On still-chill March nights, when you’re pulling your coat a little tighter, our local amphibians’ cold blood runs a little hotter as the males begin singing their hearts out.
Frog breeding season has begun. If you’re lucky enough to live near a big park with a clean pond or within walking distance of one of our great Cook County forest preserves, for the next few months you might hear a sampling of spring’s greatest love songs.
The first vernal voice rising out of the Chicago wilderness is that of the wood frog (pictured above) in March and early April. A little ice still on the pond doesn’t impede the need to breed: These are the frogs famous for freezing solid—thanks to special proteins and “antifreeze” sugars that prevent fatal cell damage—and then thawing out ready to reproduce.
A wood frog’s call sounds like a two-note quack, or in rapid succession, like a chuckling duck. But your chance to hear these early harbingers of spring is fleeting.
The palm-sized frogs are called explosive breeders because when the weather is right—around 45 degrees with a light breeze and fog or drizzle—thousands can converge at a single breeding pond and fulfill their instinctive imperative in a matter of days or even just hours.
Western chorus frogs settle in for a longer engagement. The most common frogs in our region, they are found in wooded areas and prairies, and they often call during the day. From March to early June, listen for “cr-rr-rr-eek,” like the sound of running your finger over the tines of a comb. In chorus, they sound like a tape loop of rising trills. The sound carries, too. A chorus frog is no longer than an inch and a half, yet its call can be heard for half a mile.
Often calling simultaneously with chorus frogs are the last of the trio of cold-weather breeders, the spring peepers. Another teeny species with a high-pitched voice, the male’s call is a single-note peep, repeated and repeated.
Spring peepers aren’t found in a lot of places in the Chicago area, but where they occur, they are abundant, and the combined sound of hundreds of solitary peeps is of sleigh bells jingling at a near-deafening decibel level. But the calling stops in unison at the slightest movement around the pond. The frogs are especially leery of flying predators, which detect the frogs by their shiny vocal sacs ballooning with each note. When an owl picks off a peeper, the pond can go silent for minutes, until one frog, then another and another, tentatively takes up the call again.
While these three usher in spring, other species keep the music going all the way to summer.
One of our most common frogs is also the most urban. The American toad has expanded its range to include parks and backyards in addition to its natural habitat in forest preserve prairies, savannas and floodplain forests. While he looks like a croaker, he has a long sweet trill that he uses to attract females between April and June.
Our familiar bullfrogs spawn in warm weather, so keep an ear out for the males’ deep, slow bur-rum bur-rum bur-rum between late May and early July.
Frog calls courtesy of the U.S. Geological Survey.
—Karen Furnweger, web editor