When the bats leave the belfry: Fungus cuts down bat population, sparks speculation on species, ecosystem future
Sarah Davis loves bats. They’ve been the wintertime residents of Linville Caverns for as long as she can remember, a marker of the seasons she looks forward to each year. The cave, a commercial cavern near Marion, has been in Davis’ family since the 1940s — she and the bats go way back.
“There would be hundreds of them in the winter, and I absolutely loved them,” Davis recalls.
But the biologists who were climbing out of Tyvek suits and pulling off thick-walled rubber gloves as she spoke are afraid those memories might remain forever in past tense. Bat populations across the eastern United States have taken a nose-dive in recent years, all at the hands of a mysterious fungus that since 2006 has slowly made its way from a single cave in Schoharie County, New York to appear in 25 U.S. states and five Canadian provinces. In 2011, it arrived in North Carolina.
“When I started telling them [my staff] about it, it upset me so much I started crying,” Davis recalled.
This year, biologists counted just seven bats in the cavern, a far cry from the 95 they found in 2006, five years before white-nose syndrome, the disease the fungus causes, was found in North Carolina.
The numbers were low enough that Sue Cameron, wildlife biologist with the U.S. Fish and Wildlife Service, wasn’t even sure if there’d be enough in Linville Caverns to warrant data collection for the University of California study North Carolina is contributing to.
“If I can’t get three of one species, I probably won’t swab,” she told Katherine Caldwell, the N.C. Wildlife Resources Commission biologist who conducted the cave survey with her.
Let sleeping bats lie
Finding bats in Linville Caverns was like seeking out the proverbial needle in the haystack. Mica and fool’s gold glittered in the dimly lit walls, smooth limestone formations gleamed with moisture and an underground stream chattered alongside the concrete walkway as Caldwell’s and Cameron’s headlamps searched the cave’s many nooks and crannies, hoping to spot something tiny, furry and alive. Last week, staff had found just six bats, manager Andrew Quinn told the scientists.
Finally, one of the little mammals appeared, a tri-colored bat hanging from the ceiling. Caldwell noted the bat and its species on her tally sheet, and Cameron got out her sampling supplies. North Carolina is gathering data for a University of California researcher, Winifred Frick, who’s trying to learn more about where the fungus causing white-nose exists and how it’s transmitted.
Gathering data for the study involves breaking the surveyors’ cardinal rule: thou shalt not wake the bats. Rousing during the winter months eats up valuable energy, burning through the fat reserves on which the bats must survive until springtime brings back the insects.
But white-nose syndrome is still a little-understood disease — the fungus, which scientists postulate originates from Europe, was new to science when it first showed up in New York — and the first step in quelling the dizzying rates of decline in affected species is knowing more about how it works. It’s an all-hands-on deck sort of situation.
“It’s amazing the amount of research that’s going on, and it’s coming out so quickly,” Cameron said.
She pulled out a measuring tape, taking samples from rock surfaces 10 centimeters and 2 meters away from the sleeping bat. Then she aimed at the bat with a yellow tool resembling a hybrid between a laser pointer and a drill, calling out the resulting body temperature reading for Caldwell to record. Finally, she set up a ladder and ascended to stroke the bat’s body, gently but firmly, with a scientist’s version of a q-tip. The bat wriggled, letting out a squeak like a fussy newborn. Cameron deposited the swab into the open container that Caldwell had waiting, and the pair rapidly moved themselves and their equipment away, letting the bat settle back to sleep as quickly as possible.
Toward the mouth of the cave, the numbers had seemed somewhat promising, with bat findings coming in close succession and only one of the animals showing the telltale dusting of the white-nose fungus around its snout. But as the group traveled deeper into the cave, bat sightings ceased. It’s hard to say for sure — hibernation behavior varies with the specific cave and type of bat — but that’s probably atypical, Cameron said.
“We’ve seen some odd behavior as a result of white-nose syndrome,” she said. Such as bats sticking closer to the mouth of the cave than they otherwise might, taking daytime flights during the winter or waking up more frequently than usual during hibernation.
“It’s pretty complex.”
The group finished scouting the cave passages, and Cameron switched out the little device recording cave temperature and humidity, another contribution to Frick’s study, with a fresh one. The entire survey took only about an hour, a good bit shorter than in previous years.
“Now we’re not having to spend the time, sadly, counting a lot of bats,” Caldwell said.
A rising death toll
Of course, it’s hard to tell a whole lot just from the results of one cave, and that’s been one of the main questions ever since white-nose hit: Are the bats actually disappearing, or are they just changing their habitats or using different caves? The jury has reached an unfortunate verdict, Cameron said.
“All the evidence is showing the same thing, and that’s that these declines are happening,” she said.
The Wildlife Commission has done counts of hibernating bats since well before white-nose syndrome hit. Every year, they sample a different set of caves and mines in Western North Carolina, the goal being to accumulate a hefty dataset without disturbing the same caves year in and year out. Since the fungus came to WNC in 2011, the declines have been staggering.
“People weren’t totally sure how it would play out in the southern states,” Cameron said. “I think people were hoping things would be a little bit different and bats would respond differently in Western North Carolina, and so far that hasn’t been the case.”
Just like in the northeast, southern bat populations have crashed, and crashed hard.
For example, a mine on Waynesville town property had pretty consistent counts of 3,000 tri-colored bats before white-nose syndrome arrived. This year, Caldwell counted nine. Another cave, located on Nantahala National Forest property near Nantahala Outdoor Center, housed 1,073 bats when it was last counted in 2013, a tally reflecting only small white-nose impacts. But the quadruple digits didn’t last — this year, biologists counted just 58 bats there. The crash is evidence of white-nose’s spread south, Caldwell said. Currently, the fungus has been spotted in 10 North Carolina counties.
Since white-nose’s arrival in WNC, little brown bat populations have dropped an estimated 92 percent, according to counts from summer captures, with that number sitting at 78 percent for northern long-eared bats and 77 percent for tri-colored bats. Numbers are still trending down, Caldwell said, but there’s some evidence the death toll could be leveling off.
For example, in one Haywood County site whose bat count had dropped from 4,000 in 2011 to 55 in 2014, 30 bats were found this year. That’s still a hefty decline, but it’s a gentler rate than what’s been observed before now. Similarly, an Avery County site that housed 17 bats last year revealed 15 in 2015 — virtually the same number, as counts are more an indicator of population levels than an exhaustive census of every bat hiding in each remote corner of a given cave.
“Mostly what we just saw were small declines in hibernacula [bat caves] that had already experienced sharp declines and also steady numbers after sharp declines,” Caldwell said.
Another good sign, she added, is that none of the caves were devoid of bats and some of those bats were without visible signs of white-nose. That doesn’t necessarily mean they don’t have the disease, she clarified, but it’s at least encouraging to find bats that don’t appear sick. Maybe, just maybe, they’re actually able to remain healthy even after encountering the white-nose fungus.
“We’re hopeful that if there are a few bats year to year that maybe some resistance could occur and potentially be passed on,” she said, “but it’s hard to say right now.”
Absent in this year’s surveys, though, was the northern long-eared bat. The species has never been especially abundant in Western North Carolina, but it’s always been present. One of the hardest-hit species since white-nose came to roost, its numbers have suffered in other parts of the country as well, leading the Fish and Wildlife Service to list it as a threatened species April 1.
Holding out hope
The facts paint a grim picture for bats, but Caldwell isn’t quite ready to write the obituary.
“I’m reluctant to say they can’t recover,” she said. “I think I’m too much of an optimist to say that, and there are too many factors involved. I’d like to think that long after we’re gone, the bats are going to recover. It will be slow, slow recovery though.”
Bats are long-lived, slow-reproducing creatures. They can live as long as 40 years, with lifespans more commonly hovering around 20 years. They typically have just one pup per year, and the mortality rate for young bats is high.
Even if white-nose syndrome disappeared today, it would take a long time for bat populations to rebuild — assuming enough remain to find nearby mates and sustain genetic diversity.
But science isn’t a fully written book, Caldwell pointed out. There is still a lot we don’t know, and research turns up new information every day. For instance, a study out of University of North Carolina Greensboro detected northern long-eared bats — the ones the Fish and Wildlife Service just listed as threatened — living year-round on the coast without hibernating. Because of the environment the fungus requires to grow, white-nose syndrome infects bats only while they’re hibernating in caves, so no hibernation equals no white-nose mortality.
“There could be some remnant populations that may not be as hard-hit,” Caldwell said.
It’s also important to note that while white-nose is decimating populations of some of the most numerous bat species in the U.S., it doesn’t affect all of them. More than 40 bat species inhabit North America, about half of which hibernate, and white-nose affects only about seven.
Since white-nose was discovered, millions of research dollars have poured into defining and, hopefully, fixing the problem. But why? Why, aside from a passing preference to keep all the species around, is it so important to save the bats?
If you were to ask Aldo Leopold, a renowned conservationist who died in 1948, he might repeat one of his better-known quotes: “To keep every cog and wheel is the first precaution of intelligent tinkering.” That is, pieces of the natural world have inherent value because we don’t know all their functions. Like a nondescript screw fallen out of a bicycle in the workshop, an ecological puzzle piece is something you better keep around in case you wind up needing it later.
“We don’t know for sure what it means,” Cameron said when asked what declines in bat populations might portend for the ecosystem at large. “We’ve never been faced with anything like this before.”
The research is just getting going on this question, but white-nose certainly has the potential to deliver a blow to agriculture. Bats do a lot to control insect populations, with a single bat consuming between 3,000 and 6,000 insects per night. Favorite meals include moths, beetles and mosquitoes; collectively, bats eat thousands of tons of insects every year, many of them agricultural and forest pests.
“The concern is that this huge reduction in bat populations could result in an increase in these pests or some insect populations,” Cameron said.
A 2011 study by Justin Boyles of Southern Illinois University put the economic impact of the loss of bats in the U.S. at between $3.7 and $53 billion per year, with numbers based on the increased cost of applying pesticides on farmland to combat all the extra insects. The study did not account for the lost benefits of bat-controlled insect populations in forests or for the downstream environmental effects of increased pesticide use.
The study also assumes the complete disappearance of all bat species. But white-nose does not affect all bats. The fungus hasn’t been detected on tree-dwelling bats, and of those in WNC that hibernate in caves, Rafinefque’s bat and the Virginia big-eared bat — which is listed as endangered — don’t seem to be bothered by white-nose. The study points to other threats, such as death from windmills collisions, as the rationale for quantifying the impact of a total bat loss.
There are other variables, too. For instance, how might other species in the ecosystem adjust to accommodate for a dearth of bats?
“There could be an increase in some bat populations that aren’t impacted by white-nose syndrome and that might help make up for it,” Cameron postulated, “but we don’t really know.”
The effect of white-nose syndrome could be much less than feared, or it could be more.
Impacts for agriculture
The conclusion of this saga will have implications for the agricultural landscape of Western North Carolina.
This corner of the state is a bastion of local produce, agritourism and farming, adding more than 10,000 acres of farmland between 2007 and 2012 while acreage declined in the rest of North Carolina, according to the Appalachian Sustainable Agriculture Project. Bats can take some of the credit for those numbers. In their nighttime flights, the winged mammals eat extraordinary quantities of insects, many of which are pest species to agricultural operations. As shown in Boyles’ study, substituting pesticides for that natural predation could prove expensive.
But so far, the issue doesn’t seem to be much on farmers’ radars.
“The only calls I usually get about bats are about how to control bats that are problematic in their house,” said Christy Bredenkamp, horticulture agent for N.C. Cooperative Extension in Swain and Jackson counties.
Caldwell, too, said she hasn’t had any personal dealings with concerned farmers but would like to see agricultural and scientific communities continue forging relationships on this issue.
“It’s a tough industry, so I think if they were potentially more aware of what a benefit bats are and what it might look like if we lost most of our bat population, maybe they would be more open to doing things that would benefit bats,” she said of farmers.
Whole-ecosystem health is important, agreed Steve Beltram of Balsam Gardens, an organic farm in Jackson County. Building a healthy, balanced ecosystem on farmland is a central principle of organic farming, so from that perspective the decimation of any species is concerning. But while Beltram’s certainly heard of white-nose syndrome and its effects on bats, he hasn’t considered the issue as something that could affect his farm. And though bat populations have taken a nosedive over the past several years, Beltram hasn’t noticed any difference in insect levels on his farm.
“Nothing out of the ordinary,” he said of insect populations. “What seems to affect it more than anything else for us is whether we get a cold enough winter to kill off a lot of stuff, but I can’t say that I’ve noticed any pest issues more than any other times and certainly can’t attribute it to bats.”
In the agricultural sphere, declines in bat numbers are far from being an isolated variable. Farmers are contending with a host of other challenges to the lands they work — honeybee shortages and colony collapse disorder, for instance. Between 2006 and 2011, about 33 percent of honeybee colonies disappeared each year, a phenomenon which does not yet have any certain explanation but worries farmers, whose crops rely on bee pollination to bear fruit.
“Any kind of farmer is going to be equally affected by that, anyone who uses pollination,” Beltram said.
Still, Caldwell thinks that as white-nose progresses — if, in fact, it does — the fungus will push closer and closer to the forefront of issues demanding farmers’ attention.
“I think as more and more people learn about white-nose and learn about the threats that bats face, they would be thinking along those lines,” she said.
It’s still hard to tell exactly who will be affected by the bat decline. Will the white-nose-susceptible species disappear? Or will they somehow stabilize and recover? If they disappear, will insect populations skyrocket? Or will populations of other creatures adjust to feed on the abundant bugs? What about the animals that eat bats, the hawks and owls and snakes and fish? Will their diets shift somehow?
Sometimes, ecology is like a giant Rube Goldberg machine — each piece connected to another, the path from the initial shift in gravity to the final result nearly impossible to predict.
So, the knowledge-gathering continues. The counts of hibernating bats, the data collection for scientists in far-flung states, the summertime tallies in bat boxes, the citizen science campaigns to track bat flights by detecting their inaudible calls.
It’s a wide-scale effort that extends far beyond North Carolina — and even beyond the United States — and everyone involved is keeping their fingers crossed that white-nose will expose its kryptonite, that all this stone-turning will yield that one vital clue unearthing the fungus’ fatal flaw.
The hope? That someday, Cameron said, research will find an answer, and American bat populations will bounce back from their brush with death stronger than ever.
What is white-nose syndrome?
The fungus that causes white-nose syndrome, Pseudogymnoascus destructans, was new to science when it turned up in a cave in Schoharie County, New York, during the winter of 2006-07.
Since that debut, it spread rapidly across the eastern U.S. and Canada, spores most likely transmitted between bats and via cavers’ clothing and equipment. White-nose now reaches as far south as Mississippi, infecting 25 U.S. states and five Canadian provinces, arriving in North Carolina in 2011.
White-nose appears as a white fungus in hibernating bats, most commonly around their noses but also on the wings, ears or tail. Infected bats exhibit strange behaviors, such as flying outside during the day and clustering around the entrances to the caves and mines where they spend the winter, rather than moving further back. Current research indicates that white-nose changes how bats’ bodies function in ways that lead to a faster metabolism and reduction in fat reserves. Bats with white-nose have higher levels of carbon dioxide in their blood, which leads to dehydration, electrolyte loss and more waking up during the winter. Some infected bats will even leave the cave in search of food or water.
In Eastern North America, white-nose has killed more than 5.7 million bats, with 90 to 100 percent dying in some caves and mines. Scientists are working to pin down the dynamics of infection and transmission in hopes of finding a way to stem the tide of bat deaths.
Complete background information and updates about white-nose syndrome is online at www.whitenosesyndrome.org.
Dressing for the occasion
Dressing for a bat survey is something of a fine art. The rules are precise and the implications of improper attire significant.
As it turned out, I needed some schooling in the subject before following the pair of biologists I was meeting at Linville Caverns, near Marion, inside to count bats.
“I’ll tell you, it was hard to figure out this whole system the first time we did it,” said Sue Cameron, a wildlife biologist for the U.S. Fish and Wildlife Service. She apparently had it figured out now, seemingly needing just seconds to don her entire getup, featuring a white jumpsuit that made her look fit to tour an active radiation site.
“It took a lot longer, too,” she added.
Cameron and Katherine Caldwell, the N.C. Wildlife Resources Commission biologist partnering on the survey, were there for one of the nine cave surveys the Wildlife Commission conducted this winter to gauge how area bat populations were doing in the wake of white-nose syndrome, a disease caused by an invasive fungus that’s decimated bat populations across the Eastern seaboard. The fungus travels from cave to cave when its spores — tiny dots that are the fungal equivalent of seeds — hitchhike on the surface of an unsuspecting person, animal or piece of equipment.
That’s why scientists traveling between white-nose-positive and -negative caves must perform decontamination procedures — or “decon” — with a precision bordering on reverence. Everything that goes into the cave must be thrown away, treated with bleach or scrubbed down with Lysol and none of it can touch a person’s bare skin or base layers before disappearing into a plastic trash bag.
This includes notepads, cameras and voice recorders, so while Cameron and Caldwell suited up, I attempted to cover my camera and voice recorder with plastic wrap so that white-nose spores would stay out but the equipment would remain functional. As it happens, it’s pretty hard to take photos when the buttons, dials and lens body are smothered in plastic. And I hadn’t even put on my gloves yet.
The wrapping done, I traded out my reporter’s notebook for a clipboard equipped with waterproof paper that could be wiped down when we left the cave. I caught the pair of gray sweatpants Caldwell tossed me to pull over my jeans and zipped up the Tyvek suit, size medium, she gave me next.
“What we usually do is wear one of the medium Tyveks on the bottom and a large on top of that,” she explained.
But even with rubber boots and two separate Tyvek suits, I still wasn’t ready to enter the cave.
“I’m going to put a piece of duct tape on that interior zipper because sometimes they can come down,” Cameron said, bringing over a roll. “And the hood, see how it’s annoying and you can’t see? We usually do a little tape dab on top so it keeps it off our eyes.”
Feeling like some kind of HAZMAT-edition Barbie, I stood still while the two biologists finished me up. They wrapped the junction between my boots and interior suit with duct tape, handed me a pair of thick orange rubber gloves and taped my sleeves to them. I took a plastic helmet with built-in headlamp and ditched the string bag I’d brought along — anything fabric I carried outside my suit would have to be immersed in bleach water before seeing the light of day again.
There was just one thing left to do before entering the cave: take the requisite look-at-me-wearing-a-hazard-suit photo. When else would I find myself dressed up like a cross between a beekeeper and nuclear disaster responder?
But at this point, the three of us were covered head-to-toe in rubber and Tyvek, and iPhones don’t respond to plastic fingers. Caldwell, a veteran of frigid Indiana winters, solved the problem — she took the picture with her nose.
— By Holly Kays