Wood frogs spend the winter in a cryogenic-like hibernation.
In early spring, Maine’s woods come alive with the sounds of black ducks. Lots of them.

Only in mid-April, they aren’t ducks, they’re quacking, 2-and-a-half-inch-long wood frogs.

And they’ve got one thing on their minds when emerging from their cryogenic-like hibernation: sex.

Any vernal pool will do, preferably one without fish in it.

“They’re very single-minded about what they’re there for,” said Aram Calhoun, a University of Maine associate professor of wetland ecology and a wetland scientist for Maine Audubon in Orono.

“They’re so skinny and sad-looking when they emerge from hibernation, but I’m very impressed with them because they get right down to business.”

Calhoun said that first night of blind amphibian lust is known as “Big Night” because frogs and some salamander species all move en masse to breeding pools.

“It’s one wild breeding orgy,” she added. “I’ve even seen them mate with other species and other male frogs.”

And all it takes is a couple of brave male wood frogs to reach a vernal pool after hopping about 1,500 feet downhill from upland terrestrial wintering grounds.

Once in the icy water, they start calling – a series of short raspy quacks – and the contagious noise draws in any and all wood frogs within hearing distance, even if the air and water temperature is 30 degrees Fahrenheit or lower.

Following “Big Night,” wood frogs can stay at breeding pools in Maine for up to two weeks.

There, they sing their hearts out to attract females for more frog play before heading back into the woods in search of food and shelter.

Last week and this week are prime times to witness wood frog mating spectacles in central, southern and western Maine. They’re soon followed by spring peepers and gray tree frogs.

“Things are literally just starting to pop in central Maine … . At one pool I watch, (the frogs) are all there on April 15 – Tax Day – and it’s been like that for the past four years,” she added.

Following the calls of wood frogs is a great way to find vernal pools.

“They sound like black ducks in the woods. So walk around on a rainy night, down a country road, and listen for the quacking,” Calhoun said.

Wood frogs normally range in color from pink to brown, with females looking more pinkish brown. But what really distinguishes them is a dark mask that runs from their eye to their front legs.

Last year, Rob Baldwin, one of Calhoun’s students, even discovered that wood frogs can change their color depending on where they are or what the temperature is.

“He noticed it in the field and did an experiment using different colored backgrounds. We’re still finding out new things about frogs, so what we need to do is get government funding for nongame species,” Calhoun said.

But the most dramatic thing about wood frogs, she said, is their ability to freeze solid when hibernating between November and mid-April.

“We barely make it through winters here, and they’re out there in the woods just above the leaf litter. They’re just amazing creatures, and I can’t get over how they survive,” she added.
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