In any neighborhood in spring where there’s a spit — or maybe a bit more — of water, you might hear an unusual sound as if someone were rubbing a thumb against the teeth of a comb. The sound crescendos, then fades away, only to start up again.
It’s coming from the chorus frog, one of the first thumb-sized frog species to begin mating in spring. As soon as a small pond’s edge is free of ice, the chorus frogs awaken from their slumber at the muddy bottoms to start mating. Actually, they are nearly frozen during the winter and “thaw out” when it’s time to procreate.
Frog species more commonly vocalize and are more active at night, but chorus frogs often sing during the day, bringing nature in focus to even the most casual observer.
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In the woods, the chorus frog choir will lead you to what’s known as an ephemeral pond or temporary pool of water. They also frequent marsh edges, but you won’t find them in any body of water where there’s fish. They’re so small they’d be swallowed up before they could mate and lay eggs.
Chorus frogs belong to the tree frog family. These 1- to 2-inch-long amphibians often have suction cups on their feet to crawl up a tree. Even though chorus frogs are in the tree frog family, they don’t spend any time in trees.
They begin their choruses in February in northern Illinois, and are typically in full force in late March and into April.
I often try to get a look at chorus frogs. But as I walk to the edge of the small pond where they are singing, they just stop, alert to the presence of intruders. They bury their heads in the mud until the intruder leaves.
I’ve never had the fortune of seeing a chorus frog inflating its throat to look like someone is blowing a bubble while chewing gum. That helps make the sound louder and attracts females. It’s a technique many frog species use during mating season.
After chorus frogs mate, females lay clusters of dozens to hundreds of microscopic eggs on vegetation below the water’s surface. I’ve seen these clusters, which are about an inch long, on temporary pools of water in woodlands in early spring. It’s like finding a hidden treasure. The eggs hatch in a week, and then it takes six to eight weeks for the tadpoles to become adult frogs. Tadpoles love munching on algae.
Until recently, experts have referred to the chorus frogs we hear in northern Illinois as western chorus frogs. Today, they’re identified as boreal chorus frogs, according to the Chicago Academy of Sciences.
According to one account, the boreal chorus frog and western chorus frog look similar with three, often faint stripes on a brownish to greenish back and a dark band across the eye and side, but the boreal has shorter legs than the western.
There’s also a threatened Illinois chorus frog that lives in rare sand prairies in the west-central and southwestern part of the state, but not in northern Illinois. These three species look and sound alike, although some discerning herpetologists can identify all three by their calls.
A less-common tree frog in northern Illinois is the spring peeper, which gives tinkling bell sounds within woodlands mostly at night. It’s just as tiny and difficult-to-see as the chorus frog, and more common in farther southern Illinois. I’ve spent many a glorious evening in southern Illinois listening to chorus frogs and spring peepers deafen the air with their calls.
Come May, American toads start calling around ponds creating a constant whirring sound. In late June, the bullfrogs begin their low, rumbling serenades, from larger and permanent bodies of water. They are much larger than the chorus frogs and peepers, and much easier to see.
The presence of frogs can indicate a healthy ecosystem. Their permeable skin makes them sensitive to water pollution. Frogs have been on Earth for at least 200 million years, living alongside dinosaurs. To hear the sounds of the common and rare frog species that sing in northern Illinois, visit frogsurvey.org and click on Chicagoland frogs. Then go out to some nearby pond and listen for nature’s seemingly invisible spirits.
Sheryl DeVore has worked as a full-time and freelance reporter, editor and photographer for the baiduhai and its subsidiaries. She’s the author of several books on nature and the environment. Send story ideas and thoughts to [email protected]