“I can see you right now: tromping through the grasses at sunset in your mud boots with your flashlight, thermometer on a string and clipboard. You find a frog and start your survey. ‘So, Mr. Green Frog, just how long have you lived in this pond?’ ”
“You forgot to mention the delightful aroma of insect repellent.” I laughed, but the picture my colleague had painted when I explained that I was participating in a Frog and Toad Survey was not inaccurate. Indeed, I was going to listen to frogs and toads, hoping that they would teach me something with their croaks and snores.
In 1995 school children in Minnesota made headlines when they discovered “deformed” frogs during a field trip to a farm. Since that time frogs and toads have been in and out of the news. Frog and toad populations are declining worldwide, and scientists want to know why.
Frogs and toads are natural bioindicators, species that can tell us a about the environmental health of an area. They have complex life cycle that takes place both in water and on land. Their skin is permeable, allowing the exchange of gasses, and they are sensitive to water chemistry during their egg and larval stages. So, if a water source is contaminated, the local frog and toad populations may decline and eventually disappear or exhibit deformities. Of course to know whether the populations have declined, you first have to know what the “normal” population is. Programs like the Wisconsin DNR Frog and Toad Survey, which have been using a defined protocol to follow frog and toad populations for decades, are essential.
The first time I went “frog listening” was as a biology professor in Iowa. One of my colleagues in the biology department studied ephemeral wetlands and, in particular, the Spadefoot Toad (a species that we do not have in Southern Wisconsin). We waited until sunset and then set out on the farm roads of western Iowa. I was astounded when I heard the racket that the Peepers and Chorus Frogs were making, well above OSHA approved decibel levels! We drove to a field where she and her team had installed automated “listening” stations. There was a large oak tree next to the road, surrounded by water from the recent spring rains.
“Wow—they do snore.” I stuck my head out of the car window, “So this is what a chorus of Spadefoots sounds like.”
“Oh, no. That is not a chorus, when there are this many calling, it’s a congress.”
“A congress of Spadefoot Toads.” Immediately I envisioned Capitol Hill and a bunch of old, overweight politicians snoring away. “Congress is the perfect term for this racket.”
As scientists study the frog and toad populations, they are discovering almost as many reasons for the declines as there are declining populations. At higher altitudes, increased UV light from the thinning ozone layer may be the culprit. In some areas, a fungus that lives on the skin of the frog may be the issue. Some populations decline because of habitat loss, and other populations are feeling the effects of toxins, excess fertilizers and environmental estrogens. In some places, the populations are doing better than we thought. The automated call boxes that my biology colleague and her students installed revealed that Spadefoots like to call immediately after a 2-inch downpour, conditions in which scientists are not often out listening.
When I was pulling weeds from my flower beds earlier this spring, I encountered a Green Frog, camouflaged by some emerging irises. The call of the Green Frog sounds like a plucked banjo string. This fellow wasn’t strumming his banjo yet, and when I picked him up to say hello, he peed all over my glove. That’s okay. I’m glad to know conditions in my neighborhood are inviting enough to keep this little fellow around, because it ain’t easy being green.
© 2008, 2009 Michele Arduengo