Great Wisconsin Bat Count See a Decrease in Some Bat Species

Tuesday, October 27th, 2026 -- 8:00 AM

(Sara Gabler, Wisconsin Public Radio) Over 150 scientists and volunteers participated in the Wisconsin Department of Natural Resources’ 12th annual Great Wisconsin Bat Count, tallying 120 roosts and more than 20,000 bats in June and July.

According to Sara Gabler with the Wisconsin Public Radio, Wisconsin is home to eight bat species, four of which remain threatened after this year’s count. The bats were counted as they took flight from their roosts in bat houses and barns across the state.

In the summer months, bats roost in large maternity colonies that are easy to observe. They’re being tracked because ecologists are monitoring the effects of white-nose syndrome, a fatal disease that arrived in the state in 2014.

The bat count results come just in time to raise awareness of international Bat Week, which runs Oct. 24-31. The international festival highlights the critical role that bats play in healthy ecosystems through insect control, pollination and seed dispersal.

Those who want to celebrate can download coloring book pages, learn about the history of forest and cave bats, test bat-friendly recipes (made with ingredients that bats pollinate), or research how to take action in Wisconsin.

Wildlife specialists David Drake and Jamie Nack with the University of Wisconsin-Madison’s Department of Forest and Wildlife Ecology joined WPR’s Lee Rayburn to break down the results of the count and offer advice on how to protect these delicate flying mammals.

There’s still reason to worry about Wisconsin’s bat population after this year’s count. Numbers for both big brown bats and little brown bats were down. Compared to last year, there were about 3,000 fewer little brown bats and 750 fewer big brown bats, Drake said.

Drake attributed the lower numbers to a few possible factors. “The DNR is not quite sure if that count is lower because when the count was going on, weather conditions were not terribly favorable for the count,” Drake said.

Cold temperatures in late spring may have also played a role, especially for pregnant bats. The DNR posited that cold temperatures “may have limited food supply and forced [the bats] to use more energy to stay warm on cool nights.”

The first night of the count occurred in late June, before the baby bats, called pups, had taken flight. The second night of the count was scheduled weeks later, after the pups can leave their roost.

By July, hotter summer temperatures can also affect the bat count, according to the DNR. As soon as the juvenile bats can fly, they may seek cooler places, leaving the location where they were counted previously.

“Big brown bats in general seem to be less tied to specific roosts and readily shift around among sites depending on what’s going on with temperature, time of year, and even parasites. Many who note bats leaving in July often record them returning, sometimes in large numbers, later in the season,” a DNR press release noted.

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