The unseasonably mild wind whipped across the barren soybean field as we trudged our way toward what we thought was the location of a calling Illinois chorus frog (Pseudacris illinoensis). A mild sense of paranoia had befallen me. After all, we were four suspicious individuals trespassing across someone else’s property in the dead of night, and my limited experiences with rural landowners has shown that they can be fiercely protective. Guided only by the dim moonlight, Matt took the lead. Following a three hour drive and fueled by adrenaline, the youthful fifty-year-old had his sights set for what looked like a small marsh on the other side of the ag field. His kids, son Alan and daughter Anya, followed - Alan with a somewhat more enthusiastic gait than his sister. And then there I was, trailing the caravan of hopeful frogophiles, using Google maps on my phone to help guide the group. Each time I unlocked my phone I was a little worried that an adjacent landowner was going to spot us from a mile away. But all of that concern quickly dissipated as we arrived at a deep, man-made pond along a dark tree line - the origin of the frog we had heard calling a quarter of a mile or so away.
There are a handful of Illinois anurans that can motivate me to go through such measures to find them. Crawfish frogs, for which I am 0 for 2. Narrowmouth toads and spadefoot toads round out the rest of the group of rare, secretive frogs that are only “easily” observed during their brief breeding seasons. The Illinois chorus frog might be the least known of the group. Much of what is known of the species in Illinois (where the bulk of their occurrences is) comes from Ellen Beltz’s “Distribution and status of the Illinois chorus frog, Pseudacris streckeri illinoensis, in Cass, Menard, Morgan, and Scott Counties of West-central Illinois” (1993). In this paper, Beltz states that the frog was found in only nine Illinois counties, with the core metapopulation situated along the Illinois River. During the last glacial period (about 14,000 years ago but possibly even more recent), retreating glaciers formed sandy ridges and other similar features in the Illinois valley. Later, the gradually warming climate spurred northerly and easterly migrations of many plant and animal species from the south and west. But, very recently in a geologic sense, the climate cooled and became wetter, causing major changes to the landscape. Some isolated sandy areas remained, and with them a collection of unique xeric-adapted species such as the prickly pear cactus, the western hognose snake, and the Illinois chorus frog.
Unfortunately, much of the original sand areas in Illinois have been destroyed. River channelization and row crop agriculture are to blame. Only small, disjunct fragments of intact sand areas remain in central Illinois, threatening the long term survival of this species as well as several others.
Morphologically, the Illinois chorus frog stands out among its peers. Unlike the western (or boreal, whichever you want to run with) chorus frog and spring peeper with which it shares its habitat with, the Illinois chorus frog is robust. Meaty, as I like to say. At only an inch to an inch and half in length, it is a small frog. However, it boasts the most impressive Popeye forearms. It uses these guns to burrow down into the sand, where it spends most of its life. During the 1970s, the late Lauren Brown (RIP) discovered that the Illinois chorus frog even feeds underground, which is a fascinating adaptation to living a fossorial lifestyle. Most frogs burrow or create divots using their muscular hind legs, and feed above ground. What a rebel!
The call of the Illinois chorus frog is distinctive. It’s kind of like a deflated spring peeper. It is unmistakable among the other species of Psuedacris it shares its breeding ponds with.
Amphibian aficionados can hardly wait until March, when the first frogs emerge from their winter dormancy and congregate in breeding pools to ensure the future of their own kind. Pseudacris are early breeders, although some species can remain reproductively active for months (I have recorded chorus frogs near Chicago calling well through June). As the Illinois chorus frog is very selective about its habitat, more effort is required to locate them within their range. This usually involves driving around at night with the windows down, trying to pinpoint the frogs’ locations and then figuring out how to actually get to them on foot.
Illinois chorus frogs occur on protected land, but many of them breed in livestock ponds, low areas around ag fields, and roadside ditches. It is in these latter locations we like to document them. But hearing the frogs is one thing - circumventing their ventriloquy is another. These things can make you nuts. Sometimes it feels like a snipe hunt. You hear a few frogs and you are confident that you are approaching them. Then, the wind shifts and now they sound like they are behind you. You turn back with a puzzled look on your face (don’t worry, it’s really dark and no one can see), only to realize you’re being bamboozled by an animal smaller than your thumb. Eventually you’ll figure it out and you’ll reach their pond, or ditch, or whatever it is they have decided to procreate in. And then all of the effort will have been worth it.
After we zig-zagged our way back to the car, we did visit a few other nearby ditches, and heard a couple more frogs. But the breeding season is just gearing up - more rain is really going to get these guys going. As I write this five days after the jaunt, it’s raining pretty steadily throughout the state and I imagine that tonight, the sandy ditches and ponds in central Illinois are going to erupt.
