Wood Frogs

The duck-like barking sounds of the wood frog are usually the first to be heard by our singing amphibians, as they call out to their mates from their vernal pool breeding sites.  

Wood frogs are found in all types of forests, preferring damp areas like ravines, forested wetlands, swamps and bogs while foraging for a variety of insects and small invertebrates, including spiders, beetles and moth larvae.

 At 2”- 2 3/4” long, wood frogs are identified by a white line above the lip, a dark “robber’s mask” across the eyes, and their color ranges from brown, rust to shades of green…with the ability to change color. Sexes can be distinguished by examining the shape of the webbing found in the hind toes; females have concave webbing, while males are convex.

Wood frogs emerge from hibernation when warm rainfall thaws them. They participate in a yearly migration that brings them to vernal pools for breeding, starting in late February and March. Males search for a mate by hugging other frogs until they find one who is round enough to be carrying eggs. Females lay approximately 1000 eggs, often in the deeper sections of the pools and often attached to other egg masses which in turn are attached to vegetation within the pools. Eggs will hatch in 10-30 days, depending on the temperature. The larval stage, known as tadpoles, feed on algae, detritus, and the larvae of other amphibians…taking a little over a month to mature into frogs. Tadpoles die if the pool dries up prior to growing into a frog.

It is the only frog species that survives above the Arctic Circle, aided by the rare ability to withstand partially freezing. It will not urinate all winter…sometimes for 8 months in Alaska. Microbes in their guts recycle the urea, which begins to accumulated in tissues as winter approaches; and glycogen in the liver converts to glucose as the body begins to freeze. Both urea and glucose act as a sort of anti-freeze, restricting ice formation and cell damage while its heart, brain, and blood flow stop…becoming dead by conventual definition! Cells continue a limited function with a loss of cellular communication. Frogs can survive many freeze/thaw events during winter if no more than about 65% of the total body water freezes. The ability of wood frogs to successfully complete their winter survival transformation is related to the amount of insulating snow cover that exists, as well as how deep a frog is able to burrow into its winter hibernacula. Warmer temperatures bring a slow resumption of function, and they make their way to a nearby vernal pool to shower us with their springtime barking. 

As climate change continues to redistribute snowfall, wood frog habitat that begin to exhibit thinner winter snow cover are likely to suffer population declines.

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