Today’s Feb. 1 weather forecast advised that we were likely to experience a nearly 100 degree “feels like” temperature difference from the “Polar Vortex” mid-week wind chills of nearly 50 below zero to Sunday’s forecast showery high of above 50 degrees! That seems pretty extreme even by Iowa standards, but extremes like that shouldn’t surprise us. We live about as far as one can get in North America from the temperature-moderating influence of large oceans. We are at the mercy of competing air masses that often do battle right over us. Warm, wet tropical air confronts cool, dry northern continental air to produce summer super-cell thunderstorms, and frigid polar vortex air masses spin out of the Arctic to trigger winter blizzards. Life forms that survive here have an array of adaptions to get through the most stressful times.
We humans can pull on some extra clothes when it’s cold, or just stay inside, grab a warm cup of coffee and bump up the thermostat. The forecast weekend warmth will feel almost like shirt-sleeve weather after the recent deep cold, but would feel downright frigid if we encountered it in the summer. Even our human bodies can become better conditioned to uncomfortable temperatures, but it takes several days to do so. Our wild neighbors have fewer options. Some, like the thousands of geese so recently around our larger lakes, just leave when open water and food gets scarce. Others grow extra thick coats of fur or fluff up their down feathers, but when things get really nasty, they must find denser cover like cattail marshes or cedar thickets to survive. If they lack winter storm cover like that, some will die. Some mammals may hibernate to survive until spring, or just lay low for a few days until the extremes pass. Some birds and mammals, especially smaller ones, enter a kind of short-term hibernation called torpor that may last only a few hours or days. Creatures that don’t hibernate must find and eat more high energy foods to fuel their metabolic fires.
Only warm-blooded creatures can truly hibernate, a condition where they reduce their body temperature, heart rate and metabolic rate by varying degrees. Cold-blooded creatures like reptiles and insects cannot control their own temperature and enter a state of dormancy when it gets cold enough. Creatures like woodchucks and some ground squirrels sleep the entire winter away in their underground dens, with body temperatures hovering just above freezing and heart rates as low as one beat per minute. Bears, on the other hand, lower their body temperatures only a few degrees, but bring other body functions, like digestion, to a halt. Their kidneys continue to clear urea from their blood, but they do not urinate during their long naps. The urea is recycled into proteins that help to maintain muscle mass – a nice trick when the bear doesn’t drink any water for weeks or months to replace lost fluids. A female bear can even nurse her newborn young without drinking any water. She gets all she needs by metabolizing stored fat. Some hibernators, like bears and bats, may wake up, move around and even leave their shelters during brief winter warm spells. Too many or too long warm spells can be a problem for hibernators. Accelerated metabolism when not hibernating can deplete their stored fat too soon, leading to starvation before spring.
I sometimes wonder if I may be entering a state something like torpor when I sit down after supper, feel chilled and start dozing off. I suppose it might be a mental state known as stupor, too. I doubt if either one is actually giving me any survival advantage, but I know my wild neighbors must use every trick nature has to survive until spring.
Steve Lekwa is a former director of Story County Conservation.