Bat study hones-in on nesting trees
ST. LOUIS COUNTY, Minn. -- She was hissing and squealing and trying to open her tiny mouth wide enough to nip the glove of the biologist who was holding her.
But the young female northern long-eared bat -- now wearing pink band No. L-A-1171 -- wasn't much of a match for U.S. Forest Service researchers. After all, she weighed less than half an ounce.
L-A-1171 was delicately weighed, measured, banded and examined for any health problems.
"Isn't she cute? She's being so cute for us,'' said Kari Kirschbaum, a wildlife biologist from the Chippewa National Forest.
The bat seemed fine -- the experts saw no sign of the deadly white-nose syndrome fungus -- and was quickly sent on her way to chase mosquitoes for the rest of the night.
Had she been an older female, she would also have been fitted with a tiny VHF radio transmitter so crews could track her and see where she hung out -- literally -- during the day.
It's not exactly clear to scientists what trees northern long-eared bats roost in during the day or what trees females raise their single pup in June and July. And with northern long-ears newly protected by the federal Endangered Species Act, scientists are scrambling to fill in the blanks on the bat's life cycle.
Bats eat lots of bugs. They winter in caves. They fly at night. Beyond that?
"It's amazing how much we don't know about them,'' said Ron Moen, biologist for the Natural Resources Research Institute at the University of Minnesota Duluth, who is helping coordinate the effort.
The U.S. Forest Service, NRRI, Minnesota Department of Natural Resources and other agencies are working together as part of an ongoing forest bat research project across Minnesota.
The Forest Service began the effort in 2013. But it gained increased importance in April when the northern long-eared bat was given "threatened'' status by the U.S. Fish and Wildlife Service. This year the state's Legislative and Citizens Commission on Minnesota Resources, which spends the state's lottery profits, added $1.25 million to keep the project going into 2018.
So far this summer 16 northern long-eared females have been fitted with the transmitters which are attached to their backs with surgical glue. The units are supposed to last for 21 days, but the bats usually shed them -- they are prolific groomers of each other -- after just a few days.
Every night is different
Along a two-rut forest road about 50 miles straight north of Duluth, Forest Service researchers with headlamps waited for sunset and dusk. By 9:30, their high-frequency bat detector started crackling like popcorn popping, signaling that it was time to go to work.
The crews capture bats in fine-mesh nets strung 25 feet high in the woods, usually placed in small openings or across forest roads. Nets are checked every 15 minutes and captured bats are gently removed from the nets and quickly moved to a nearby screen tent to be poked and prodded. A really good night will fetch up to 19 bats caught and recorded. Most nights, like this night last week, it's five or six.
If there's mist on the nets, or if they flutter in the wind, bats seem able to avoid being caught -- their echolocation systems apparently detect the trap.
The research crews catch most kinds of native bats -- reds, little browns, big browns, hoary and northern long-eared -- and they keep track of what they catch as part of a national clearinghouse of bat research.
But their primary goal is to determine habitat needs for the northern long-eared bat to help wildlife managers, federal regulators and Minnesota's timber industry decide how to preserve bats, and bat-roosting trees, while still allowing logging across the region.
Northern long-eared bats spend their winters in caves and summers in trees. It was hypothesized they might like a specific type of tree, making it easy to decide what trees to leave standing in the woods.
Three years into the effort, however, "it turns out they are generalists. They are opportunistic. They will use just about any tree that has a crack or crevice in it,'' said Rich Baker, endangered species coordinator for the Minnesota DNR. "Anything with sloughing bark or holes is a candidate."
Maples are popular, but so are aspen where they are prevalent (just about everywhere), and oak trees are favorites, too. Nearly all of the confirmed roost trees have been larger than 6 inches in diameter. Most are hardwoods.
"If it turns out like it's looking now, that they like a broad spectrum of trees, that's not necessarily bad either. Maybe it means we just work to have a diverse forest in as many places as possible; a good mix across the landscape. That's often what is best for a lot of species'' of wildlife, Baker said.
The more bats they find and follow, the more variety researchers find in tree roosts. But there's also been some new information on the bats' reproductive process.
"We think we're learning some interesting things about timing (of bat pregnancies) too. We have found some that are already nursing and some that are still pregnant, so it's not happening at once,'' said Tim Catton, the lead bat project biologist for the Superior National Forest.
Earlier in the evening we traced one northern long-eared mother to her roosting tree, an older aspen (popple) that had a large hollow about 20 feet up. The bat had been captured the night before, while foraging about 600 yards away from this tree, and she was fitted with a transmitter. After honing-in on the beeps from her transmitter, researchers would now wait for her to fly out after sunset to confirm the favored tree.
It also turns out the female probably wasn't alone in her roost. The bats often nest in "colonies" or extended families, making each roosting tree that much more important.
"We counted 79 come out of one tree,'' said Morgan Swingen, an NRRI research technician.
There's no lack of trees for the bats to roost in, of course, and habitat isn't the reason northern long-eared bats are threatened. The real problem facing bats is the deadly white-nose syndrome fungus that somehow moved here from Europe a decade ago. But until scientists can get some sort of hold on the fungus -- so far they have not -- it will keep killing bats by the millions. (It does not impact humans.)
In the meantime, researchers are working to preserve as much habitat as possible, to keep non-infected bats as healthy as possible.
It's the same type of care offered bald eagles when they were on the endangered list. While it became quickly clear that it was the pesticide DDT that had caused eagle numbers to plummet by the 1960s and '70s, regulators did more than just ban the sale of DDT. They also protected eagle nesting trees, mating areas and wintering areas from development so eagles had a place to expand once the ill effects of DDT waned.
"'You have to look at all aspects of their life cycle,'' Catton said. "You take a holistic approach."
White-nose syndrome is named for the fuzzy white growth of fungus observed on the faces of infected bats. The disease, which causes wounds to the wing tissue as well as dehydration and starvation, often shows up as unusual behavior, such as flying during the day in summer or leaving caves during their usual winter hibernation.
Since it was first confirmed in the U.S. in a New York cave in early 2007, white-nose syndrome has spread rapidly across the eastern U.S. and Canada, killing more than 5.7 million bats so far, according to the U.S. Fish and Wildlife Service. It's been called the worst wildlife health epidemic in recorded history and is now found in 26 states and five Canadian provinces.
Traces of the disease have been found in the Soudan Underground Mine near Tower and in Forestville/Mystery Cave State Park in southern Minnesota, although no bats have been confirmed to die from the fungus in Minnesota.
In April, however, officials confirmed that diseased bats have now been found as close as Thunder Bay, Ontario, and northern Iowa.
"It's presumed that it will arrive here at some point and we will have to deal with it sooner rather than later,'' Catton said.
Research is underway to try to combat the disease, but so far nothing has worked on a large scale. It has been especially deadly for little brown and northern long-eared bats.
In April, the Fish and Wildlife Service announced it will list northern long-eared bats as "threatened'' under the Endangered Species Act, offering federal protection but a step below full-blown endangered status.
Under threatened status it won't be illegal to accidentally "take" or kill bats when logging or other legal activity occurs, such as farming or clearing utility line corridors. Those activities are specifically allowed under the federal rule.
It will be illegal to intentionally take, kill or disturb bats or their nests, however, except to remove them from buildings.
Logging activities still could face restrictions if they occur within a quarter-mile of a known bat hibernation area. The proposed rule makes it illegal to cut down a known roosting tree during the pup season, from June 1 to July 31, and to clear-cut any forest within a quarter-mile of a known roosting tree during the same period.
That's why finding the bat's favorite roosting trees is important, researchers say.
"It's critical information for this whole effort," Baker said.
Northern long-eared bats are common, although not numerous, in northern Minnesota and Wisconsin. They are found from Maine to North Carolina on the Atlantic Coast, westward to eastern Oklahoma and north through the Dakotas, and reaching into eastern Montana and Wyoming.
The U.S. Fish and Wildlife Service earlier this month announced another round of grants totaling nearly $1 million to 35 states to research bats, monitor populations and, specifically, address white-nose syndrome.
In addition to the netting, banding and roost tree research, scientists also continue to use bat frequency detectors on specific routes across northern Minnesota, a survey method underway since 2009 to find out how widespread bat species are. To some extent, the sonic testing also can plot population trends.
The good news, researchers note, is that the white-nose catastrophe has spurred a new wave of bat research and interest. It's not yet clear if that heightened bat interest is too late.
"We don't know what will happen'' with white-nose syndrome in Minnesota, Moen said. "But we are going to know a lot more about bats either way, and that's a good thing."