Many of us have taken to the outdoors recently. I don’t have to tell you why. It’s a great way to get exercise and still maintain social distancing. So if you’ve been out walking, you might be asking yourself, “What’s all that quacking going on?”
No, Daffy is still safe in cartoonland and mallards are not quacking in the middle of woods. For one thing, it’s not their usual habitat.
You are hearing the mating call of the male Wood Frog, Rana sylvatica, a brown, dark-masked amphibian with a fascinating life history. In the early spring, sometimes as early as February, when the first “warm” rains come with a temperature above 44 degrees F (7 degrees C), wood frogs crawl out of the leaf litter and head for vernal (literally meaning spring) pools. These often temporary and usually shallow pools are found in forests in the Appalachians, New England, and most of Canada and Alaska. By using these temporary pools, the frogs avoid being eaten by fish.
These frogs have been semi-frozen in the leaf litter all winter. In the late fall when temperatures drop to freezing, special proteins cause the water in the frog’s blood to freeze first. This pulls out most of the water in its cells. While this is happening, its liver is pumping sugar (glucose) into the cells. This “anti-freeze” keeps the cells from freezing. Everything then shuts down—no beating heart or other functions!
This unique adaptation has enabled wood frogs to survive as far north as above the Arctic Circle. Scientists are studying this freeze-and-thaw cycle and hope what they learn can help with human organ transplants.
Back to the quacking. Check out the Wood Frog’s call and others on the Yale Peabody Museum Vertebrate Zoology Collection’s Online Guide to the Reptiles and Amphibians of Connecticut. After attracting a mate with its calls, the male Wood Frog externally fertilizes her eggs in the vernal pool. A female will lay an average of 1,750 eggs. Once the eggs have hatched, it’s a race for the tadpoles to develop into froglets and get out of the water before the vernal pool dries up in the heat of summer.
Click here to see the interesting findings that David Skelly, Peabody Director and Frank R. Oastler Professor of Ecology, and his graduate students have made in their study of wood frogs. Photo by Peter Paplanus from St. Louis, MO/ccby http://creativecommons.org/licenses/by/2.0