not to spread it ourselves, since we go everywhere the bats are. We dress in Tyvek suits when we go in the caves and mines in the winter; in the summer we wear scrubs over our clothes and latex gloves.”
Caldwell and her colleagues use various types of surveys to gather data. There’s also a citizen science project. “Folks drive a 20-mile route that we’ve given them,” she explains. “They have an acoustic detector mounted on the roof of their vehicle that will record bat echo location calls as they’re driving down the road. Year by year, we’re able to see the change in those numbers of bats or bat calls across the mountains.”
This summer, notes Caldwell, she’ll participate in about 20 mist-netting surveys. “We usually get to our site around 6 or 7 p.m. and set up two to four mist nets. They’re around 20 feet tall, set between two vertical metal poles so that bats will accidentally fly right into them, and we can just pick them out of the nets. We’ll write down what species it is, whether it’s male or female, adult or juvenile, if a female is pregnant or lactating. Then we put a little metal band on the bat that has a four-digit code, so if we ever recapture it we’ll have some sort of survivorship and age information. We stay out until 1 or 2 a.m., and then we clean everything up and literally decontaminate everything we use.” The results of these studies, she says, can help drive home to policymakers and the general public the urgency of maintaining healthy bat populations.
The long road to repopulation
Bats are relatively slow to reproduce. “People are always surprised by how long bats live,” says Caldwell. “I think the oldest little brown bat found was about 32 years, and they’re only 7 or 8 grams. People often think they’re analogous to a rodent but they’re really not, since rodents have these supershort life spans and reproduce exponentially. Bats have a long life span and usually produce only one pup a year, so they’re more like us. That’s why white nose is so hard on the populations: To recover from these hits is going to take a really long time.”
In the meantime, Caldwell and other researchers are finding hope on two fronts: natural resistance and ways to kill the fungus. Kendrick Weeks, the Wildlife Resources Commission’s western wildlife diversity supervisor, says that elsewhere in the state, “There are small pockets of healthy colonies of different species. That may indicate resistance, seasonality and/or some other factors are involved in the localized increase in survivorship.”
Over in the coastal plain, notes Caldwell, the N.C. Department of Transportation has been doing a lot of work with northern long-eared bats. “They’re able to catch these bats in the wintertime, which means they’re out flying around, likely foraging, and so far we haven’t detected white nose in that area at all. So maybe we won’t lose the species altogether, and we’ll have some of these reservoirs.”
Sue Cameron of the U.S. Fish and Wildlife Service’s Asheville field office notes, “There are many scientists from around the world working very hard to develop treatments to help our bats. Much progress has been made, and while treatments are not expected to eliminate the fungus, we’re hopeful they’ll buy bats some time to develop resistance, especially in locations that are only just starting to feel the impacts of this devastating disease. Treatments are in various stages of development, with some being field-tested now.”
At this point, however, North Carolina has so few bats left that it may be harder to save them. In addition, stresses Caldwell, it’s a highly complex situation: Before using any treatments that researchers come up with, she explains, “There are just a lot of decisions you’d want to make, because part of it is wanting to understand how they will affect everything else in that system. There’s native fungi underground, there are insects, there’s runoff and water systems to consider. Time will tell what the best solution is, but it may just be to let these populations very slowly recover while we try to aid in their conservation as best we can and provide good habitat for them.”