Giorgia Auteri is still haunted by what she saw in an abandoned mine in 2014. As a graduate student studying how bats hibernate, she had frequently climbed into mines and caves to observe thousands of sleeping bats hanging from the walls.
But when she walked into the mine in Michigan’s Upper Peninsula in 2014, she discovered heaps of dead bats on the floor.
“It smelled of death,” recalled Dr. Auteri, now a biologist at Missouri State University.
A fungus began spreading among bats in North America in 2007, causing a disease called white-nose syndrome, which marks the animals with patches of pale fuzz before killing them. The pathogen first appeared in New York State and then spread west. Since Dr. Auteri’s grisly discovery, it has moved even farther west, killing many millions of bats all the way to the Pacific.
White-nose syndrome is not only devastating bats, but also the ecosystems in which they live. While many people have traditionally looked at bats as rabies-carrying pests, they eat vast numbers of bugs. Without them, insect populations can explode. This month, researchers reported that the decimation of the bat population from white-nose syndrome has led farmers to use extra insecticides against crop-eating insects — an increase they linked to a rise in human infant mortality.
Back in 2014, Dr. Auteri brought some of the dead bats from the Michigan cave to her lab to study. She said it felt like a form of grieving, of bearing witness to a catastrophe that seemed unstoppable.
But a decade later, her grief has turned into hope. Dr. Auteri and other researchers have made some crucial insights about how white-nose syndrome kills bats, and that knowledge has inspired a campaign to stop the mass death. Now, scientists are attacking the fungus and finding ways to help bats survive infections.
“I really feel like we’re starting to see some signs of recovery finally,” said Greg Turner, a wildlife biologist at the Pennsylvania Game Commission. “I feel much more comfortable than I used to feel, that’s for sure.”
Stopping the Attack
The fungus, Pseudogymnoascus destructans, is native to Europe. It doesn’t harm bats there because their immune systems keep it in check. It’s unclear how the fungus reached the United States; a traveler may have carried a spore of it on a shoe to North America, where bats lack immunity and have proved to be dangerously vulnerable.
Once infected, bats carry the fungus with them as they fly to shelters for hibernation during the winter — areas that biologists call hibernacula. When the fungus arrives in a pristine hibernaculum, its spores can lurk for years.
In 2013, researchers at the University of Illinois discovered that a chemical called polyethylene glycol 8000, commonly used in human medical applications, can coat the spores and keep the fungus from growing.
That discovery got Mr. Turner and his colleagues thinking: Could the chemical stop the fungus from infecting hibernating bats?
In the summers of 2018 and 2019, the researchers entered an abandoned train tunnel favored by bats in wintertime and sprayed the walls with polyethylene glycol 8000. “It coats all of the spores that are in the site waiting for the bats to return,” Mr. Turner said.
The spraying led to a drastic drop in white-nose syndrome in bats that hibernated in the tunnel, Mr. Turner and his colleagues reported last year. Now the researchers are spraying eight other sites and comparing them with 30 untreated hibernacula to see if the chemical consistently helps the bats.
“Every day we can delay the initial infection increases the chances that bats will survive to the end of winter,” said Brent Sewall, a biologist at Temple University who is on the research team.
Home Improvements
Mr. Turner and his colleagues are also trying the help the bats by redesigning their living quarters.
The idea emerged from an unexpected observation early in the white-nose syndrome pandemic. Once white-nose syndrome hit a mine or a cave, some of the bats would start hibernating in different parts of the hibernaculum. “Our survivors were selecting roosts that were cooler,” Mr. Turner said.
Further research revealed why sick bats made the move. To fight fungal infections, bats have to use up precious energy and water, which often rouses them from their torpor. The sick bats fly around their hibernaculum, burning even more calories as they search for water to drink. Many die by the time spring arrives.
But by moving to a colder spot in a hibernaculum, bats can improve their odds of survival. The lower temperature slows the growth of the fungus and helps bats plunge into a deeper hibernation, from which they are less likely to rouse.
This finding prompted Mr. Turner and his colleagues to make caves and mines cooler. They engineered passageways into the shelters, some to let in cold air and others to let warm air flow out. Once they lowered the temperature a few degrees, the researchers witnessed a big increase in the number of bats surviving the winter.
This fall, Mr. Turner and his colleagues are starting an even more ambitious project: building an artificial hibernaculum.
A construction crew will build a set of concrete chambers and tubes into a Pennsylvania hillside, with openings designed to take in cold air and a pool of water at the bottom to stabilize the temperature. Once the hibernaculum is assembled, the crew will cover the structure with earth.
“The idea is to make pretty much exactly what they’re looking for in the wild and see if we can draw survivors into that site,” Mr. Turner said. In the summers, biologists will spray polyethylene glycol 8000 or a similar compound to keep any spores that get into the hibernaculum in check.
If the first hibernaculum supports a healthy bat population within two or three years, Mr. Turner hopes to build more across the state.
“With any proof of concept, you have to demonstrate it works,” Mr. Turner said. “But I’m expecting a lot of success out of it because it’s the next evolution of what we’ve been doing.”
Summer Buffet
When bats emerge from hibernation, they fly for miles each night to catch insects. They are in a rush to build up enough fat to get them through the next winter. “They’re at the knife’s edge,” Dr. O’Mara said.
This means the fight against white-nose syndrome is a year-round battle. This past spring, Teague O’Mara, an ecologist with Bat Conservation International, and his colleagues created a feast for bats in Southern Illinois, hoping to fatten them up over the summer in case they needed the extra energy to fend off the fungus in winter.
The researchers are trying to provide more food for them on the strips of land cleared by utilities for their power lines. Dr. O’Mara and his colleagues arranged for native flowers and grasses to be planted on some experimental plots, which bloomed by summer. “They look like our native prairie,” Dr. O’Mara said.
Dr. O’Mara expects that the native plants will provide a feast for insects, which will in turn become a feast for bats. If preliminary studies like this one succeed, he hopes that power companies will allow more of their plots to be made into bat-fattening corridors.
To judge how the experiment is going, Dr. O’Mara and his colleagues are eavesdropping on the echolocation calls bats use to track their prey. “We’re seeing a lot more activity,” he said. “What that means, we don’t really know yet. But at least they’re drawing bats in.”
Protecting Mother Bats
Female bats don’t just hunt insects over the summer. After flying through the night in search of food, they return by the hundreds to maternal colonies, where they nurse their pups.
They sometimes congregate in a house or barn. Unfortunately, people have often responded by poisoning the animals. Even before white-nose syndrome arose, these killings nearly wiped out some species of bats. When the fungus arrived, an end to the carnage became all the more urgent.
Wildlife biologists have been developing methods to get bats out of buildings, such as by installing one-way doors so that the bats can leave the colonies in the fall but not return the next spring.
Alyssa Bennett, a small mammal biologist at the Vermont Fish and Wildlife Department, said that the public has become more eager to help move bats out of buildings safely. They have also been putting up birdhouse-like bat boxes designed to attract female bats searching for a place to rear their pups.
This new attitude has made Ms. Bennett optimistic that more pups will survive each summer and that bat populations would rebound. “The hope is about people,” she said.
Exit Strategy
After Dr. Auteri got over the shock of seeing the dead bats in the Michigan mine, her inner scientist took over. She set out to compare the bats that died of white-nose syndrome with the few that survived.
She sequenced DNA from 29 little brown bats that perished across northern Michigan in 2014. Then, in 2016, she got blood from nine bats that were old enough to have survived the initial outbreak of white-nose syndrome in the region.
She found a striking contrast. “The survivors are genetically different in some regards,” Dr. Auteri said.
The genes that differed are involved in putting on fat and waking up from sleep — two traits crucial to a successful hibernation. Dr. Auteri suspects that the surviving bats had mutations that made them more likely to withstand the fungus.
“If they’re heavier, then they can better survive the more frequent arousals,” Dr. Auteri speculated. “And if they’re not as prone to waking up, then they can also avoid extra fat loss.”
Dr. Auteri believes that if these genes can be successfully passed down through generations, the bats will build their populations back up. For now, however, conservation biologists are going to have to take drastic measures to preserve the bats. “But we won’t necessarily have to do that forever,” she said.
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