Bats may be one of the mascots of Halloween, but the scariest thing about them is their declining numbers due to factors such as white-nose syndrome.

During the annual observance of International Bat Week, Oct. 24-31, environmental officials in Oneida County are calling on local residents to celebrate and help protect the area’s bat populations through countywide citizen science surveys. Local monitoring feeds into broader regional efforts to safeguard species that provide immense agricultural and environmental benefits.

In Oneida County, volunteer citizen scientists track local bats using two primary methods: roost surveys to count bats during their nightly emergence and acoustic surveys to record high-pitched echolocation calls. To support local monitoring, the Oneida County Land and Water Conservation Department makes acoustic recording equipment available for public use.

Statewide counts look promising

This local survey work aligns directly with statewide monitoring efforts. Wisconsin’s bat population is split into four migratory tree bat species and four hibernating cave bat species. Because cave bats hibernate in close quarters, they are highly vulnerable to white-nose syndrome (WNS), a fungal disease that has led all four cave species to be listed as State Threatened. The disease attacks the bare skin of bats during hibernation each winter. It exhausts their energy stores and leaves them vulnerable to starvation before their insect diet becomes available in the spring.

Despite the ongoing threat of WNS, state wildlife officials report promising news: Wisconsin’s cave bat populations appear to be rising for the third consecutive year.

Fortunately, after experiencing steep declines since 2014 when white-nose syndrome first arrived in Wisconsin, recent Wisconsin Bat Program survey counts show rebounding numbers of little brown bats at some significant roost and hibernation sites across the state. Many of these sites offer ideal conditions for little brown bats and were known to hold large numbers before white-nose syndrome arrived in the state.
Results from the 12th annual Great Wisconsin Bat Count conducted this summer highlight these efforts. Statewide volunteers observed more than 120 roosts and counted more than 20,000 bats, recording 16,865 little brown bats across 57 sites and 3,714 big brown bats across 67 sites.

While this year’s figures reflect a decrease from last year’s totals of 20,944 little brown bats and 4,570 big brown bats, DNR staff remain optimistic about long-term recovery.

Biologists attribute the temporary dip to cool spring weather in May and June that placed extra energy demands on pregnant bats, as well as extreme summer heat that prompted big brown bats to seek cooler locations once juveniles took flight. With no reported pup mortality, experts suggest little brown bat colonies may be reaching local carrying capacity or entering a stable endemic phase of white-nose syndrome with more steady population levels.

DNR conservation biologist and bat program hibernacula specialist Jennifer Redell noted that protecting key wintering sites remains paramount.

“Just a few of Wisconsin’s historic mines are the winter home to a significant percentage of the nation’s little brown bats,” Redell said. “In the spring those bats emerge to spread out across thousands of square miles of forests, fields and neighborhoods in the Midwest. Keeping those hibernating bats safe when they’re here in winter should be of interest to everyone who wants to swat at fewer mosquitoes each summer.”

Important insectivores

Beyond mosquito control, these creatures play a critical role in our broader ecosystem and economy. All eight bat species native to Wisconsin feed exclusively on insects, including agricultural pests like moths, beetles, flies, and mosquitoes. A single bat can consume its body weight in insects each night, protecting crops and forests to save billions of dollars annually while reducing mosquito-borne disease risks. Globally, the world’s 1,400 bat species also pollinate flowers and spread plant seeds.

Staff from the Oneida County Land and Water Department shared some other fun and interesting facts about these fliers, which range in size from the tiny bumblebee bat, weighing less than a penny, to flying foxes with wingspans of up to 6 feet.

Bats also are the only mammals capable of sustained, powered flight. Their wings are made from modified hands with elongated fingers. Besides having good eyesight, many bats also use echolocation — high-pitched sounds that help them navigate and locate prey.

Residents interested in borrowing survey equipment, volunteering, or learning more can contact the Oneida County Land and Water Conservation Department at 715-369-7835 or by email at lwcd@oneidacountywi.gov.