How they survive Canadian winters remains a mystery
by Bob Bancroft
Turtles capture my imagination and curiosity whenever I encounter them in North America. With their “ET” gaze and simultaneously prehistoric-futuristic appearance, turtles are cool. Kids might be surprised to learn that real turtles have survival abilities that rival their sewer-dwelling, pizza-chomping cartoon counterparts.
Some First Nation tribes in North America considered the world to be an island that was being carried on the back of a great turtle.
Painted turtles, Chrysemys picta, have a sleek, smooth, pancake-sized “hardtop” called a carapace. Their exposed body parts are adorned with intricate patterns of red, yellow, olive and black. The belly armour of Eastern painted turtles, called the plastron, has a solid yellow colour. They contract their limbs and head into that shell to avoid danger.
Poet Ogden Nash pin-pointed a feature of turtle shells:
The turtle lives ’twixt plated decks
Which practically conceal its sex.
I think it clever of the turtle
In such a fix to be so fertile.
Painted turtles are members of an ancient turtle tribe that managed to outlive the dinosaurs, but many populations are now in decline. Existing across southern Canada from coast to coast, painted turtles are North America’s most widespread, shelled reptile. Look for them in ponds, along lakeshores, in the backwaters of streams and rivers, and in marshes. They favour aquatic environments with still waters, plenty of aquatic weeds and soft, muddy bottoms.
A typical painted turtle summer day begins with breakfast. Adult painted turtles dine on just about anything—plant or animal, dead or alive. They catch fish and aquatic insects, larvae or nymphs, snails and other invertebrates that make up their menu. Youngsters prefer animal material, consuming more vegetation, such as pieces of water lily pads, as they become older. These turtles dive down as deep as two metres when feeding and may stay submerged for almost an hour.
After feeding, they often engage in a mid-morning sunbath. Since they are coldblooded, they must use the sun’s warmth to keep active through the entire open water season. They climb out on favourite rocks or logs that are exposed to the sun at various times of the day. I often see them in groups along the quiet stream where we canoe in New Brunswick. With necks and legs outstretched, and toes spread wide, they become silent solar collectors until their bodies reach temperatures of about 21.4°C.
They may not feed again until the evening. At night they sleep underwater, rising to the surface briefly when they need to breathe.
It takes four to six years for a painted turtle to become an adult. Females are larger. Males have more elongated fore-claws and longer, thicker tails. The breeding season begins in the spring, with a brief courtship and mating ritual. A male will swim backward in front of the female, caressing her face with his toothpick nails during courtship. If she is interested, she responds by tapping his outstretched limbs with her own stubby nails.
When ready to lay eggs, females clamber on to dry land in June and early July, to find gravel or sand beaches, roadsides and even cultivated fields. There she digs a nest and lays four to 11 or more oblong eggs. She covers the eggs and hole with earth that she packs down securely. Females will spread a few twigs or grasses over the surface in an effort to conceal the nest. Sun and the heat of the soil will incubate the eggs for months.
But egg predation is a serious issue, with up to 90 per cent of the nests lost to predators. Raccoons are the main culprits, but skunks, chipmunks, woodchucks, gray squirrels, foxes, garter snakes and humans also destroy some nests. Severe flooding can produce the same calamity.
Hatchlings from nests that survive claw their way to the surface during the period from late September to the end of October. Those leaving the nest are vulnerable to predators that include muskrats, mink, raccoons, snapping turtles, bullfrogs, large fish, great blue herons, crows, gulls and water bugs. Only about one in five eventually survives to become an adult.
Raccoons, bald eagles and ospreys may also take adults. But humans with their automobiles, habitat destruction, pesticides, rifles and the pet trade are responsible for the annual death of most painted turtles.
Their reaction to predators is sometimes passive, but many attempt to escape by kicking and scratching, peeing on you and occasionally biting.
If the autumn arrives as a chilly one, and the surface temperature of the upper part of the nest becomes cooler than the bottom temperature, the newly-hatched turtles will overwinter in the nest, and eventually dig their way out the following spring. This ability is remarkable, because the nest and the young turtles freeze. Painted turtles are the only reptiles known to be able to survive with up to 65 per cent of their total body water frozen. Their hearts, blood flow and breathing stop—and somehow restart in the spring.
Adults hibernate by submerging themselves into pond bottom ooze in the fall, burrowing deep enough to avoid freezing temperatures. How they manage to survive over the winter this way is an unsolved mystery. Scientists know that they can breathe oxygen through their skin while submerged, but being encased in mud offers little option for acquiring oxygen.
Estimates of how long a painted turtle can live range up to 40 years, making them long-term neighbours in our New Brunswick property. Their habitat there is a lovely stream surrounded by a floodplain forest that has been managed by beavers for centuries. The multiple dams and houses the beavers create each spring after the Saint John River floodwater subsides provide a sufficient amount of deep, quiet water suitable for predator protection and the growth of many aquatic plants.
Paddling along there, the plops sounding ahead on the water give away the painted turtles that one doesn’t see. A snapping turtle shows annually when she lays her eggs on the roadside near the highway bridge. And it’s a safe bet that the wood turtles lay their eggs every year in disturbed sections of the floodplain. It’s a turtle heaven. We are happy to keep it that way.