Winter in the Great Lakes: Painted Turtle
The painted turtle (Chrysemys picta) is the most widely distributed turtle in North America, and two of the four subspecies, the midland painted turtle and the western painted turtle, live in the Great Lakes region. They prefer shallow, slow-moving bodies of water with soft bottoms and abundant aquatic vegetation. Painted turtles get their common name from the beautiful red and yellow markings along the head, body and shell. An adult painted turtle has a carapace (upper section of the shell) length anywhere from 4 to 10 inches. In the wild, they forage for aquatic plants, but will also eat small fishes, insects, spiders and snails.
Like all reptiles, painted turtles are ectothermic, or “cold-blooded,” meaning they rely on the outside environment to regulate their body temperature. Humans are “warm-blooded,” which means we can regulate our own body temperature by internal processes. We don’t have to worry about our body temperature changing much from 98.6 degrees, even on the coldest winter days. So how do painted turtles survive Great Lakes winters, when the days commonly average in the 20s and 30s? They take the ultimate “polar plunge.”
Painted turtles hunker down and hibernate underwater for the winter. They bury themselves in the mud, or in a muskrat burrow at the bottom of a shallow body of water (usually 1 to 7 feet deep). That’s right—air-breathing, “cold-blooded” animals bury themselves under near-freezing water for the winter. Hibernation can last from October to March, and luckily for painted turtles, millions of years of evolution have helped them to adapt for Great Lakes winters.
As the water temperature drops in autumn, temperate-climate turtles’ metabolisms slow. They stop eating. They become sluggish. They dig a hole and crawl in. Below 59 degrees, painted turtles’ body functions come to a near standstill. In this dormant state, the heart rate slows to only one beat every few minutes. Also, they do not breathe through their lungs. If conditions allow, they may absorb oxygen dissolved in the water through specialized skin cells near the tail. During hibernation in the Great Lakes region, a turtle’s body temperature averages 43 degrees, but thanks to physiological freeze tolerance, its skin, body and blood can be supercooled without actually freezing. At the end of winter, when the turtles emerge from the mud, they will have lived for several months in nearly freezing temperatures without air or food. Now that’s something to brag about!
You can see painted turtles at Shedd Aquarium and also meet one during one of our daily live animal encounters in the Local Waters gallery.
—Sam Bugg, Great Lakes public outreach manager
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