By LESLIE BISHOP, guest columnist
As temperatures dip in the autumn and I am cozy in my home, I can’t help but wonder what animals do in the winter.
Some leave and head south for warmer climates, some stay and remain active all winter, and others retreat into hibernation. A recent encounter with a reptile baby piqued my curiosity.
Reptiles, often called cold-blooded, are ectotherms, which means they have no internal means to regulate body temperature. How do they survive the cold?
On a sunny fall afternoon, I found a hatchling snapping turtle in my driveway as she was heading toward the pond. About an inch long, the turtle’s shell was still soft and flexible.
Despite her size, she tried to appear ferocious by exhibiting the characteristic defensive pose of looking up and opening her mouth wide. I was not intimidated and gave the little hatchling a lift to the pond so that she would not get run over.
I set her down on some moss by the pond, and the first thing she did was stick her head in the water and drink. She repeated this several times before slipping into the muddy leaves along the pond edge.
Snapping turtle mothers emerge from their aquatic homes in ponds, marshes or rivers in early summer and search for a place to dig and lay their eggs. They then return to the water, where they remain the rest of the year. The young hatch between September and October and must find their way to a pond before being eaten by a predator, like a crow or raccoon.
Like other aquatic turtles, snappers survive the winter by going into a state of inactivity or hibernation (called brumation in reptiles). As temperatures drop, snapping turtles find places to hibernate in shallow water near shore: in muskrat burrows, under logs or woody debris, under banks or buried in the mud.
The choice of where to hibernate can mean life or death. The site must be protected from predators, because the turtles cannot defend themselves when in a dormant state.
Studies show that most snapping turtles return to the same hibernaculum year after year — what was a safe place last year is apt to be safe again this year.
During hibernation, a turtle’s metabolism slows down with a heart rate as slow as one beat per 10 minutes. For energy, hibernating turtles’ cells break down stored carbohydrates.
Once a pond freezes over, the turtles have no access to atmospheric oxygen. Snapping turtles can tolerate low-oxygen conditions during hibernation, yet they still absorb oxygen from the water as long as it is available. Scientists are still trying to figure out the mechanisms for oxygen uptake in hibernating snapping turtles. Some species of aquatic turtles absorb oxygen from the water through their skin during hibernation; for example, painted turtles can survive up to five months underwater without taking a breath.
When I saw the first ice forming along the edge of the pond this past weekend, I thought of the little snapper hatchling. In my review of the scientific literature, I did not find any data about how hatchlings survive their first winter under water. Where will she hibernate? Is her small body size helpful in low oxygen conditions? Will she survive the freezing and thawing of the pond, the foraging raccoons and the hungry crows?
There are many unanswered questions. And I wish her well.
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She can be reached through the newspaper at [email protected].
