By Stacey Venzel
Similar to other reptiles, turtles are cold-blooded. While this means their body temperature changes with the environment, turtles can still survive the winter.
Found in almost every part of the globe, some turtles can tolerate temperatures below freezing. Their bodies adapt to the cold via hibernation, insulation, large body size, blood circulation or antifreeze production.
While mammals hibernate in the winter, reptiles enter into a state of brumation. In cold temperatures, turtles can lower their heart rate and metabolism, thereby conserving energy and warmth. Aquatic turtles will brumate in deeper parts of ponds where the water will not freeze.
Oftentimes, turtles that hibernate will also pad themselves against the cold by burying in layers of the earth. Burrows of gopher tortoises are up to 20 feet below the ground surface where temperatures do not reach freezing. Box turtles bury themselves under leaves and soil to stay warm.
LARGE BODY SIZE
Children tend to bundle up more than adults in the winter because they get cold quicker. Similarly, large turtles use their size to stay warm. This form of conserving heat is called gigantothermy (sometimes called ectothermic homeothermy or inertial homeothermy), in which having a bigger body allows the individual to conserve more heat. Adult leatherbacks are so large that their internal body parts have a lot more buffering from surface heat loss than green sea turtles that do not even grow to half the size of leatherbacks.
Additionally, leatherback sea turtles have been seen swimming among chunks of ice as far away as the subarctic waters of Alaska, Nova Scotia and Russia—the furthest north of any reptile. They use a method of restricted circulation, which funnels all the blood to their core to keep their vital organs warm. This also allows them to dive down to frigid oceanic depths of 3,000 feet.
Frogs and fish have been known to produce antifreeze and some turtles can, too. Painted turtle hatchlings make a chemical that keeps their blood from turning into crystals during freezing temperatures.
WHAT IS TOO COLD?
Turtles have not been found living in Antarctica, but they do survive subfreezing temperatures, inhabiting all six other continents and every ocean. However, excessive cold can be fatal to turtles. Massive “cold stunned” sea turtle stranding events occur every few years around the globe when the ocean temperature drops to extremes for long periods of time.
Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 299.
Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 20, 26.
Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 28, 44, 92.
Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 6-7, 47-49.