AMPHIBIANS ARE ACTIVE IN WINTERTIME

by Whit Gibbons

February 21, 2016

Q: Some frogs are active in the winter where I live in central Alabama, but do salamanders also move around during cold weather? It seems like many amphibians are different from reptiles, which become inactive during the winter.

A: Animals have adapted to myriad environmental situations, and exceptions are rampant in how different species respond to low temperatures. Most, but not all, reptiles become dormant when temperatures approach freezing, whereas many frogs and salamanders have a completely different response. I have seen spring peepers, usually the first frogs people hear in early spring, calling and mating in wetlands margined with ice. My colleague Cris Hagen took a photo of a Cascades frog hopping across snow to reach a breeding site on Mount Rainier in Washington.

One technique used by some species of frogs to deal with cold temperatures is to produce antifreeze in the body, which allows them to survive temperatures below freezing. Most produce glucose in their blood and other tissues to provide protection at temperatures in the 20s. Some species actually do partially freeze, and wood frogs can withstand freezing of up to 70 percent of their total body water. Bullfrogs, on the other hand, are sluggish during cold weather and seldom venture out during winter.

Many salamanders breed in the fall and winter and some can only be found at that time, disappearing into underground retreats when warm spring weather arrives. The tendency of many salamanders associated with wetland habitats to become scarce when springtime temperatures rise and snakes that eat salamanders become active seems like more than a timely coincident.

Among the reptiles, some aquatic turtles are more tolerant of low temperatures than snakes or lizards. My first scientific paper was an observation of dozens of painted turtles that I watched swimming around on the bottom of a Michigan lake covered with see-through ice. Cottonmouths and watersnakes will bask in the sun to warm up on cold days in winter but are positioned where they can immediately retreat into a burrow or under water. Limited observations of cold weather activity by reptiles may be in part a consequence of herpetologists preferring to wait for pleasant weather to go searching for them. Most temperate zone snakes and lizards, however, simply remain immobile underground in the winter. If discovered, they are virtually incapable of escaping.

Q: I've recently noticed that I have a population of either frogs or toads on my pine plantation near Greensboro, Alabama, that can vocalize at temperatures of 45 to 50 degrees. Is this unusual? Do you suppose they are wood frogs? I read that this species is very cold tolerant.

A: Wood frogs can indeed tolerate extremely low temperatures and will often mate and lay eggs in ponds with ice around the edges. Wood frogs are mostly a northern or high altitude species, whose geographic range extends above the Arctic Circle, the only species of frog in the Western Hemisphere that occurs so far north. The southernmost populations of wood frogs that have been reported in the scientific literature, however, are in isolated populations in Alabama and Georgia.

Nonetheless, my guess is that the frogs you are hearing belong to one of the more common species that also breed in the wintertime as long as nighttime temperatures are several degrees above freezing. The most likely one, which is closely related to the wood frog, is the southern leopard frog, a common species throughout most of the Southeast. If you can see one of your calling frogs, you will know for sure. Wood frogs are brown with a distinctive black mask on their face below the eyes, whereas leopard frogs are more greenish with large dark spots on the back, sides and legs. Several of the chorus frog species call in the winter, but their sounds are more chirps and trills than the chuckling of a leopard frog. Toads are mostly active and calling during warm weather.

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