Herps over winter
By STEPHEN C. FRIET*
MAMMALS AND BIRDS generate their own body heat and maintain a fairly constant body temperature. They are endotherms (warm-blooded is not entirely accurate, since their blood, as shown with woodchucks, can be very cold). Amphibians and reptiles are ectotherms, meaning they must obtain energy from external sources to regulate their body heat (needless to say , their blood is not always cold). Because these animals, known collectively as herptofauna (herps, for short), rely on outside sources for their warmth, they have evolved some of the most amazing strategies to protect themselves from the cold of winter. Herptofauna go through changes in their bodies' activities during winter. All of these animals forgo eating, because it takes to much energy for what it is worth to digest food. They become inactive, though all are still capable of activity. The so-called "cold-blooded" animals have adapted well to winter.
The Maritimes region boasts a diverse herptofauna, comprised of six salamanders, one newt, eight frogs, one toad, four turtles, three sea turtles and five snakes. Because of our northerly latitude, we have relatively long, cold winters by herpetological standards. The amphibians and reptiles here use a phenomenal number of overwintering strategies to survive to the next breeding season in the spring.
Many amphibians and reptiles live the winter out on the land. They use one of two strategies: freeze-avoidance and freeze-tolerance. Freeze-avoidance is the simplest strategy. Yellow- and blue-spotted salamanders, eastern American toads, northern ringneck snakes and eastern smooth green snakes go underground-below the frost line-in small animal burrows and caves. Blue-spotted salamanders can migrate across large expanses of ice and snow to enter their frigid breeding ponds in the spring. Northern redbelly snakes (slug eaters) are often found overwintering in ant mounds. The rarer four-toed salamanders, the northern dusky salamander, and the common eastern redback salamanders may remain in their summer homes, namely snags in marshes, logs and stumps in forests, and under ice-covered sphagnum moss.
Freeze-tolerance is used by northern spring peepers, gray tree frogs and wood frogs. They also seek protective shelters. In addition, through a series of biochemical and physiological changes, they may actually freeze during the winter. During this time, the heart stops beating, and glucose or glycerol in the body are used a antifreeze-gray tree frogs can even survive when they are -15_C! When the time comes, these frogs thaw out and start active living again. (There have already been reports of spring peepers calling this winter, misled by recent warm spells. Getting trapped out of hibernation can be fatal to herps; they cannot withstand direct exposure to frost.)
Some amphibians and reptiles seek winter homes under water. Some of these animals breathe through their skin, while others hold their breath. The skin-breathers are the red-spotted newt, northern two-lined salamander, bullfrog, green frog, mink frog, northern leopard frog and pickerel frog. These amphibians overwinter in ponds, lakes, streams and rivers. They need oxygen to survive, and they obtain it by diffusion though their skin;. Aquatically overwintering amphibians are like leaky boats-they are constantly filling up with water through the skin, and they use up most of their fat reserves (yes, even frogs have fat) to produce bucket loads of urine! In some ice-covered ponds and lakes, they may run out of oxygen before they run our of winter, they may freeze to death, or they may even get stuck in the ice. These situations result in winterkill. Turtles are extraordinary reptiles which can actual;y hold their breath during the winter. They rely on fat reserves, and use the minerals in their shell to control the acidity to the blood. (Runners and other athletes are familiar with the build-up of lactic acid that results from anaerobic respiration in the muscles during intense activity.) Turtles are capable of breathing through their skin, especially through the roof of the mouth. While less likely to experience winterkill, cases have been reported. All of the Maritime turtles (common snapping turtles, wood turtle, Blanding's turtle and eastern painted turtles) retire underwater.
Using neither purely terrestrial, nor aquatic, strategies, the two of Nova Scotia's snakes not previously mentioned-the Maritime garter snake and the northern ribbon snake-most likely overwinter in underground burrows, crevices and caves. However, the ribbon snake is very aquatic, and a relative of our garter snakes in Wisconsin has been found spending their winters at the bottom of abandoned farm wells.
Not all of the reptiles and amphibians remain behind to survive the weather. All three sea turtles *(Atlantic Ridley's, Atlantic loggerhead and Atlantic Leatherback), which feed along our coast in the summer, follow the warm currents to their breeding beaches in tropical waters.
Though they lack fur and the ability to produce their own body heat, amphibians and reptiles are well adapted to our winters.
*Stephen Friet is a research technician at the University of California, Berkley. He formerly studied frozen frogs at Dalhousie University, Halifax.
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