November 29, 2020

A Nightmare for Michigan Bats?

The region’s bats are battling a pandemic of their own
By Hannah Schauer | Oct. 24, 2020

If you’re seeing more decorative bats this Halloween than you saw of their live counterparts this summer, there’s a good reason — though one that’s bad for Michigan bats.

As in many places throughout North America, bat populations in Michigan are declining.

The reason for the reduction in numbers: a fungus named Pseudogymnoascus destructans. It causes a disease called white-nose syndrome — so named for the white, powdery appearance the reveals itself on the exposed skin, like the muzzle and wings, of affected bats.

First documented in New York during the winter of 2006–2007, white-nose syndrome wasn’t confirmed in Michigan in early 2014. By 2016, however, it had clearly made its mark. Surveys of hibernacula (i.e., places where bats hibernate) around Michigan indicated an 83 percent decline in bat populations (when compared to data gathered from surveys \at those sites before white-nose syndrome’s arrival).

Anyone worried about the potential impact cold weather will have on the spread of the novel coronavirus among us will readily understand the swiftness with which white-nose syndrome moves among bats in winter.  

Many insect-eating bats survive winter by going into hibernation, during which they lower their body temperature and use the fat deposits they’ve accumulated during fall to sustain themselves. 
Unfortunately, the places bats like to hibernate, such as caves or underground mines, are also ideal environments for Pseudogymnoascus destructans; it thrives in cold, damp conditions. It also disrupts hibernation, causing bats to prematurely and repeatedly awaken, which quickly depletes their fat reserves and diminishes their body condition — and potential to survive.

“Bats weakened by the loss of fat reserves are unable to replenish themselves due to lack of insects to eat in winter and die before spring,” said Dan O’Brien, a veterinarian at the Michigan Department of Natural Resources’ Wildlife Disease Laboratory. “Infected bats often exhibit abnormal behavior such as flying during daylight hours or gathering outside of caves in cold weather.”

While there is no evidence that white-nose syndrome is infectious to humans, the loss of large numbers of bats may have an indirect impact on people. So why should we care? Because bats are a primary predator of nighttime insects, and large-scale losses of bats could lead to an increase in insect populations, which in turn can cause crop damage or spread other diseases.

Michigan’s DNR has been on leading bat conservation and research efforts for a long time, said Bill Scullon, DNR Wildlife Division field operations supervisor, who adds that “working with partners and researchers is as critical as ever.”

One such effort: the gating of entrances to important bat hibernacula to minimize human disturbance to hibernating bats. Custom steel structures are designed and put up to ensure public safety while allowing the bats to come and go freely from the hibernacula.

“These gates have been built on both public and private lands,” said DNR wildlife biologist John DePue. “Some of these gated sites house large populations of bats in the winter and are important locations to protect.”

Michigan is also one of the few states that participates in field trials of potential treatments to combat white-nose syndrome.

Researchers and students from Western Michigan and Ball State universities, working with the DNR, have been applying an organic compound — derived from shellfish, called chitosan — to bats and the inside of hibernacula. This chitosan compound appears to help bats combat the effects of white-nose syndrome.

Additionally, in some of Michigan’s hibernacula, University of California, Santa Cruz researchers have been treating sites with chlorine dioxide. Treatment is applied to the site when bats are not present to reduce the number of spores that cause white-nose syndrome.

“Chlorine dioxide is used to kill all the fungal spores throughout a mine during the summer, before bats return for the winter,” said DePue. “This will disinfect the site and reduce infection rates and mortality rates.”

DNR staffers, along with researchers from Eastern Michigan University, also conduct annual bat monitoring. Hibernation sites are visited during the winter to learn about places where bats are experiencing higher survival rates, and to monitor population trends.

According to the DNR, installing bat houses can be helpful for bats. Various factors are important when putting up a bat house, including location, color and height. Bat houses should not be in areas frequented by people or domestic animals. To learn tips and tricks for bat houses, check out Bat Conservation International’s website, filled with bat house resources.

Maintaining bat habitat is another way to help bats. Some bats like to roost in trees that have loose bark. Maintaining these types of trees can provide additional roosting locations. Many bats prefer forested areas near a water source, as these places are often abundant with insects.
Those exploring caves or mines should be sure to abide by closures and follow decontamination guidelines to reduce the spread of white-nose syndrome. Avoid visiting these locations during the winter months when bats may be hibernating. Finally, minimize the use of insecticides; they can impact a variety of animal species, bats included.

Want to learn more about Michigan’s bat’s? Check out, where you can learn more about the state’s nine species, threats to them, and even bat-human interactions. 

Happy Bat Week, Batman!
Rather than crabbing about the lack of Halloween parties to attend this year, why not celebrate the week before Halloween in a less crowded way? Oct. 24–31 also brings the annual international celebration of the world’s winged insect-eaters: Bat Week.
Head over to to find Bat Hero challenges for kids, teens, and adults, plus cool videos, a “Bat Brigade” comic book, and a cookbook of treats made with “bat-dependent” ingredients (Mom and Dad, there’s even a recipe for Watermelon Tequila Shots for you!), and lots more.


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