The sun had already gone down as Liza Lehrer began her stroll around the nature boardwalk at Lincoln Park Zoo.
As she passed through the tallgrass prairie, she heard the ducks’ soft quacking, the wind whistling in the air. A few feet ahead, a chipmunk scurried past before darting into the bushes. But Lehrer’s attention was somewhere else.
A pole wrapped in a long wire stuck out of the small backpack she was carrying, a tiny microphone at the tip. Not just any microphone — one that detected ultrasonic echolocation calls in the air, beyond human hearing.
In her hands was an iPad connected to the microphone. She glanced eagerly at the screen to see if a familiar bundle of colorful lines, representing calls above 20 kilohertz, would appear.
That would mean a bat was close.
As Chicago temperatures begin to drop in October, Lehrer, who’s the assistant director at Lincoln Park Zoo’s Urban Wildlife Institute, was wrapping up one of the last bat survey walks of the season. She hoped to record at least one bat.
While eight different species have been spotted in Chicago, Lehrer said that the tricolored, little brown and northern long-eared bats have been increasingly harder to find. Those three species have seen their numbers dwindle over the past years because of white-nose syndrome, a devastating fungal disease that has wiped out hibernating bats.
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The U.S. Fish and Wildlife Service found that the total population of tricolored bats, now a federally listed endangered species, had dropped by 93% in caves and shelters where they hibernate since the first discovery of white-nose syndrome in 2006.
In recent years, these types of walking surveys have grown in popularity in Illinois and across the country to help researchers document bat populations by sending volunteers out with recording devices to catalog the flying mammals in the wild.
“The ultimate goal of this work is to be able to monitor different populations over time of the bats that we have in the Chicago area, but then importantly be able to identify what types of habitat is supportive of these bats,” Lehrer said.
Bats in Illinois have continued to face growing threats. Experts have warned that recent population declines will continue as white-nose syndrome, habitat loss and collisions with wind turbines across the state pose dangers.
By itself, white-nose syndrome led to 6 of Illinois’ 13 bat species being listed as either threatened or endangered, according to the University of Illinois Urbana-Champaign.
Lehrer runs an organization called the Illinois Bat Working Group, which coordinates bat survey walks in Chicago. The group is among several organizations that have been recruiting bat enthusiasts to help protect the species, from the Chicago area to LaSalle County in the north central part of the state.
“We are gathering data on what is living out there … I love finding out just how much diversity there is,” said Hannah Safiran, who lives in Spring Valley and works as a restoration specialist at the Dixon Waterfowl Refuge.
She started going out on bat surveys around LaSalle County this year, after learning about them from another volunteer during a nature training session organized by UIUC.
For Lehrer’s organization, each walk site typically sees a small group of volunteers. The total number of seasonal participants has grown from dozens to hundreds over the last two years as word has spread and Lehrer said she received more research funding, she said.
Lehrer has about 25 monitoring backpacks that she has manually assembles and lends to volunteers trained to use the devices. Each has a microphone, called the Echo Meter Touch 2 Pro Bat Detector. She wraps the microphone around the top of a pole inserted into a backpack to avoid picking up any clothing rustling sounds or handling noise from volunteers.
Since the effort kicked off in 2018, the number of survey sites has expanded from about three to nearly 30 sites across the city, Lehrer said. These include West Ridge Nature, Horner, Humboldt, Montrose and McKinley parks.
“I’ve just seen so many folks who are really interested in learning more about bats and really interested in protecting them,” Lehrer said.
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In Illinois, the bat surveying season usually runs from April to September before the temperatures cool. By then, some bats begin to hibernate while others migrate south to warmer regions.
Since bat calls often last only milliseconds, the recordings can be slowed down to identify the bats in each area based on their unique spectrogram readings, Lehrer said.
After Lehrer collects all the recordings from the year, she uploads them to a bat-classification software. She and another staff member then review each calls’ spectrogram to identify which species they belong to.
Her team relies on the data to monitor bat populations over time and to learn which habitats support bats. She often sends out reports to volunteers and landowners in Chicago recommending ways to create more bat-friendly environments, involving potential changes to landscaping and habitat compositions.
“It’s a great way to get people engaged in doing the work of counting bats,” said Joy O’Keefe, a bat ecologist and associate professor at UIUC. “I think it can also be really informative for people if you’re in an area where there are bats.”
O’Keefe said that bats are crucial to the state’s ecology by acting as natural pest controllers, helping protect forests and agriculture.
Tara Hohoff, an associate mammalogist at the Illinois Natural History Survey, leads another program called the Illinois Bat Conservation Program, which promotes bat surveys across the state. The program works with partners from Champaign County, LaSalle County and the Morton Arboretum.
Hohoff said she’s also seen an influx in volunteers in the last few years.
“I think it shows that the public opinion about bats is changing drastically because I think if we had tried to do this a few decades ago, it would have been very difficult to get people to go out and collect bat data,” Hohoff said “But I think you know we’re realizing how important bats are to our communities and biodiversity.”
Chris Woeltje, 52, has helped conduct bat surveys for Hohoff’s group around LaSalle County over the last three years. He never had prior experience with bats, but grew up as a nature enthusiast and was immediately intrigued when he heard about the opportunity from another volunteer.
He still remembers his excitement after finding out that his recorder picked up on six different bat species during one of his walks.
“There’s so much unknown about the natural world out here,” Woeltje said. “By discovering these species, we’re able to make more educated decisions about conservation efforts.”
Jerry Wu is a freelancer.