The Turtles of Winter
On a recent hike around Bass Lake, I spotted a turtle basking in the sun. The warmer weather must have drawn him out of brumation.
What, you may ask, is brumation?
Most all animals have adaptations that help them to survive the winter’s cold and lack of food. Some animals, like deer and beavers, stay alert and active. Many mammals, like groundhogs and black bears, will go into varying levels of hibernation.
Cold-blooded animals, such as our turtle, rely on their surrounding environment to keep them warm. When cold weather strikes, turtles go into a hibernation-type stated called “brumation.”
Some, though not all, turtles brumate under water.
At the sign of the first hard freeze of the season, that lovely basking turtle (I think it was a musky “Stinkpot” turtle) swam to the bottom of the lake, where it dug down into the soft mud. It was here that it first entered a state of suspended animation.
While in brumation, a turtle does not breathe in its conventional sense. Its heartbeat drops from 40 beats per minute to just 10. It will not eat. It drinks water only occasionally.
A good thing about being at the bottom of a lake is that the water down there, even if there is ice on the lake’s surface, will stabilize at 39 degrees Fahrenheit. This will keep the turtle in a dormant state, but not freeze it solid, which would kill it.
Also, colder water has a higher level of dissolved oxygen, which the turtle needs to “breathe” during its, sometimes, months underwater.
How does the turtle, which does not have gills, breathe underwater? The turtle can exchange gases through glands near its tail and throat. Oxygen is then entered directly into the blood stream.
Because the turtles are not moving or eating, after a few weeks in brumation, their body becomes full of deadly amounts of lactic acid toxins.
Our sly Stinkpot, however, has the ability to dissolve minute amounts of calcium from its shell. This calcium neutralizes the lactic acid.
This warmer weather can be dangerous for turtles and other reptiles. They emerge from brumation as the temperature rises (being cold-blooded, they have no choice).
With not much food to eat in winter, awake turtles can use up energy reserves and become weaker.
Snakes, salamanders, frogs and toads also enter a state of dormancy during the winter. Spring peeper frogs have the remarkable ability to be able to freeze solid. These creatures can literally turn into ice until the spring thaw.
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Amy Renfranz is an interpretive park guide on the Blue Ridge Parkway. She is a certified naturalist through the Yellowstone Institute and a certified environmental educator in the state of North Carolina. Her comments are made independently and do not reflect the views of the National Park Service.