Frogs, turtles have right idea when it comes to cold
January 27, 2002

Winter is a serious time for 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 degrees, nor survive more than an hour at, say, 100 degrees. We are often asked, "What do they do in winter? How do they keep alive?"

Frogs and turtles hide and hibernate. Several species live in water 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".

"Shelly", the Woodland Dunes wood turtle, does the same thing her wild cousins do. She stays underground, in her "land habitat". Occasionally, she comes out of hiding and walks around. She even swims in her water-habitat for a while but returns to her hiding place. When out and about - she will not eat! She will be very hungry in March - maybe the singing robins get her going!

In times of summer drouth and intense heat, when ponds dry up, some frogs and turtles dig into the soil or creep under logs and rocks for protection from the burning sun and to conserve their body moisture. Then they, also, become torpid. This is called estivation. Turtles have been found as deep as 3 feet in mud under dry ponds - alive and well!

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. What do these animals do for oxygen when beneath the ice, often for months at a time? 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 heart beats 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.

In this "slowed state" frogs and turtles get oxygen from 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 skin.

Food is no problem for these winter sleepers. Apparently they require no more nourishment during a hundred days of torpor that they do during a day or two of normal activity in summer. Snapping turtles have been known to have as much fat on their bodies in early spring as in fall.

Turtles begin to bury themselves in the mud on the bottom of ponds, rivers and streams in September and early October. Occasionally, individuals may remain active all winter under the ice. Different species begin their "sleep" at different times - and also become active in spring, like frogs, at different times.

The winter, here in east central Wisconsin, has been mild - so far this year. There has been little snow. Maybe turtles, frogs - and robins - will appear a little earlier than usual!