The Wisconsin Department of Natural Resources’ frog survey season is off to a hopping start this spring.
Each month of the season, volunteers across the state spend an evening listening for different frog and toad species.
This allows the DNR to map and track the amphibians.
WXPR’s Erin Gottsacker went with a volunteer to listen for the frogs. Here’s what she heard:
When the sun goes down on a chilly April evening, the volume of croaking frogs comes up.
“This is really special,” Citizen Scientist Dorothy Skye whispered. “I think we’re getting both the chorus of the peepers and the chorus of the boreals.”
For one evening a month each spring, Skye volunteers for the Wisconsin DNR to drive an established route by big lakes, small ponds and shallow swamps.
At each body of water, she stops her car, rolls down her window and listens.
She tries to identify which species are present at each spot by listening to their calls.
“Boreal chorus are like running your fingers down a fine-tooth comb. Wood frogs sound like a duck,” she explained.
She also gives a rough estimate of how many frogs of each species are hanging around.
The DNR has a system for this. On a scale of one to three, volunteers rank the frog calls they hear.
One means the frog calls are few and far between. Three means they’re constant.
“I’m going to call that a one because they’re quite distinct,” she said, after listening to frog calls on the shore of a deep lake. “You can kind of start to tell that there are two different frogs coming from different directions.”
Volunteers from all over the state collect data like this.
They also record how windy it is and the temperature of the water.
Then they send all that information to the DNR, which has been collecting the same data points for almost 40 years.
Andrew Badje is a DNR conservation biologist. He’s one of the people who analyzes the information and decides what to do with it.
“What we’ve done is figure out where all of our species are in the state,” he said. “Before that we didn’t really know what kind of habitats they were using. Then, you can figure out how each species is doing, if it’s stable, if it’s increasing or decreasing. So that’s really cool.”
Wisconsin was the first place in the continent to do a survey like this, so the state has a lot of uninterrupted data.
By tracking it over so many years, the DNR has found that some frog and toad species are doing pretty well.
“Wood frogs, [boreal] chorus frogs are relatively stable over the years. Spring peepers, to be honest, it seems to be climbing over the years, or at least the sites we’ve added are more heavily dominated with spring peepers, one of the two,” he said.
However, not every species is flourishing.
“The mink frog, which is a Northwoods species, has slowly been on a decline,” Badje said. “Call it climate change, call it whatever you want. My guess would be, over time, that’s going to be a species we really want to keep looking at.”
Because of the data so many volunteers have collected over the years, the DNR is aware this decline is happening.
As a result, they can take steps to protect and conserve species like the mink frog.
That’s why Badje considers the frog and toad monitoring program a success.
“We can monitor 12 species pretty easily just by getting volunteers involved,” he said. “And in the process, they do something fun that they appreciate.”
Back on Dorothy Skye’s frog survey driving route, the wind picks up and it starts to lightly rain.
She only has a few more stops to complete the route this evening, but she’ll be back in May to listen again.