Forest Preserve District of Cook County, Illinois
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Hibernation of Frogs and Turtles
Nature Bulletin No. 485   March 16, 1957
Forest Preserve District of Cook County
Daniel Ryan, President
Roberts Mann, Conservation Editor
David H. Thompson, Senior Naturalist

Winter is a serious problem in the world of frogs and turtles. So is a very hot dry summer, Like snakes, these cold-blooded animals have little or no ability to keep warmer or cooler than their surroundings; their body temperatures rise and fall with those of the places where they are. Few, if any, can endure long exposure to more than a degree or two below 32 F, nor survive more than an hour at, say, 100 F. We are often asked, "What do they do in winter? How do they keep alive?.

They hide and hibernate. Those that live in water hide away beneath the ice of lakes, ponds and streams; those that live on land burrow under leaf litter and soil below the frost line. They become very sluggish and torpid. They do not eat and all life processes drop to a very low ebb. They "sleep".

In times of summer drought and intense heat, when ponds dry up, some kinds of frogs and turtles dig in the soil or creep under logs and rocks for protection from the burning sun and to conserve their body moisture. Then they, too, become torpid. This is called estivation. During the extreme drought of 1934, while deepening a pond which had gone dry, one of our senior naturalists found a large snapping turtle beneath three feet of soft earth but alive.

All frogs and turtles breathe with lungs, at least from spring until late autumn, just like people. We can see them inhale and exhale when basking in the sun -- faster on warm days, slower when it is cool. You may wonder what they do for oxygen when imprisoned beneath the ice, often for months at a time. The answer is that their bodily fire, called metabolism, burns lower and lower as winter sets in, until it is literally reduced to a mere spark of life. Their hearts beat at long intervals and they crawl or swim, if at all, in slow motion. Very little oxygen is needed but that little is a matter of life or death. They get it from oxygen dissolved in the water: not like fish, through gills, but, in the case of turtles, through the linings of their mouths and throats; or perhaps, as in the case of frogs, through their skins.

The necessity for that oxygen dissolved in water was strikingly shown at our McGinnis Slough in the winter of 1944-45 when there was a thick layer of ice covered with snow from early December until mid- March. Tens of tons of fish died from suffocation and so did hundreds of turtles and frogs. When the ice finally melted away, some painted, Blanding's and snapping turtles washed ashore and recovered but many were dead or so weakened that they died after reaching the surface .

Food is no problem for these winter sleepers. Apparently they require no more nourishment during a hundred days of torpor than they do during a day or two of normal activity in summer. Snappers caught in spring and butchered for eating, seem to have almost as much fat as those captured in fall.

In autumn, most Illinois turtles bury themselves in the bottom mud of streams and bodies of water, or crawl into the submerged entrances of muskrat burrows, or hide under sunken logs. The snappers, softshells and stinkpots usually hole up in October. Later, the sliders and painted turtles retire. The map turtles, and occasional individuals of other kinds, are somewhat active all winter. In Illinois, only the box turtles hibernate regularly on land -- burrowing deeper and deeper in soft soil as the nights become colder.

Last April, under about two inches of bare soil near the Little Red Schoolhouse nature center, we dug up two baby painted turtles still alive and partly inside the shells of their eggs laid the previous summer.

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