Painted turtle has interesting way of surviving winter
Winter arrived Friday and Monday is Christmas Eve. While we’ll be snug in our beds, anxiously waiting for Santa to arrive, the season of ice and snow can be quite different for wild animals, especially our region’s reptiles and amphibians.
I had not really thought about hibernating reptiles until I received an email from my friend Dick Waterman. He has a large pond adjacent to his property, created decades ago by the industrious work of a resident beaver family. When the ice forms solid enough on the pond for him to walk on, he’ll venture out on the ice to check several wood duck boxes he maintains for the colorful resident waterfowl.
“It was wood duck box inspection time today. Even for someone with a lot of experience, an inch or so of black ice that is so clear one gets the sense of walking on water, can be unnerving, particularly when the ice makes cracking sounds under your weight. But it is work that needs to be done, and who knows when the next safe ice will occur? Walking a shallow pond with black ice affords a view of the bottom if the sun is brightly shining, which it was. I saw a couple of schools of shiners and, to my surprise, a painted turtle.”
What was that painted turtle doing swimming under the ice and how does it survive the winter when the water is frozen? I did some research and discovered some secrets of the painted turtle to share with you.
Painted turtles are cold-blooded animals (ectotherms) with their body temperature and metabolism determined by external temperatures. When it’s cold their metabolism slows down.
Painted turtles spend most of their time in ponds and slow-moving fresh water, and, as Waterman witnessed, a sheet of ice doesn’t stop them. Here in New England, and the northern parts of the painted turtle range, the adults head for deeper water and winter under ice buried down in the mud beneath the water.
All turtles have lungs, and during warm months they get most or all their oxygen by breathing air. While submerged for the winter, the painted turtle can absorb some oxygen through its skin, mouth and cloaca. The cloacal opening is the anus. During winter months, when the turtle’s body functions slow down, the cloacal widens to allow water to circulate into the opening. Like gills of a fish, the circulating water provides oxygen that is absorbed by many capillaries in the cloacal opening.
Painted turtles can hibernate for months at low oxygen levels (hypoxic) and even no oxygen (anoxic) environments. For most vertebrates the heart and nervous systems fails without oxygen, making the painted turtles’ hibernation somewhat amazing.
Painted turtles reduce their metabolic rate by as much as 95 percent with access to oxygen and as much as 99 percent when there is no oxygen available. This low metabolic rate prevents them from being active but also reduces their energetic needs to a bare minimum, allowing them to survive without food or oxygen.
Most hibernating animals, such as bears and woodchucks, rely on excess fat in their bodies to get them through their winter dormancy. These fat stores can only be used when oxygen is plentiful.
To survive without oxygen, painted turtles break down glycogen, the predominate storage form of glucose and carbohydrates. This process releases enough energy to keep them alive but also creates lactic acid, which can build up enough to be deadly (acidosis). The amazing painted turtle will dissolve small amounts of calcium from their shells into their bloodstream to keep their hearts beating properly and buffer the production of lactic acid.
The next time I venture out on the ice of one of our local ponds, I’ll be thinking of the amazing painted turtles snug in the mud down below the surface. Their ability to survive the winter is one of the more interesting characteristics of these amazing animals.
Winter has arrived, and the season of snow and ice is upon the land and waterways. Most of our wildlife will remain active, seeking food and shelter among trees, fields and forests. Some are in a hibernating state within burrows or, like the amazing painted turtle, buried in the mud below frozen ponds and lakes.
We live in a beautiful region full of unique and interesting flora and fauna. I hope you will join us as we care for, enjoy, and pass on to the next generation this place we call home – The Last Green Valley.
Sources for the column include “Cool Green Science,” a conservation blog of The Nature Conservancy, and “Stokes Nature Guide to Amphibians and Reptiles” by Thomas F. Tyning
Bill Reid is chief ranger of The Last Green Valley National Heritage Corridor and has lived in the region for more than 35 years. He can be reached at email@example.com.
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