WHERE DO TURTLES GO IN THE WINTER?

by Whit Gibbons


March 11, 2007


Global climate change could potentially turn late winter into early spring, but winter is officially here for several more days, until the spring equinox on March 21. So, a question from Florida still qualifies as a wintertime question.

Q. Where do turtles go when it's cold? I just read an article about someone in Brandon, Fla., who brought their pet baby turtles inside and put them in the bathtub to protect them during a cold snap. The story focused on the pet golden retriever that ate one of the turtles and was taken to the vet. I don't actually care what happens to turtles eaten by dogs but want to know if cold is really a problem for turtles in the wild--freshwater turtles, sea turtles, tortoises?

A. Cold is not a "problem" under natural conditions for native animals or plants. Individuals unable to tolerate seasonal changes in temperature under natural conditions are typically eliminated through natural selection. Thus, the genetic makeup of future populations is determined by the survivors, individuals who could withstand a cold climate. Ancestors of all turtles on earth today survived whatever natural conditions of cold they were confronted with. But what do they do when no one is around to put them in a bathtub for the dog to eat?

Every species living in the temperate zone deals with winter's cold. Birds fly south as winter approaches. Mammals add a layer of body fat when cold weather arrives. Trees lose their leaves before they freeze. Turtles, likewise, have their own special ways of dealing with winter.

What happened to the turtles you saw basking on logs or rocks in the sun during spring, summer, and fall, that then disappeared when it got cold? At body temperatures of about 40 to 50 degrees F, most reptiles become sluggish, stop eating, and seek hiding places to get safely through the winter. But turtles are air-breathing animals with lungs, so can they live out the winter underwater?

Many aquatic turtles go into the mud or under the bank where the water is cold but does not freeze. An advantage most reptiles have over many mammals and birds is that their metabolism drops with their body temperature, meaning that they require less oxygen. Some turtles can stay underwater for days without taking a breath, as long as the water stays cold. Many species actually absorb oxygen from the water through tissues in the throat and tail.

Most of the world's tortoises live in warm climates, but the gopher tortoises of the Southeast have an unusual strategy for escaping cold winters. They retreat into underground burrows that serve as natural caves for protection from cold and predators. Gopher tortoises dig the burrows, which are often more than 20 feet long. In South Carolina, Georgia, and northern Florida, gopher tortoises may stay underground for days or weeks at a time until warm weather returns.

Most sea turtles have a different approach to dealing with winter. They simply do not live where it is cold. Loggerhead and green sea turtles commonly lay their eggs on beaches of Florida and even into Georgia and the Carolinas, but this is characteristically in the early summer. And hatchling sea turtles normally crawl to the sea in late summer, before the Atlantic waters of the Southeast become frigid. So, most sea turtles spend time in the temperate zones only during the warm seasons.

As always in biology, we can expect an exception. The world's largest turtle, the leatherback, nests in the tropics but actually travels into the Arctic Ocean during the summer. According to Jim Spotila's book, Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation (Johns Hopkins University Press, 2004), the giant leatherback sea turtles use a variety of mechanisms to stay warm even in icy waters. These include, a thick layer of body fat for insulation, blood vessels in their fins that replace cold blood with warmer blood, and a big body that loses heat slowly.

Incidentally, I checked into the Florida "dog eats turtle" story. Worry not. Both dog and turtle are safe after a little operation at the vet's. Both are probably hoping Florida doesn't have any more cold snaps this year.



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