Hidden away in the woods near the upstate New York town of Lake George is a cave. The entrance of the cavern, an abandoned graphite mine, is almost perfectly round, with a trickle of water running out of it. On a weekday morning in late February, researchers, led by Carl Herzog, a wildlife biologist for the New York State Department of Environmental Conservation, gather at the cave mouth and swap hiking boots for waders before filing in.
Kate Ritzko, a fish and wildlife technician for the Department, reminds everyone of proper caving etiquette: Make sure geotagging on phones is turned off, so that no one accidentally reveals the location of this sensitive site; and keep voices low, so as not to disturb the bats the team is here to count.
Inside the cave, the swishing sounds of waders bounce off the low, angled ceiling, mixing with the trickle of water and the occasional fracture of ice as someone’s foot punctures the stream’s frozen surface. Icicles rise from the ground like impermanent stalagmites. But as we move deeper into the cave, the ice disappears. That’s largely why bats seek out these caves in winter: The surrounding earth, like a blanket of soil and stone, insulates the interior from the frigid temperatures outside.
We spot the first bat, tucked into a corner, upside down. It appears healthy enough. Oblivious to our presence and our bright headlamps, this is a big brown bat (Eptesicus fuscus), and it’s one of the species resistant to the fungus that has killed millions of bats throughout the eastern United States since it first emerged in 2006.
The fungus is why we’ve come to this cave. It grows on hibernating bats, spreading across their face, wings, and any other furless skin. Infected bats typically develop a distinctive white semi-circle of fungal growth around the nose, which is the source of the deadly disease’s rather innocuous name: white-nose syndrome. Even before the fungus appeared, Herzog and others at the state agency had been conducting surveys in caves to get a handle on bat numbers—of both common species and endangered ones. Across the country, state and federal environmental departments have long done the same thing, generally visiting caves every other year to minimize disturbance. But in the era of white-nose syndrome, these surveys have provided grim tallies of the utter devastation the fungus leaves in its wake.
In some large bat colonies, more than 90 percent of bats have been wiped out since the fungus first appeared; in many smaller colonies, every individual died. While the fungus has been a threat to the very existence of some endangered bat species, it’s the ecological ramifications of losing millions of once-common bats that worry scientists most. This cave, for example, used to be filled with a different type of bat, one that until white-nose arrived was the most common bat species in the northeast: the little brown bat (Myotis lucifugus). Today, we’ll find only two of them in a cave that used to house more than a thousand. The species is now listed as endangered in Vermont; millions have perished across the animal’s range.
Just a few miles west, though, is a larger abandoned mine that has offered a rare bright spot in the white-nose saga. In 2000, a survey counted about 184,000 little brown bats there. Then white-nose swept through. In 2010, surveyors counted only about 2,000 of the bats. (Since the population had probably grown to close to 200,000 in the years leading up to the crisis, Herzog says, what remained represented only about 1 percent of the original number.) But then in 2014, something strange happened. The population seemed to stabilize. It was still a tiny fraction of its original size, but at least the numbers hadn’t hit zero, as they had elsewhere. And last year, another surprise: The population had more than doubled since 2010, up to a new, post-white-nose high of about 4,500. Bat scientists hope this is a beacon.
Deep in a cave, if you turn off your headlamp, the blackness is utter. Your eyes, unprepared for a total lack of stimuli, will sometimes tell your brain that they see something, that there is light in the darkness.
So it may be with bat scientists, who are straining to see even the slightest glimmer of hope, any sign that the vanished bats may stage a comeback. And while some of those gleams in the dark may just be illusions, others may be true spots of light. This cave, it seems, is one such glint.
There are others, too. In at least four other locations in New York, little brown bat colonies have either stabilized after crashing or have started to climb back up. Kate Langwig, a professor of biology at Virginia Tech, notes that even if you lose 85 percent of a bat colony, if you started with 100,000 bats, you’ve still got 15,000 left. “Fifteen thousand bats is a lot of bats!” she says.
In a recent paper about such persistent populations, Langwig compared the New York populations with those in states where bats haven’t bounced back, including Virginia and Wisconsin. She and colleagues found that the amount of fungus on individual bats in New York caves seemed to level off once the pathogen had been in the area for a few years, whereas in the non-resilient populations, it continued to climb. “In New York, bats appear to actually be resisting fungal infections,” says Langwig. “It suggests that they could continue to grow, that this is a trait that they could potentially pass on to their young, and that would enable them to survive long-term.”
There are a few possible explanations for this, Langwig says. It could be that surviving bats are choosing roost areas that are slightly colder and dryer—less ideal for the fungus. Or, bats could be evolving some sort of resistance: Perhaps surviving bats have skin microbiomes that keep the fungus in check. It’s also possible, she says, that surviving bats have an immune response that becomes active later in the winter season than their fallen brethren. One way scientists think white-nose kills bats is by causing them to wake from hibernation more frequently. Bats that stick to their usual cycle of torpor and occasional arousal throughout the winter would likely be better able to preserve their energy stores long enough to make it through to spring.
Although much remains uncertain, Langwig and others hope that figuring out what’s special about some of New York’s bats may provide clues about how to protect colonies elsewhere.
While all biodiversity losses affect ecosystems, the disappearance of bats has broader ramifications than most. When any abundant species suddenly begins to disappear, the dramatic loss can throw food webs and other networks out of balance more so than the loss of rare or endangered species. Bats, with their voracious appetites and highly efficient hunting techniques, not only protect us from disease-causing organisms like mosquitos, they also save the American agricultural industry about $25 billion per year, and maybe as much as twice that, by eating the insects that feast on crops.
All that serves as motivation for Langwig and the other scientists, federal officials, and conservationists who have been working to solve the mystery of white-nose syndrome ever since a routine cave survey first brought it to their attention.
A Growing Epidemic
Since it was first detected in February 2006, white-nose syndrome (WNS) has spread across much of eastern Noth America and is now making its way west. This map indicates counties and districts in which WNS or the fungus Pseudogymnoascus destructans has been detected at known bat hibernation sites. (Last updated June 1, 2018).
Data provided by the White-nose Syndrome Response Team at www.whitenosesyndrome.org.
Jeremy Coleman was also at the 2008 meeting; he has been the Fish and Wildlife Service’s national coordinator for white-nose syndrome since that year. “It became apparent that this was something bigger than we’d ever dealt with before,” he remembers. The 2008 meeting kicked off a period of frenzied work that Coleman helped to oversee as he raced to develop connections among the Service, state agencies, non-profits, and university scientists.
But white-nose was already several steps ahead. By the time of the next meeting, in 2009, cases had been confirmed in nine states, spreading as far south as Virginia. “There was a feeling that it was going to take some time for it to spread, and that we had some time to deal with it,” says Coleman. Even the wildlife managers from West Virginia, Virginia, and Tennessee who had gotten involved early were caught off guard by the speed and fury with which white-nose swept southward, causing massive die-offs like those in the north.
By 2009, Blehert and his colleagues had given the fungus, which by then had killed more than a million bats, a name: Geomyces destructans. The fungus has since been reclassified into a different genus (Pseudogymnoascus), but it has kept its apt species name: destructans, the destroyer.
In 2011, scientists confirmed what many already suspected: The fungus was indeed causing the die-offs, not simply a symptom of some other disease. But a troubling question persisted, one that scientists are only now beginning to answer. It wasn’t clear, exactly, how the fungus killed bats. The fungus itself didn’t seem to cause much in the way of tissue damage, beyond some scarring, and it didn’t produce any toxins that scientists could detect. One important clue, though, was that it seemed to only kill bats while they were hibernating.
When bats enter a state of torpor, they undergo dramatic physiological changes. A bat’s heart and breathing rates drop, as does its body temperature; some can go for more than two hours without taking a single breath. They’re about as close to death as a mammal that’s not actually dying can be. Periodically, though, they’ll wake up, although it’s not exactly clear why, says Thomas Tomasi, who studies bat energetics at Missouri State University.
Whatever the reason, in that brief period of arousal, when a bat’s heart rate, metabolism, and temperature rise to something closer to normal, it can use as much energy in an hour or two as it uses in a few weeks of torpor. And that’s where white-nose strikes, Tomasi and others have come to suspect. Bats infected with the fungus wake up far more frequently than uninfected individuals do. And their small bodies—just 10 grams in the case of little brown bats—carry very little in the way of extra energy reserves. As a result, bats that use up their winter stores before spring either starve to death or leave their caves early in what becomes a vain search for food in the unwelcoming, bug-less cold.
That raises another question: Why is it that some bat species, like the big brown bats we found in the New York cave, or those closely related to susceptible species, like the eastern small-footed bat (Myotis leibii) have relatively high survival rates even after becoming infected with white-nose? It could be, says Tomasi, that those bats—and their immune systems—simply ignore the fungus. “Their immune system is trying to do less,” he says. “It’s not that their immune systems protect them—their immune systems are just ignoring it, and not causing the animals to raise their metabolism.”
This may explain why Langwig’s bats are surviving and slowly beginning to recover. Those bats may be the ones with less-responsive immune systems, and therefore the ones that wake up less and have better odds of surviving through the winter.
Earlier this year, scientists published a paper comparing Pseudogymnoascus destructans to its non-pathogenic close relatives. And they noticed a weakness. The Destroyer, it seems, is particularly sensitive to sunlight.
Specifically, white-nose fungus seems to be missing a number of genes associated with repairing damage to its DNA caused by ultraviolet light. As any user of sunscreen knows, UV light can damage cells, causing mutations in the DNA—generally bad news for an organism. So most plants and animals have some genetic mechanism to repair that damage. But according to recent research, white-nose fungus likely co-evolved with bats in Europe and Asia for millions of years—which means it’s been hanging out in dark caves for so long that it may have lost its ability to repair damage from the sun. This long co-evolution may also explain why bats in Europe and Asia are frequently found with white-nose fungus on their bodies, but don’t succumb to the disease. Susceptible bats may simply have died off long ago.
Finding a weakness like UV light is one thing. Exploiting it is quite another. “The tendency is just to say, ‘Hooray, we found the Achilles’ heel!’” says Jonah Evans, a mammalogist for Texas Parks and Wildlife. “And I’d be super excited if we do—but I also think there are major logistical problems that need to be solved first,” he says. One bat researcher suggested a contraption at the entrance to caves that is triggered when bats fly through it, dosing them with UV light to knock back any fungus that’s growing on them.
One of the difficulties of trying to eradicate white-nose fungus from a cave is that caves tend to harbor unique organisms: blind, pigmentless crustaceans, fish, amphibians, insects, bacteria—and other fungi. So while dousing a cave with a fungicide or UV light might indeed protect the bats living there, it could also harm native species, thereby disrupting the ecosystem and potentially causing further harm.
Maarten Vonhof, a biology professor at Western Michigan University, has been working on one possible solution, though. He and his colleagues have been testing a molecule called chitosan, derived from chitin, a material found in the exoskeletons of insects and other arthropods. Chitosan is known to have antimicrobial properties and to help wounds in humans heal more quickly. When the scientists tested chitosan directly on white-nose fungus in the lab, it not only slowed its growth, it also killed its spores. And, crucially, chitosan only harmed native cave fungi when applied in much higher concentrations than required to treat white-nose fungus.
When white-nose infected bats in the lab were treated with chitosan, Vonhof found higher rates of survival and less fungus on the noses of treated bats. Encouraged, he and his colleagues moved on to field trials, to see whether chitosan treatments could help wild bats as well. A pilot study in Wisconsin lent further support: The survival rate of chitosan-treated bats was double that of untreated bats.
A larger study two winters ago in Illinois and Michigan, however, gave more equivocal results. Chitosan treatment seemed to reduce the amount of visible fungus growing on the skin of infected bats, as well as tissue damage caused by the fungus—but it didn’t appear to improve survival rates. But, Vonhof noted, that winter was especially short and warm, allowing bats to feed later into the fall and start feeding again earlier in the spring, which could explain the lack of difference between treated and untreated bats, as well as the high survival rate overall.
This past winter, Vonhof and others conducted another set of field trials, these in Texas and Michigan. Those results aren’t yet available, but Vonhof hopes they will reveal chitosan’s potential role in the fight against white-nose.
A vaccine for white-nose fungus is another possible solution. The same team that helped to save black-footed ferrets from extinction by developing a vaccine for sylvatic plague is working on this now, but that work is still in its early phases.
One of the biggest challenges for all of the most promising treatments is that, by and large, they require direct application on individual bats. And, considering the millions and millions of bats still out there, that’s simply not practical on the scale of an entire continent. For endangered species, where the remaining numbers are already low, this approach might make sense, especially in the cases where infected bats are being rehabilitated in captivity. But for the rest of the bats out there? “We move ahead with our work on treatments, because of course we want to find treatments,” says Vonhof. “But looming over that, for all of us, whether it be UV, or chitosan, or a vaccine, if they can come up with one, is, how do we get that out to very cryptic animals that are night-active, that we don’t know a lot about?”
The leading edge of the white-nose wildfire now stretches from northern Texas up through Oklahoma, eastern Wyoming, and into Manitoba in Canada. In 2016, infected bats showed up in Washington State as well, though it’s not clear how the infection jumped across the country. In general, the front has moved in a steady progression outward from its epicenter in New York State. Interestingly, though, bats don’t typically die as soon as white-nose shows up; instead, almost without fail, after white-nose is detected in a cave—say, from samples taken from the cave walls or floors—bats begin dying two years later.
At a cave in eastern Oklahoma, white-nose was first detected two winters ago. And within just a few feet of the entrance, on a sunny afternoon this March, Richard Stark finds the small, desiccated body of a tricolored bat (Perimyotis subflavus), still clinging to the cave’s limestone wall.
“I was afraid of this,” says Stark, a biologist with the Fish and Wildlife Service, as he pulls the bat off the wall, its claws still latched onto the stone. The two previous nights, he and a team of fellow biologists had set up nets at the cave’s entrance to catch bats leaving. Their numbers, though, had been abnormally low. Today, he’d been hoping that lots of the bats were simply still in the cave, and hadn’t been active because of the low temperatures. That could still be the case. “Hopefully that’s the only dead bat we find,” he says, sealing the bat in a Ziploc bag to be overnighted to the U.S. Geological Survey’s National Wildlife Health Center in Wisconsin for testing. But his tone isn’t optimistic.
Indeed, just a bit deeper into the cave, where the sunlight disappears, we find another dead bat, this one also still attached to the rock. Stark bags it and leaves it on a ledge to be picked up on his way out.
To get to the main chamber where most of this section of the cave’s bats reside, we have to crawl. This is no hands-and-knees crawl; this is a push-your-bag-in-front-of-you, on-your-stomach crawl. The entrance is less than two feet high. Stark goes first, easily outpacing me, but waits for me at any points along the tortuous route where I might take a wrong turn. Near the end, maybe five minutes later, Stark cautions me to keep my voice down. We’re about to enter the “anteroom,” not the main, large cavern, but a spot where gray bats—one of this region’s endangered species—are known to congregate. And congregate they do, forming two pulsating, squirming masses on the ceiling, a few dozen gangly, bony wings and gray-brown fur. Here and there, glints of silver metal reflect our headlamps: tags, affixed by Stark or his colleagues to track the population’s movements and numbers.
The second crawl is even longer and narrower than the first. As Stark moves out of sight, I can hear his movements reverberating through the rock around me, and I’m acutely aware of the weight of the earth just inches above my helmeted head.
Finally, I emerge into the larger space, and can stand again. The room is long, with a fracture running the length of it on the ceiling. Water dripping through that crack for millennia has carved out the standing space in this large cavern.
I see Stark sitting on a ledge of rock, staring up at the ceiling. Something in his posture looks defeated. “This is a very symptomatic bat right here,” he says. As soon as I sweep my headlamp across where he’s looking, I see it: a flash of white. Approaching, I can see the fungus clearly on the animal’s muzzle. There’s no longer any question: White-nose is killing bats here, too.
Stark goes to check the rest of the cavern as I stay behind to catch my breath. When he returns, he’s only found seven bats. “This is nothing like normal,” he says.
Once he’s finished counting the bats in that room, we start to make our way back out of the cave—crawling back through the tight tunnels, through the anteroom with the clustered gray bats, and finally back through the metal gate. Outside, Stark strips down to his underwear. Everything he wore in the cave—boots, jumpsuit, helmet, light—goes into plastic bags for decontamination later on. The last thing he wants to do is carry the fungus to another cave.
As we drive away from the site, Stark is clearly discouraged. “I’ve been going inside this cave for a long time,” he says. “It’s like it seems sick, in a way.”
Stark and the other researchers, wildlife officials, and conservationists who have been trying to save bats for the past decade are regularly frustrated by this fight. To have so vast a crisis and be unable to do much but watch it unfold is maddening. There are those who think letting the fungus run its course, and simply seeing who survives at the other end, is the best, or only, course of action. Langwig’s work on the bats that are persisting suggests that such an approach is not a capitulation. “I think we’ll have little brown bats in New York. I feel very strongly about that,” says Langwig. “And Vermont seems to be seeing similar results.” She’s less optimistic, though, about other states, like Virginia and Wisconsin.
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From the tiny spaces of an urban yard to the remote corners of Earth, Michael Durham has often sought out opportunities to document subjects that are beyond human perception. Among other endeavors, he has crawled into caves crowded with bats, designed and deployed remote cameras to photograph wild cougars, and studied the flight of African wasps. The more elusive the subject, the more interesting he finds it to be. Durham brings years of experience as a commercial photographer to his work as a wildlife photographer, combining subject, light, and moment to make powerful images that capture an idea or emotion.