Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [64]
Young painted turtle.
As already mentioned, map turtles hibernate in depressions of the river bottom where warm flowing water in the spring from the river drainage could reliably signal the arrival of spring. In contrast, painted and snapping turtles inhabiting small ponds hibernate under mud in shallow stagnant pools close to shore (Ultsch and Lee 1983) even though it is stressful for them in that nearly oxygen-free environment. Ultsch and co-workers (1985) suggest these latter turtles choose the shallow water of stagnant ponds to hibernate in because of some as yet unknown advantage. Perhaps, because such water would heat up rapidly in the spring, it could provide the turtles their emergence cue and thus reduce the length of hibernation. Turtles have a relatively short season in the north to recoup energy losses, mate, grow, and lay and mature eggs. However, hibernation in shallow water that might promote getting an early start in the spring has a large drawback; predators such as raccoons could reach them there. Turtles therefore probably choose the physiologically more stressful burial in the anoxic mud because that behavior would reduce predation, especially in fall and early spring when the turtles are sluggish.
The ability of a turtle to buffer its blood with potassium and calcium ions, to reduce the acidity of lactic acid, contributes greatly to its winter survival under the ice. However, somehow this solution doesn’t quite capture the whole reality of an amazing, astounding feat. It does not account for a turtle’s just plain toughness and tenacity.
Turtles, both painted and snapping, often get run over by cars on the country road where I live as they travel to and from their nest sites. One warm June day when I stopped to pick up what I thought was a dead washtub-sized roadkill snapping turtle, perhaps one I’d met earlier in happier circumstances, I was left to ponder what life or death might be to a turtle. A dozen or so Ping-Pong-ball-sized round eggs were strewn all around this smashed turtle. As I touched its tail, the animal retracted its legs. Thinking the badly smashed turtle might perhaps still be alive, although I knew it could never recover, I wanted to put it out of its misery quickly. I maneuvered my pickup truck to run it over squarely. Another car came by just then and the driver, quite understandably, stared at me angrily. But the good and difficult deed was soon done nevertheless, and I dropped the turtle off with my ravens after chopping off its head (since the body still twitched). To my great surprise the birds had still not fed from it by the next day. As I pulled once again on the tail of the long-since-headless turtle, her legs contracted into the shattered remains of shell, as they must have if the ravens had pecked it.
What is death to a turtle? what is being alive? For six months it stays under ice water, buried in mud, where all breathing, movement, and presumably almost all heart activity stops. In spring it comes up, warms up, takes a few breaths, and resumes life where it had left off. It has done so for the perhaps 200 million years or so that its kind have prospered with little change. After the nineteen-mile-diameter asteriod struck the Yucatan Peninsula in Central America 64 million years ago and raised a dust cloud that caused the “global winter” that killed off the dinosaurs, they continued to live on as superbly successful and diverse animals to the present time. Only now, subjected to ecological effects from humans, are some populations endangered. Otherwise, they are still so well designed that they require little change. Maybe they survived that fateful global winter after the asteroid struck