Editor’s Note: This is a guest contribution as part of our Sustainability Scavenger Hunt series. Read more here, and download the fun activity book for families and classrooms!


by guest contributor Jennifer Redell, bat biologist for the Wisconsin Department of Natural Resources

Deep in the quiet and relatively warm but wet cave, I search for bats—my fellow bat biologists and I are on a hibernation survey to determine which species are present, how many, and to assess the effects of white-nose syndrome (WNS) on this site. We trekked through snow and bright daylight to squeeze through a narrow cleft in the bedrock and descend on rope into the black void.

Author Jennifer Redell in a cave and her headlamp shines on a small cluster of little brown bats.

In the darkness of the cave, my headlamp pans the ceiling of the room, highlighting tiny, sparkling bats. Micro water droplets have condensed on their hair and reflect the light like miniature disco balls. They entered the cave in September after storing up enough fat to attempt to make it through six to seven months of winter without starving. Rationed just right, with the help of a lowered body temperature, slowed breathing, and suppressed immune system, a little brown bat will lose one third of its body weight and just barely make it through until spring. WNS causes bats to rouse from hibernation every few days and use up their fat reserves long before insect food is available in spring. Sick bats make their way out of the cave while snow is still heavy on the ground only to starve, freeze, or be picked off by hawks or other predators.

Bats are both cute and, bizarrely, feared. What is understood by a growing number is their role worldwide as critical pollinators, seed dispersers, and controllers of insect pests. Even folks who were given a message to fear bats by misinformed family and friends now understand their vital importance.

Masters of flight and more agile than birds, the most common bats in North America weigh no more than a few pennies. Upon leaving the cave in spring, little brown bats migrate to our forests and fields and our backyards where they are voracious insect eaters whose predatory instincts rival the ferocity of a polar bear. Consuming up to 1,000 bite-sized mosquitoes or their equivalent in just one hour, little brown bats can eat up to their body weight each night. They are the most common of North America’s 47 bat species. With over 1,200 species worldwide, bats make up 20 percent of mammal diversity on the planet!

This winter of 2016-2017 marks what will be the most critical hibernation season Wisconsin bats may ever face. Wisconsin residents can expect to notice the near-absence of backyard bats beginning this summer. The few individuals that return to your neighborhood in the summer of 2017 are likely the survivors of WNS. As I write this, approximately half of our Wisconsin hibernating bats are already dead—they left caves and mines last winter and starved or froze on the snowy landscape, their early emergence from hibernation a symptom of the fungal disease.

A small group of little brown bats cluster on a cave wall to keep warm.

Little brown bats clustered on a cave wall to keep warm. Photo courtesy of the WI DNR.

Last summer our nights were already quieter, as shown by decreased bat-house counts and some monitored colonies that disappeared altogether. Our statewide acoustic (echolocation) surveys showed a 30 percent decline in little brown bat activity in certain areas of Wisconsin’s nighttime landscape. We can expect to see an overall decline of 95 to 99 percent of little brown bats within the coming few years—a loss that mirrors the losses in the eastern half of the United States.

We “bat folks” are all working together as part of a multi-agency-coordinated and collaborative group headed up by the U.S. Fish and Wildlife Service. The search for a treatment is a slow one. Topical skin treatments, decontamination of hibernation sites, a genetic Achilles heel, and vaccination are all being investigated.

The fungus that causes WNS is yet another invasive species, accidentally transported to North America from Europe or Asia. It was first documented in a single New York cave in 2007. It’s now in more than half of the U.S., Canada, and made a jump of over 1,300 miles (farther than a cave bat can fly) to the west coast last winter.

Thankfully, studies of Asian bats with WNS and now North American little brown bats with WNS show that surviving individuals show resistance to the disease. This provides some hope that a few bats will survive the devastation and go on to maintain a very low population level.

So what can you do?

Put up a bat house.

A bat house up on a pole.

No matter where you live, wait no longer to put up that bat house! All animals need food, water, shelter, and space and bats appear to be limited by habitat availability, not food. Find all the information you need to build or purchase one, and where and how to mount it on the Wisconsin Bat Program’s website. Please don’t mount it on a tree where shade cools the bat house too much and predators hang out on branches.

Also check out this video with bat house building expert Ken Borcherding, and learn more here.

Monitor and report bat populations

Individual bats are now very valuable, and bats that continue to reside in your current bat house or move into the one you put up are likely survivors of white-nose syndrome. Conducting your own roost counts and reporting your counts to your state’s bat program helps us understand heir role in healthy ecosystems and inform our actions to improve the future of bats everywhere.

If you live in Wisconsin, help us monitor these special individuals by conducting your own roost counts and reporting roosts on our website.

If you live in other states, search your state’s Department of Natural Resources website for a bat monitoring program.

What else can you do to help?

  • Keep out of caves and other places (mines, tunnels) where bats hibernate from October 1 to May 15. Even quiet activity can set off a chain reaction of bats waking up and burning through critical fat reserves.
  • Maintain and increase the plant diversity on your property to supports a diverse insect population, which in turn supports a diverse bat population. (The answer to this may just mean controlling invasive species as much as possible.)
  • Provide ponds and lakes and help keep them clean to entice bats to your area. The water will also attract bat food: insects. Bats like to roost within a half-mile of a water source, the first place they fly off to each evening just after sunset.

Finally, a recent study published in the Proceedings of the National Academy of Sciences confirms that bats play a significant role in combating corn crop pests, saving more than $1 billion a year in crop damages around the world. Specifically, when bats are kept away from corn crops (using large net enclosures to keep bats out), there are nearly 60 percent more earworm larvae present on plants and 50 percent more corn kernel damage per ear than in control areas where bats are allowed to forage naturally.

Bats need you now more than ever. Your thoughtful and respectful engagement of these awesome and complex animals will help conserve them. Share what you know with family, friends, and neighbors to help prevent acts of direct killing of bats at a time when survival of an individual bat is critically important.


Jennifer Redell with a Malayan flying fox, the largest bat in the world, which is about as long as her arm.

Jennifer Redell with a Malayan flying fox, the largest bat in the world.

Not only a dedicated bat biologist, Jennifer Redell is also the adventurous cave and mine specialist at the Wisconsin Department of Natural Resources (WDNR). She can often be found crawling through muddy caves, paddling water-filled mines, or rappelling into dark crevices in search of Wisconsin’s threatened bat population. As part of the WDNR’s Bat Program, she collaborates with researchers across North America to wage a critical battle with white-nose syndrome, a fungal disease devastating hibernating bat populations. Jennifer’s work has included developing the comprehensive Wisconsin Cave and Mine Catalogue, protecting hibernating bat species under state law, and tracking bats on the summer landscape in order to understand their habitat needs. Redell and the WDNR Bat Program work statewide to routinely monitor bats through acoustic surveys, cave and mine surveys, and summer roost surveys.