Wisconsin bat facts to share this Halloween

With Halloween just around the corner, spooky symbols of the holiday abound, including bats.

That’s coincidentally so International Bat Weekcelebrating the role of bats in nature. Chance? Maybe not.

Bats’ connection to Halloween goes back to Samhain, an ancient Celtic festival where large bonfires were built to ward off evil spirits. Bats flew near the fire, interpreted as the spirits themselves. Then of course there are vampire bats, which drink blood (although rarely that of humans). Over time, these flying, winged creatures of the night have become synonymous with the spooky season.

Over the past decade, the hundreds of thousands of bats living in Wisconsin have faced a real, terrifying situation: the emergence of white-nose syndrome, a fungal disease that is having devastating effects on the state’s bat population.

Now there are small signs that these numbers may be recovering. Here’s what you need to know about Wisconsin’s bats and how you can help them thrive.

What types of bats live in Wisconsin?

There are eight species of bats in Wisconsin, split into two groups: cave-dwelling bats and tree-dwelling bats. They all eat insects.

Tree-dwelling bats, including in Wisconsin the silver-haired, eastern red, gray and evening bats, migrate south for the winter, usually leaving in September and October. Wisconsin’s cave dwellers — big brown and little brown bats, the most common in the state, as well as tricolor and northern long-eared bats — spend their winters in caves or mines.

All these species face threats to their survival.

Where are bats found in Wisconsin?

During the summer months, bats are found throughout the state. During the winter, the tree-dwelling bats have disappeared and the cave dwellers look for hibernation sites, which differ based on their species.

For example, the vast majority of the state’s little brown bats congregate in three hibernation sites, says Jennifer Redell, a conservation biologist and cave and mining specialist for the Wisconsin Department of Natural Resources. One does Neda minea former iron mine in Dodge County, and the other two are former frac sand mines in Pierce County. Neda Mine is one of the largest bat hibernation sites in the Midwest.

There are up to 200 other hibernation sites, such as other mines, natural caves and railway tunnels, where small numbers of other cave-dwelling bats spend their winter.

Big brown bats are more tolerant of cold and dry conditions, Redell said, so they sometimes don’t hibernate until December — and when they do, they’re more likely to hibernate in people’s homes.

What is white-nose syndrome and how has it affected Wisconsin bats?

White-nose syndrome is a fungal disease that kills bats in North America. The species is named for the powdery white fungal growth on the wings and snouts of infected bats. The species was first found in Wisconsin in 2014 and has had a catastrophic impact on the state’s bat population.

Little brown bats in particular have suffered the most, Redell said. Since the disease spread in Wisconsin, the DNR is detecting 90% fewer echolocation calls from little brown bats when they are active during the summer months.

At the two roosts in Pierce County, she estimated that the bat population dropped by 80% after the onset of white-nose syndrome, from about 150,000 to about 30,000. (It is difficult to count bats in the Neda mine because of the mine’s deep cracks and crevices.) The number of bats in some of the smaller hibernation sites has dropped to zero.

But the numbers have looked more reassuring in recent years. Over the past three winters, Pierce County sites have housed about 60,000 bats, Redell said, and during the summer volunteers count larger numbers of bats leaving their summer roosts, especially along the Mississippi and Wisconsin rivers.

What is the reason for the improvement?

“Bats have been around for more than 50 million years,” Redell said. “They are very adaptable… we have some hope that their adaptability will help them in the era of white-nose syndrome.”

There could be less mold in the environment as the years go by, she suggested, or frac sand — a desiccant — reduces mold loads in the mines when the bats aren’t there.

What other threats do bats face?

Because the fungus that causes white-nose syndrome does better in warmer conditions, warming temperatures at hibernation sites due to climate change could have negative effects, Redell said.

Bats are also experiencing habitat loss — not so much the loss of forests and caves, she said, but from being evicted from homes, sheds and other buildings. Wind turbines can also harm bats as a result of collisions.

And yet bats have a marketing problem: some people find them scary and don’t want them around. This could lead to immediate killings, Redell said.

Why are bats important for people and the environment?

Perhaps bats’ greatest blessing to humans lies in their diet. A single bat can eat thousands of insects per nightthus ridding the air of mosquitoes and other pests.

In 2018, a study from UW-Madison The analysis of bat feces showed that little brown bats in Wisconsin ate 17 different species of mosquitoes, including nine that carry West Nile virus. The same study found the DNA of 24 different agricultural pests in the poop – confirming the estimate that bats are saving Wisconsin farmers hundreds of millions of dollars a year on pesticides.

Although not native to Wisconsin, nectar-feeding bats also help pollinate crops. They are the only pollinator of the agave plant, a key ingredient in tequila.

How can you help Wisconsin bats?

Start by building a bat house, which will provide a safe summer roost for bats, Redell suggested. Grow plants native to Wisconsin, which in turn attract native insects that bats eat.

If you need to “exclude” bats from a building, do so in the winter, when they are not using their summer roosts. Avoid this during the maternity season, which runs from June 1 to August 15.

More generally, Redell said people should take steps to protect access to caves and mines and stay out of them during the bat hibernation period, which in Wisconsin begins on October 1 and ends on May 15.

“The biggest and best thing anyone can do is advocate for bats, especially when someone says something disparaging or spreads misinformation,” she said.

Where can people see them safely?

During the summer months, a few state parks are home to significant colonies of bats, Redell said, including Peninsula State Park in Door County, Devil’s Lake State Park in Baraboo and Yellowstone Lake State Park in Blanchardville.

Sometimes the parks host special programs, Redell said, but it’s not necessary to see them: Stick around about 30 minutes after sunset, and every night the bats come flying out of their “bat apartments,” she said.

To respect them, keep a distance of 15 to 20 feet, do not use flash photography, and speak softly or not at all.

Madeline Heim is one Report for America corps reporter who writes about environmental issues in the Mississippi River basin and throughout Wisconsin. Contact her at 920-996-7266 or [email protected].