by Bob Engel, Marlboro College Professor Emeritus of Biology and Environmental Science   

Photo credit: Peter Bergstrom

Have you ever been winter camping? No? Try it sometime; the experience will definitely result in more empathy for the wild things out there. All seasonally harsh environments result in just three kinds of adaptations in the local inhabitants: (1) escape, (2) retreat, and (3) tolerance.

Know people who go to Florida every year? Right, they escape. Wimps. But so do migratory birds, hibernating woodchucks, turtles in the mud, diapausing insects, and the seeds, bulbs, and belowground meristems of plants. There are really only a few things that strictly tolerate the winter: trees and shrubs, some larger birds, and big mammals like coyotes, deer, and moose. Almost everyone else employs some combination of tolerance and retreat. Think something like a red squirrel here. They're out foraging on a decent day, but stay holed up during really tough weather. Also, think chickadees.

I cherish these little birds. They're so peppy, curious, tolerant (of us), and clever. They're the only birds I actively feed. But they are also full of sneaky tricks to deal with the winter. To put things in perspective, their northern range goes all the way to Fairbanks, Alaska, where they now have about 3.5 hours of daylight to eat enough to survive a 21-hour, frigid night. So is Vermont the "banana belt" for them? Not quite.

The tolerance part of their game involves more winter feathers, avoidance of windy microclimates, stashing extra food (along with new nerve cells to help remember where the stuff was put), and adding about eight percent of their weight each day in fat.

The retreat part is, perhaps, even more interesting. Just as when they nest, they roost at night in tree hollows. There, they may avoid the worst weather, may leave some food, and may huddle with other chicks to share heat. But they also do something amazing with their body temperatures in those cavities--they lower them as much as twenty degrees F each night. Because heat loss is a function of body temperature minus ambient temperature, by lowering body temperature, a chick reduces the difference and thus consumes that stored fat more slowly. Short-term hibernation, called torpor, is a controlled, often nightly, hypothermia.

A famous study of a small rodent puts things in perspective. Pocket mice also enter torpor to make fat supplies last longer. If they enter torpor and go through a 10-hour night, they spend about 80% less energy than they would if they were forced to maintain their normal body temperatures. The mice even save energy if they enter torpor and are then immediately aroused (about a 50% savings for the three hours involved). As you might imagine, rewarming the cool body takes a large portion of the energy savings. In the mice, arousal takes about an hour and is about five times as expensive as spending an hour in torpor.

Okay, back to our chickadees. Imagine them, every night, in that relatively protected cavity, eight percent heavier (if they've been lucky), maybe huddling, and then letting their bodies get cooler and cooler. Then imagine the rather violent shivering of their flight muscles at dawn as the little group slowly rewarms to 108 degrees F and begins a new day.

In this season of cold and dark, there is still another lesson for us. Your house is just like that miraculous little bird. Let it go torpid every night. Get a programmable thermostat. Yes, I know, the furnace moans and groans in the morning, but just like the chickadee, your heat source didn't have to keep the house's body temperature elevated all night.