It’s unfortunate that we had to cancel the February meeting due to inclement weather. Amazingly, I’m writing this on Saint Patrick’s Day and we’re once again scraping ice. Given March’s lion-and-lamb unpredictability, it seems odd that a cold-blooded amphibian would choose this time to breed. But the wood frog is uniquely qualified to handle cold weather; it is the only frog found north of the Arctic Circle.
This is because the wood frog has evolved a special technique to survive cold winters; it freezes solid. This involves a number of adaptations to redistribute water in the body, control the rate of freezing, and direct the formation of ice crystals. During the freeze, the frog’s breathing, blood flow, and heart beat cease and as much as 65 percent of the water in its body gradually crystallizes into ice. Scientists are studying this phenomena, as well as the “cocktail” of specialized proteins and glucose which protect the frog’s organs during freezing. (For more information on the research, go to www.exploratorium.edu/frogs/woodfrog/index.html. This page also explains why scientists think this ability evolved quite recently — just since the last ice age.)
As temperatures begin to warm in late winter/early spring, the frogs unfreeze and come out of hibernation. As the ground becomes saturated from snow melt and rain, they begin to migrate toward the breeding ponds. At night, during the first heavy downpour in February or March, you can find them moving en mass. Once at the pond, the males begin calling, sounding like ducks quacking or people chuckling. (To hear the sound, go to [URL no longer active].)
You may remember two years ago, Robin Loube heard the frogs and wrote an article in the Northwood News, “Adventures in Frogland.” At the time, however, we weren’t sure if we were looking wood frog or leopard frog tadpoles, because their breeding periods overlap. This year I heard the frogs myself and saw some of them with their distinctive “robber’s mask” and “white mustache.” For lots more information on the wood frog (as well as great biodiveristy information), go to animaldiversity.ummz. umich.edu/site/accounts/information/Rana_sylvatica.html. By the time you get this newsletter, the tadpoles should be well along; wood frog tadpoles can complete metamorphosis in just two months. Do walk down to the vernal pool along Northwest Branch and take a look. This has now become part of my ritual “welcoming spring” activities, just like looking for the first robin and the first wildflowers.
Amphibians are important environmental sentinels because their porous skins make them vulnerable to pollution and because, to survive, they need a variety of connected habitats. They need the woods to forage in during the summer and fall, they need leaf litter or old stumps to hibernate in during winter, and they need vernal pools to breed in during the spring. Thus, it does frogs no good to preserve the wetlands without the forest uplands, and “cleaning out” fallen trees or raking up leaves destroys vital habitat.
Wood frogs seem to be doing fairly well in much of their range, but individual populations have suffered from suburban development filing in wetlands, cutting down forests, or building roadways which keep the frogs from reaching their breeding pools. To see how populations are doing in Maryland or to become a frog monitor, check out Frogwatch at www.aza.org/frogwatch [URL updated from printed newsletter].
So let the wood frog remind you that there is much that is precious as well as entertaining in our local environment. Come and join us for the spring creek cleanup and the Charlie Pritchard Memorial tree planting (which will be scheduled for later in the spring) and help us keep our local environment strong and healthy for woodfrogs and other living things. ■
© 2007 NFCCA [Source: https://nfcca.org/news/nn200704b.html]