Bats in the growing darkness

Emily Stone

Darkness encroaches on either side of my days. The growing shadows reveal new wonders and old friends, as does the lengthening daylight of spring.
When dusk falls before bedtime, I can step outside to watch stars sparkle across a moonless sky and northern lights dance above a silver lake. The dark collects everyone from their outdoor adventures, and gathers them inside for the evening. It feels right to eat dinner at six o’clock instead of eight-thirty.
When my alarm beeps before sunrise, dawn accompanies my morning yoga. It is harder to get out of bed in the dark, but gray light soon eases the entry into wakefulness, and flaming pink skies reward even the not-so-early bird. On weekends, the sluggish sun finally allows me to sleep in.
One morning last week, while watching that gray light turn lavender and pink, I caught a glimpse of movement through gaps in the silhouetted trees. Dark shapes that I’m usually too sleepy to see fluttered back and forth across the chilly dawn. Bats!
I wasn’t able to identify the species of bats zipping through the yard, but no matter which of Wisconsin’s seven bat species they are, fall is a challenging and potentially dangerous time. With amazing powers of echolocation, they are certainly comfortable in the increasing darkness, but not the increasing cold.
Little brown bats, a type of cave bat, are widespread and common in the Northwoods. They spend their summers hunting insects near water, and roosting in warm spaces like wood piles, trees, and your attic. Bats enter a period of torpor each day, where their metabolic rate and body temperature drop. Roosting in a warm environment allows them to keep their body temperature at a high level even while saving precious energy.
Through the winter, little brown bats also need their environment to provide a stable temperature. Lower temperatures that stay above freezing are ideal conditions that allow bats to slow down their metabolism and conserve energy. Winter periods of torpor last longer, but bats will still wake up in order to groom themselves, and sometimes to get a drink.
This time of year, little brown bats, big brown bats, northern long-eared bats, and eastern pipistrelles are all heading for the caves and old mines that serve as their hibernacula. According to Brian Heeringa, biologist with the US Forest Service in Washburn, our bats have already begun to move (toward the UP of Michigan and SW Wisconsin), and the ones I saw may be migrating through from even farther away.
While the caves that provide bats with shelter are integral to their survival, those same caves may now house the biggest threat to their existence. White-nose syndrome (WNS), a devastating disease caused by a soil fungus, is causing unprecedented mortality in cave bats across the eastern United States.
The fungus affects bats’ skin. Wings are especially vulnerable. Noses become whitened, too. Being cleanly creatures, infected bats wake up more often to groom themselves, thereby depleting their energy stores and becoming dehydrated. Up to 95% of bats in infected caves die over the winter.
WNS was discovered in southwestern Wisconsin just last spring, and only infected 2% of the bats in one cave. There are no confirmed sites in Minnesota…yet. Its spread is inevitable, though, and it is causing the most precipitous decline of North American wildlife in recorded history. This winter, the WI DNR will continue to monitor all the known hibernacula in Wisconsin for WNS. In mid to late winter, biologists will be swabbing noses, taking soil samples, and simply looking for signs of the fungus. You can check the spread maps at for up-to-date information.
What I find fascinating—and hopeful—is that in Europe, where the fungus originated, bats are not extinct. Their populations have adapted to being less dense, with larger individuals. Lower densities probably slow the fungus’s spread, while the larger bats’ greater energy stores seem to allow them to wake up more often and groom away the fungus. Perhaps our bats will adapt in the same ways.
Presently, only bats that hibernate in caves are infected by WNS. Wisconsin also has three species of tree bats that migrate south for the winter and have not been affected by WNS. Hoary bats, silver-haired bats, and eastern red bats fly hundreds of miles south to the balmy weather in Mexico, Florida, or even Illinois. These bats face a different hazard, however—wind turbines.
Being curious mammals, bats seem to be attracted to wind turbines. During migration, many bats may travel through wind farms.  Getting too close either results in death by impact or in death by barotrauma. Barotrauma takes place when bats enter the area of low pressure just behind the spinning blades. The pressure differential causes the bats’ lungs to fill with fluid. Power companies can help by turning off the blades during the bats’ most active periods, which usually coincide with low wind speeds anyway.
Bats are amazing creatures, with many fascinating adaptations. I would much rather write about those adaptations than about the potentially devastating threats bats face. But if the bats are to survive these challenges and be there amaze and fascinate us in the future, they need our help and support now. We can all help protect their summer habitat and food sources, so that bats can survive this growing darkness and time of change to fly again in spring.
Visit your state’s DNR website,, or the Museum’s current exhibit “Nature’s Superheroes,” for information about how you can help!

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! The current exhibit, “Nature’s Superheroes—Adventures with Adaptations,” opens in May 2014 and will remain open until March 2015.

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