Thursday, April 21, 2011

Adirondack Amphibians: The Wood Frog in Spring

The awakening of the many forms of life that passed the winter in a deeply dormant state begins with the melting of the snow, the retreating of the ice sheet covering our waterways, and the thawing of the soil. Because of fundamental physiological differences among the species and the various preferences that each creature has for a wintering site, some animals are quicker to respond to the onset of favorable spring conditions than others.

In the forested regions of the North Country, the wood frog is among the first to return to an active state and announce with a distinct chorus of voices that spring has come to the Adirondacks.

Unlike other frogs in the Adirondacks, the wood frog does not spend the winter embedded in the muck that covers numerous bodies of water. Rather, this amphibian burrows deep into the leaf litter that covers the forest floor to protect itself from the frigid conditions of this long season. Also, unlike many other cold-blooded vertebrates, the wood frog fails to get below the frost line.

This small, forest dwelling frog with the black mask across its face is among the very few forms of vertebrate life that can experience freezing without perishing. The body of this frog has adapted by producing several substances that allow for a lowering of the freezing point of the water molecules within its body.

Additionally, even if the actions of these compounds fail to prevent ice crystals from forming, the wood frog will not die. With the formation of ice in its body, the wood frog’s heart stops beating, its blood no longer circulates throughout its systems, and oxygen fails to be delivered to its cells. In this type of cryogenic state, the wood frog can remain alive throughout the winter and awaken once its body warms to a temperature that is above freezing.

As soon as the upper layer of soil thaws, releasing the wood frog from its icy tomb, it spends a few days acclimating to an active state before heading to the small, vernal pool of water that serves as its breeding ground. Upon arriving at such a seasonal body of water, the males begin to announce their presence by emitting a clacking noise that is described by some as several ducks that are not quite “on-key”.

Within a span of a few days, such small bodies of water may contain dozens of wood frogs. While these amphibians can be heard anytime of the day, late afternoon is when more voices are added to the chorus, and by evening on those occasions when the temperature is well above the freezing point, every male is contributing to the unique noise that can carry for nearly a hundred yards. Additionally, the intensity of this sound increases during times of warmer weather. Sunny days which can elevate the temperature of these small, seasonal pools can also make the wood frog more active and vocal.

While some amphibians, like the spring peeper, persist in announcing its presence for well over a month, the wood frog seldom remains in its breeding surroundings longer than a week to ten days. Shortly after the last females have had their egg masses fertilized, these temporary occupants abandon the pools and begin their travel to their summer ranges. Wood frogs are reported to migrate up to a half mile to reach a favorable spot on the forest floor in which to spend the summer.

Spring is a season of sound in the Adirondacks. While birds have the most musically complex songs, and the most melodious calls, the voices of several amphibians add to the diversity of this springtime, vocal ritual. It is impossible to state which amphibian produces the most appealing mating call; however, it is certain that the love serenade of the wood frog is the first to grace the air and signal that the spring peepers will soon be calling here in the Adirondacks.

Tom Kalinowski has written several books on Adirondack nature and is a regular contributor on natural history here at the Adirondack Almanack.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.




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