Bats are one of the smallest and most threatened mammals in the United States. The species has been hit hard by a fungus called white-nose syndrome. It first appeared in New York in 2006 and Wisconsin saw the impact about eight years later with a steep decline in the bat population.
Bats play an essential role in our ecosystem. They’re pollinators and seed dispersers and eat many pesky insects — just some of the reasons researchers are hoping to build the population back up.
This past August, a team of researchers, some from Virginia Tech and others from Wisconsin’s DNR, huddled within a screened tent about an hour northwest of Milwaukee.
This wasn’t an evening picnic. Everyone was gloved and dressed in hazmat suits. They trap the wee creatures in fine nets or in what’s called a harp trap.
Its two strands of fishing line funnel the bats gently into a container bag. The researchers want to know how these survivors of the white-nose syndrome are doing., carefully handling the little brown balls of fur – deftly and quickly.
Before suiting up, J. Paul White helped set up the trap. White is a mammal ecologist and team lead for the DNR bat program.
“It’s a way to funnel bats through a particular area and then they fly through sideways … and then just glide right down into our containment bag where we can then grab them pretty effortlessly, “ White says.
Late August is an action-packed time for bats. White walks to a spot where bats will soon be swirling up and out of their underground cave.
“Typically, what they’ll do is the first three or three-and-a-half hours of the night, they’ll be feeding quite heavily … The females often have pups that they have to feed and nurse; if it’s a male, they’re less restricted, right? They don’t really have any responsibility. If it’s too cold, they might just come back in and go into torpor,” White says.
It's also mating season, “so an incredibly important time,” White says.
In the late 1800s, this site was home to an iron mine. Since being abandoned, bats have made the cold cavernous space hibernaculum, where they winter in their torpor state.
"We have no idea when bats moved in but by the '80s and '90s it was known as an important site," says Jennifer Redell. She’s a conservation biologist as well as a cave and mine specialist with the Wisconsin DNR.
"There were 143,000 [bats] — one of the largest little brown bats hibernation sites in the eastern half of the U.S.," Redell says.
White-nose syndrome has killed 90% of Wisconsin’s little brown bats, along with Wisconsin’s other hibernating bat species.
On this late summer night the team would only net 100 of the creatures. "This is the end of August. They’re leaving their summer roost. Some bats migrate to Minnesota and Tennessee, but these bats go into a cave or a mine. They fly around in and out of entrances at night. It’s called the fall swarm," Redell says.
Redell and the rest of the team weigh the bats, estimate their ages, and fasten a tiny aluminum wing band before releasing the bats. They also check for the presence of the white-nose fungus. The site is significant to bat research and to Redell personally. Her husband, the late Dave Redell, did his master’s work here. Dave became the first bat ecologist for the state Department of Natural Resources.
"He got our bat program going. He developed a system of using infrared beams to shoot across the entrances to count bats going in and out," Redell says.
She says Dave also puzzled out what triggers bats’ emergence in spring.
"It turns out it’s the reversal of air flow in the site. So the chimney effect of warm underground air switching over the nights and days warm up. And that sends the bats out on the landscape," Redell says.
She points the latest technology. “You can see the PIT tag antennae that you see mounted across the bat gate,” Redell says.
PIT stands for Passive Integrated Transponder. The tags are tiny microchips, and researchers gently inject them just under the skin between the bat’s shoulder blades.
"That pings when the pass through antennae set up to capture bat movement. The technology is not unique to the state, but Wisconsin has expanded to both summer and winter sites to record movement between two habitats," she says.
Redell says the information is a game changer for bat researchers — allowing them to monitor bats year round.
“We’ve only had a few years of readers in an intensive PIT tag effort, but it’s special and somewhat unique to Wisconsin to have such a big network at our most important sites, and we’re starting to make specific connections between this bat roosting at this address in a bat house in summer, and then it’s coming to this specific mine in winter,” Redell says.
Scientists have learned some bats may make trips from summer roost to in their hibernation spots several times between May and August before settling into hibernate for the winter.
Redell says they’re also learning more about the importance of cold, wet hibernation sites.
"We know cold is definitely important and we’re starting to figure out wet is really important as well. The fungus doesn’t grow as well and bats seem to do a little better. Their populations are growing slowly at some sites," she says.
Redell marvels at the partnerships that have evolved, especially with scientists from Virginia Tech. They work side by side with the DNR team throughout the year, as part of what Redel calls "short, really intense field seasons."
She says they’re all determined to do what they can for these amazing creatures. Redell says look at the females —they’ll continue to mate throughout the winter, occasionally waking up from torpor. The female stores sperm until spring. It’s the perfect evolutionary strategy because she comes out having lost 1/3 of her body weight, energy depleted. She books it straight to a summer roost site, gets pregnant, and then gives birth around June 1,” Redell says.
Each female bat produces only one pup. It has around three months to acclimate to the world before they all head back to hibernate. “Before having to deal with having no food all winter,” Redell says.
As the pace picks up that evening, a pile of carefully folded paper lunch bags quiver at Redell’s feet. Each contains a bat about to be inspected.
The team limits their time and contact with each furry creature. “To prevent stress on the tiny wild animal, we try to work with them quickly and somewhat quietly before sending them away again,” Redell explains.
The bats need all the help they can get.
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