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Eastern Gray Treefrogs: An Amphibious Chameleon

(Note: This column was originally published in 2008.)


While inspecting my raspberry patch for damage done by browsing deer, I noticed something hop away into the nearby woods.


The glimpse was enough to identify the fleeing critter as an Eastern gray treefrog, which surprised me. It was midday and the sun was hot. From what little I knew about treefrogs, this one should have been keeping cool inside a hollow log, or resting far aloft in the cranny of an old tree. Judging by its quick departure into the shady woods, the frog agreed.


No one should be impressed I could identify the little frog. I was cheating, actually. Until coming face-to-face with a sluggish, deep-chilled gray treefrog about six weeks earlier, I barely knew of this frog’s existence.


In fact, if the Department of Natural Resources had dragged in Wisconsin’s 11 species of frogs for a lineup and commanded each to sing, I would’ve identified only the bullfrog, leopard frog and Northern spring peeper before changing the subject.


I added the gray treefrog to my ID list in late May on a morning when temperatures hit an unseasonable 37 degrees. While removing my boat’s canvas tarp, I stopped when spotting a frog near the steering wheel. Its gray-green skin with blackish mottling almost matched the console’s light-gray paint.


I marveled that it had somehow climbed up the trailer, scaled the boat’s transom, and then navigated its way to the console. I assume it stopped there when temperatures plunged overnight. After tapping its nose to confirm its metabolism was nearly stalled, I went indoors to retrieve a camera. When I returned, the treefrog hadn’t moved so I photographed it from several angles.


Next I scooped up the little frog and put it down by a stack of firewood. Later I e-mailed two photos to a knowledgeable friend, who said this was nothing extraordinary. He sees gray treefrogs at his house all the time. In fact, he’s learned to double-check his home’s windows before cranking them open on summer nights to ensure he doesn’t squish one.


Gray treefrogs are mostly nocturnal, so humans usually see them on their patios, windows or windowsills, where they hunt insects attracted to outdoor lights. Few sites are beyond their reach. Their toe pads flatten out and emit a light mucus, which creates enough suction to let them ascend vertical glass.


It was also no coincidence the frog blended with my boat’s gray and black-flecked paint-job. The gray treefrog changes colors to match a variety of gray, brown or green backgrounds. If that isn’t enough to disguise them from skunks, opossums, raccoons and other predators, they’re small to boot, measuring only 1.25 to 2-3/8 inches nose to butt.


Even so, the gray treefrog is the largest tree frog in Northern states. It’s present in healthy numbers across most of Wisconsin, and its population has grown steadily since the DNR first organized annual frog-call surveys in 1984. Nationwide, its range extends from southern Ontario to western Texas, across to northern Florida and back to Maine.


And talk about tough. When winter nears, gray treefrogs burrow into the forest duff or huddle inside rotting logs. As temperatures plunge, they produce an antifreeze to prevent their cells from freezing, even though their organs and fluids freeze solid and their heart stops beating. They can freeze and thaw several times before emerging the next spring.


Starting in May and lasting until July, they leave the trees and head to ponds and wetlands to breed. The males court females with endless trilling, and the girls select their mates based on how long the boys sustain their mating songs.


Yes, believe it or not, scientists studied these guys long enough to learn that the gray treefrog’s versions of Frank Sinatra have the best growth rates, making them No. 1 in the natural-selection process.


Some of us remain forever grateful that our partners didn’t embrace such standards.

Eastern gray treefrogs, which are common in Wisconsin, hunt insects at night and can climb nearly any surface. — Patrick Durkin photos


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