In heavy woods, and under the cloak of night, trying to catch bats in their element might seem like a fool's errand. Yet the effort might just provide answers that help save some of a threatened Minnesota species from certain death.
That underlying motivation surfaced when wildlife researchers from the state Department of Natural Resources and the University of Minnesota Duluth gathered deep in some hardwood stands in East Bethel, Minn., on a night in early July. With thunderstorms threatening, teams of bat chasers set off along service roads. At three locations, they raised a combination of ultrafine mesh nets 25 feet in the air, anticipating bats on the move as the light drained from the woods.
They hoped most to capture — and then track — the northern long-eared bat, one of seven species in the state, and the one under the most duress. A deadly fungal disease called white-nose syndrome has killed millions of bats in the eastern United States and eastern Canada. Minnesota species have been victimized, too.
Researchers are halfway into a three-year study. They're hoping to learn more about the northern long-eared's summer routine, and what kinds of trees it uses to raise its young in the summer. Identifying those trees and protecting that habitat might be the best chance at saving some of the species — and others — as the fungus becomes more lethal here. And it will, most observers agree.
"What we hear is people say, 'We want data from Minnesota,' " said Rich Baker. "We want to figure it out in Minnesota."
Baker has a keen interest as endangered species coordinator for the Minnesota DNR, and it's hoped that spending several days buried in the woods of Cedar Creek Ecosystem Science Reserve in East Bethel might provide some clues.
The Cedar Creek reserve sits on the northern edge of the metro area. The site was a new location — and the southernmost — for netting and tracking in Minnesota thus far. Owned by the University of Minnesota, the 5,000-acre Cedar Creek was something of an ideal, controlled setting. And yet for researchers, catching bats, attaching minute radio transmitters and then tracking their whereabouts and roosts is delicate and challenging work.
It's bats' indoor habitat where the trouble is centered. The northern long-eared bat is one of four Minnesota species that hibernates in caves, making them susceptible to the white-nose fungus that has been wreaking havoc in their ranks. The disease is named for the white powdery substance that appears on the face and wings of infected bats. It has reportedly killed as many as 6 million of the creatures across North America and, judging from counts at known hibernation sites, the U.S. Fish and Wildlife Service estimates that the disease has killed up to 99 percent of the northern long-eared population in the northeastern United States. It was first documented in a cave in 2006 in New York state.
In Minnesota, the northern long-eared is listed as a species of special concern along with three others — the little brown, big brown and tricolored — that winter in caves and mines. The USFWS put the northern long-eared on its federally threatened list in April 2015. In Minnesota, hundreds of bats were found dead in the cold near the main entrance of the mine at Lake Vermilion-Soudan Underground Mine State Park last January. State officials expected the discovery, as the infectious disease has spread. The disease surfaced in Minnesota in 2013 at the Soudan mine and at Forestville/Mystery Cave State Park in southeastern Minnesota.
Scientists say infected bats act abnormally, moving toward the mouths of their hibernation sites, or hibernaculum, and sometimes making daytime flights during winter. In doing so, the bats burn through their fat stores and starve to death.
"Unfortunately, we expect that those numbers are going to increase over the next winter or two," said Jill Utrup, a USFWS biologist in the Twin Cities.
Why does the northern long-eared appear to be most susceptible to the disease? There are some clues, said Utrup, who gets regular updates from the Minnesota researchers.
Utrup said the bats are typically found in their hibernaculum in the areas with the highest humidity, "where the fungus really thrives."
"Also, they are one of the first bats to enter the hibernaculum and one of the last to leave. So they are exposed a lot longer, as well," she added. "Those are challenging things."
A real threat
White-nose syndrome is clearly a disease on the move, having surfaced for the first time in the western United States in March when a case was confirmed in a little brown bat in Washington state. The most recent discovery of an infected bat — a tricolored — occurred in Rhode Island for the first time in June. The disease now has been reported in 29 states and several Canadian provinces.
On the front edge of the threat, Minnesota researchers find themselves with an urgency to their work, trying to zero in on the threatened bat's summer roost sites. They want a clearer picture of where bats live during a key period of the species' life cycle: the females' maternity phase in June and July. The National Guard has netted at Camp Ripley and the U.S. Forest Service is involved, too, as researchers work their way across the state. More netting in different parts of Minnesota is planned next summer.
"The typical pattern is that it takes about two years to really see the effects on the bat populations" once white-nose syndrome is confirmed, said researcher Ron Moen of the Natural Resources Research Institute at UMD. So the study continues with a burgeoning health crisis as backdrop.
That is both positive and troubling news, Baker said.
"It's fortunate, or more accurately, unfortunate that we have happened to have started the project before white-nose got here," said Baker, "and we're going to run it during the infection, during the plague.
"We didn't know. Now, we are seeing the wing damage from exposure to white-nose syndrome. We saw very little last year, but we're seeing more this year."
The results of the research in Minnesota, which is expected to continue into 2018, will have environmental and economic implications. Bats play an important part in the Minnesota ecosystem as voracious insect-eaters, and provide an estimated $3.7 billion in pest management and pollination to U.S. agriculture, according to the DNR. The results of the study and the bat's ominous federal status have implications for timber-harvesters. Defining the northern long-eared's summer habitat, in particular, could lay the groundwork for forest management that helps safeguard young bats facing a deadly threat in their hibernacula, Baker said, adding "how do we make sure there are roost trees for bats in the future?"
Judging from preliminary findings after netting elsewhere earlier this summer, the bats showed a preference for aspen in the north and oaks at Camp Ripley, Moen said. But more so, the early signs are that the bats are flexible when it comes to choosing trees and their cavities and crevices to settle in.
Field work
Back at Cedar Creek, researchers netted two female northern long-eared bats among four total over the course of several hours. What with the turbulent weather and the successful netting the previous night (five female northern long-eareds), it was considered a good night's work. Headlamps illuminated a screen house where NRRI staff huddled and took meticulous notes, from reproductive phase to wing size, of their captives. They checked, too, for signs of white-nose: pinholes or a mottling of the skin on the fine membranes of the wings. (It appeared on one of the northern long-eared bats that was fitted with a transmitter and lit out into the night.)
The team was sensitive to its unsettled subjects, which squirmed and chirped in protest. Staff trimmed back hair and adhered transmitters to the bats for the bookend of the research: Tracking them to their destination trees the next day. Both went to dead oaks. Researchers set up camp just before sunset the next night to watch the oaks for bats; 49 bats emerged from one, including the bat with a transmitter. The surveys can be inexact work, challenged by the night weather, the tree's surroundings and, of course, the bats' intentions. Most tend to travel within 300 to 400 meters of where they were netted. Still, there are takeaways, Baker said.
"We're getting results as we go," he said. "We didn't know if there was a preference for a size [of tree], age, species, stand type. We haven't finished the analysis. We don't know yet.
"But there are indicators. We see that there is a tendency to use what's available, to be opportunistic by the bats. I think that is a very important finding and really interesting," Baker said.
For example, researchers are beginning to piece together how far a bat might travel between roost trees on successive nights, how far they travel from forage sites to roost sites. "All of that is going to be important," Baker said.
In general, researchers can pick up a signal from a bat within a half-mile, but most times it's about a quarter mile, Moen said. Success depends on where the bats are, too. If they are buried in a deep cavity of a tree, it can be a challenge to stay connected to them. And there is a time factor. The teams are on a tight window with their subjects, Moen said. The transmitters either lose battery life or are groomed off by bats, giving researchers about six days or so to track their mercurial subjects.
For Morgan Swingen, the NRRI's field coordinator on the dark and stormy night at Cedar Creek, it is work in uncultivated terrain, literally and figuratively.
"Northern long-eared bats really haven't been studied very much in the Midwest at all, and a lot of the information we have about what types of roosts they use are from other areas of the eastern U.S.," she said. "We're just trying to gather basic data on these trees and see if they are using specific trees we can try and protect more in the future. Or if it seems they are more general or using what is available, that could be a good thing and mean that roosts won't be limited. We just don't have enough information to say either way."
Bob Timmons • 612-673-7899
