Volunteers Record Ultrasonic Bat Calls to Identify Species

February 24, 2023

An analysis of the bat calls from our 2022 monitoring reveals five species were present across five areas.

The silver-haired bat, hoary bat, eastern red bat, big brown bat, and the evening bat were detected. Monitoring covers different habitat types in transects along the North Shore Channel in Evanston, through Gompers Park, LaBagh Woods and Forest Glen Woods on Chicago's Northwest Side; Gensburg-Markham Prairie in Markham; Joe Louis "The Champ" Golf Course in Riverdale; and Big Marsh Park on the Southeast Side of Chicago. Friends began our bat monitoring work in 2018.

Learn More about Bats on our Podcast about Big Marsh Park

“It’s great to partner with Friends of the Chicago River on this important wildlife monitoring program since Big Marsh Park is a haven for lots of wildlife in the region including birds, insects and mammals,” said Stephen Bell, center director of Big Marsh Park. “Because bats are nocturnal, their presence at the park after hours largely remained a mystery: we assumed they were here, but had no proof to back up that assumption. With this annual program we now know what species of bats call the park home year-over-year, which helps us to gauge the health of the park ecosystem and underscores the success of our habitat restoration efforts.”

Three times during bats' active season, which locally is late spring through early fall, volunteer wildlife monitors, trained by Friends’ conservation programs manager, Maggie Jones, walk preset transects with specialized equipment to capture bats’ ultrasonic calls, which are not audible to humans.

Monitoring begins 30 minutes after sunset in order to capture bats’ natural feeding behavior. Volunteers walk the preset transects for an hour, recording bats’ echolocations utilizing their unique acoustic signature to identify species. The echolocations are recorded to an application on an iPad, which shows the visualization of the bat call as a spectrogram. Because bats have different calls (think of birds having different songs), the presence or absence of a particular species can be determined with high certainty with software analysis. Volunteers follow protocols established by the Urban Wildlife Institute and the Illinois Bat Working Group.

There are eight species of bats in the Chicago region and 13 species of bats in Illinois. Worldwide, nearly 200 bat species in more than 60 countries are considered threatened according to Bat Conservation International. Learn more about bats by listening to our Inside, Out & About podcast about Big Marsh Park featuring Liza Lehrer, assistant director of the Urban Wildlife Institute.

Our thanks to the Urban Wildlife Institute at the Lincoln Park Zoo for their analysis of our bat recordings each season. Special mention to the Forest Preserves of Cook County, The Nature Conservancy, Northeastern Illinois University, and the Chicago Park District for their partnership in allowing our community scientists access to their properties for this data collection.