Jan 23 2010

Daily Discoveries: A chorus of frogs to bring in the New Year

A spadefoot toad. PHOTO BY: Jamie Rood

A spadefoot toad. PHOTO BY: Jamie Rood

By Jennifer Barbour

I woke to a cold, damp, and cloud-covered New Year’s Day this year. By eight o’clock I had my one year old son, Dylan, sufficiently bundled up and in a stroller: we were off to greet the day with a good long walk. The chirps and chatter of cardinals, chick-a-dees, and warblers distracted me, drawing me in to nature’s beauty. As I neared a wooded wetland, I was delighted to hear a choir of chorus frogs bellowed out. I smiled and we stopped to listen. The sound of chorus frogs brings to mind the sound of a comb as a finger running the length of its teeth. Maybe that’s how it was first described to me, but the similarity is striking. I could see my breath clouding in front of me as I stood and listened and suddenly I remembered that it was the dead of winter. Why were these frogs singing?

Frogs in the Lowcountry do go dormant during our colder months, but unlike their amphibian relatives to the north, they rarely go into true winter hibernation. Hibernation is a common response to the cold winter of temperate climates, but our cool winters and hot, humid summers classify the Lowcountry as a subtropical climate. In response to these mild but unpredictable winter temperatures, frogs and toads in our area have their own strategies for survival.

As temperatures drop, aquatic frogs such as the leopard frog (Rana pipiens) and American bullfrog (Rana catesbeiana) take a dip in the water. Oxygen-rich water allows them to absorb needed oxygen through their skin while they’re underwater. They’ll spend a good portion of their time during cooler months at the bottom of a pond, ditch, or other freshwater wetland, lying on the mud or partially buried in it. The Spadefoot (Scaphiopus holbrookii) and Southern Toad (Bufo terrestris), as well as other terrestrial frogs proficient at digging, will create their winter living space (called a hibernaculum) by excavating a burrow deep into the soil. Treefrogs (Hylidae family) and other species not adept at digging seek out crevices and hollows of shelter found throughout their natural environment. Nooks and crannies of palmetto leaf bases and excavated cavities made by other creatures are good places to look for these frogs.

While many different techniques are used by various species, all amphibians have the same general response to cold weather. Their metabolism dramatically slows down. In freezing temperatures, ice crystals will form in their body cavity, bladder, and under the skin. High concentrations of glucose create an antifreeze effect in their vital organs, keeping them from freezing completely. ‘Frigid’ frogs and toads will stop breathing, and with that last breath, their hearts stop beating; yet they will come back to life as the temperatures rise above freezing, their body thawing perfectly.

As for my serenading chorus frogs (Pseudacris nigrita), they breed in winter, keeping them active throughout our cooler months, especially during warmer rains. Usually found near shallow bodies of water, they can be heard singing both by day and night. Next time your winter walk takes you near a freshwater wetland, keep your ears open for their joyous croons and croaks.

About the Author: Jennifer is a Naturalist with the Kiawah Island Nature Program. To contact her with comments or personal stories, email her at Jennifer_Barbour@kiawahresort.com.

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