On a late February day more than 10 years ago, a crust of ice rimmed the many small puddles that dotted the woods. Spring seemed a distant promise. But as I listened, a familiar voice reassured me that warmer weather was, indeed, on the way.
The sound came from the hollow below the house. Individually, a single call was difficult to hear. But a chorus of dozens of male wood frogs was easily heard from the house atop the ridge.
The sound was not at all frog-like. It wasn't a croak, a "ribbit," or even a peep. It was raspy. I imagined the conversational "putt, putt, putt" of a flock of turkeys. One field guide describes the wood frog's call as, "like a flock of quacking mallards." When I pointed out the sound to my daughter, she refused to believe the source was a frog. I had to prove it, so we hiked into the woods. Such lessons are rarely forgotten. Experience is a wonderful teacher.
Unfrog-like behavior: A wood frog's behavior isn't very frog-like, either. They emerge in late winter. Ice frequently rings the edges of puddles, ponds and streams when the wood frog chorus begins. That's not too surprising, though, for a species whose range extends north of the Arctic Circle.
Here in the temperate zone, wood frogs inhabit damp woodlands and spend most of the year far from water. They are active during the day and live a solitary life, except during the brief mating season.
In February and March, they gather at ponds and puddles to mate. Wood frogs can measure three inches from nose to tail, but most are smaller. They're best recognized by the prominent black "robber's" mask that extends from in front of the eyes back to the shoulder. Think of it as the raccoon of the frog world. Otherwise, a wood frog's nondescript tan body blends in perfectly with the decomposing leaf litter on the forest floor.
Late winter rain signals the onset of the breeding season. When the air temperature reaches 50 degrees Fahrenheit, male wood frogs move to small ponds and low lying spots that collect snow melt and run-off.
Here the males gather in groups to sing. Within a day or two, females arrive. I suspect no sound in the woods is sweeter to a female wood frog than the raspy quack of a sexy male.
Get started: Wasting little time, males clasp receptive females in a mating embrace herpetologists call amplexus. Females lay hundreds of eggs, which the male fertilizes as she releases them. Typically females release their eggs at communal nesting sites, so masses of thousands of eggs are not uncommon Individual eggs are small black spheres surrounded by a clear gelatinous mass.
An egg mass looks a lot like clear tapioca pudding. The eggs incubate in the water for up to a month, though hatching can occur in less than two weeks when temperatures are unseasonably warm. The eggs can survive a late winter or early spring freeze. The embryos simply stop growing and wait for warmer temperatures to return. Then development resumes.
Advantage: Eggs located in the center of the mass have a distinct advantage. Their temperature may be as much as twelve degrees Fahrenheit warmer than the ambient water temperature, so these eggs are more likely to hatch than those on the perimeter. This may explain why wood frogs breed so early; the eggs laid first occupy the center of eggs masses and are thus most likely to survive.
Wood frog tadpoles measure less than a quarter-inch long when they hatch, and they more than double their size over the next six to 10 weeks. Then they transform into small froglets.
Throughout the summer and into the fall, juvenile wood frogs live on the forest floor near the breeding pool. Females require three years to attain sexual maturity, while males can breed in their second year.
In November the wood frog's life cycle comes full circle. Shorter days and cooler temperatures drive them under ground. There they hibernate until awakened by the longer and warmer days of February and March.