Animals who can't come in from the cold

Nature has developed a variety of cool strategies for surviving winter

Twice this winter my furnace broke. One stretch without heat lasted 36 hours. Though no pipes froze before the problem was fixed, my routine, to say the least, slowed down. I was cold all the time.

Coincidentally - fortuitously - I had a copy of naturalist Bernd Heinrich's book, "Winter World: The Ingenuity of Animal Survival." Cocooned in blankets on the sofa, I read. I wouldn't say I hibernated. No bear or flying squirrel in me. And I didn't huddle with anyone like snow fleas, or enter icy, suspended animation like a tree frog. I just tried to be oblivious to the cold as if I were a snapping turtle, only buried in blankets, not mud at the bottom of a pond. (I also kept breathing.)

Talk about getting an author's point!

Come winter, cold in the wild is a constant, a fact of life for creatures large and small. Heinrich takes readers into this world with lyrical yet scientifically precise firsthand accounts of animals' day-to-day survival skills. He outlines the fascinating evolutionary innovations worked out by living creatures to conserve their heat.

From caterpillars in the dark Arctic, flying squirrels in the frozen woods of Maine, to tiny bacteria bombarded eons ago as ice-laden comets rained down on our planet, Heinrich returns again and again to a single question: How has animal behavior and physiology adapted to the demands of a cold, often bitterly cold, environment?

The answers vary. Some insects and frogs develop antifreeze in their veins. Some remain in near constant motion, like his beloved kinglet, a tiny olive-colored bird with a brilliant colored crown.

This bird's behavior is typical of species' energy conservation. Work, work, work, and then huddle seems to be their motto. They fly around in small flocks of two to four birds, "apparently in order to be able to huddle to preserve warmth when they stop foraging at the last possible moment," Heinrich says.

His curiosity, like a crackling fire under a Douglas fur during a snowstorm, generates fascinating insights and incredible facts. Acute scientific observations flit from his pages like sparks. For instance, "Polyphemus moth pupae in winter have three-way protection: tough shells (cocoons) that are impenetrable by most birds; a camouflage wrapping old dead leaves; biochemical protection to prevent death by freezing."

Heinrich is a professor of biology at the University of Vermont and noted author of "Mind of the Raven," "The Trees in My Forest," "Bumblebee Economics," and other works.

He divides his time between teaching in Vermont and roaming the forests of western Maine, not far from where he grew up when, at the age of 10, his parents moved from Germany.

Not surprisingly, the books of Jack London, "books about a world of rugged people and hardy animals at home in the frozen woods of the north," fired his young imagination and set him on a course characterized as a romance with winter.

During World War II, Heinrich's father, himself a young boy, was forced without warning or preparation to live for an extended period of time in the Black Forest. Rather than embittering him, the experience instilled a lasting curiosity about the struggle for survival, an interest he obviously passed on to his son.

In each of its 25 short, gently illustrated chapters (e.g, "Snow and the Subnivian Space," "Hibernating Squirrels - Heating up to Dream," "Of Bats and Butterflies and Cold Storage"), Heinrich's book examines a critical factor for all living species: If you expend more energy to find food or shelter than you conserve, over the course of a winter, you will die.

The role of snow depth takes on new meaning when considered from a vole's point of view. The deeper the better for these rat-like critters, because deep snow allows them to remain in icy tunnels, secure from foxes and owls above. Depth also increases the amount of bark on snow-covered saplings they can safely eat.

The temperature of a bat cave lends new meaning to the principle of positive energy conservation, or in my case, setting the thermostat. Even if it's not freezing outside, once the insects are gone, bats don't have any food source left. If their cave isn't cold enough to foster hibernation, they'll need to keep eating. And a bat not sleeping in winter is a bat not conserving energy. Ultimately, it will consume its body fat and starve to death.

This summer, I'll have the gas company overhaul my furnace. As they do, I plan to sit outside in the sun and reread "Winter World."

• Jim Bencivenga is on the Monitor's staff. For a transcript of a recent MonitorTalk with Bernd Heinrich, see our website.