Wild Wonders of Winter

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But science has since changed its notion of hibernation, which is now defined not in terms of temperature or sleep but simply as a seasonal reduction of metabolism to survive frigid weather and scant food. In that context, overwintering black bears — even though they stir often and may sometimes amble outside their dens on mild days — are among the planet’s champion hibernators.

Starting in late summer, a black bear stocks its winter pantry — its own body — by gorging on nuts, berries and other high-carb foods, gaining as much as 30 pounds a week. In fall, bulked to the max, the bear enters its den, curls up like a cat and begins its winter snooze.

Most hibernators, such as woodchucks and chipmunks, do conserve energy by dropping their body temperature to 40 degrees or lower. Even so, the little calorie-burning creatures must rouse themselves every few days, chow down on stored food, and excrete wastes before returning to a deep sleep. If they didn’t, they’d starve.

But for three months or more, a hibernating black bear — whether sleeping soundly or barely dozing — neither eats, drinks, exercises, urinates or does what bears are otherwise known to do in the woods. Its breathing slows, its heartbeat drops from 40 beats a minute to about 10, its oxygen intake is reduced by half — yet throughout the winter its internal furnace burns at a near-normal temperature of about 88 degrees, just 10 degrees lower than in the summer. It lives entirely off its body, breaking down fat cells to supply water and up to 4,000 calories a day, and recycling the urea it would normally excrete in urine to manufacture protein, essential for maintaining muscle and brain function.

So it is that a fully hibernating black bear, while taking in no energy whatsoever, can sustain itself in comfort all winter — and in the case of a pregnant female, can even give birth and keep her babies nourished and warm. In January, the expectant mother awakes long enough to deliver cubs, then returns to dormancy while the young snuggle against her warm body and nurse.

Dive! Fly! Dive!

With a boat for a body, oars for legs, a built-in scuba tank and wings that can propel it for five miles, a water boatman doesn’t let a little thing like winter slow it down. Water boatmen, which comprise more than 120 species of insects in temperate North America, are busy denizens of ponds, lakes, puddles and other languid bodies of water, even when those bodies are covered by ice. All a boatman needs is a pocket of air from which to periodically refill its breathing apparatus: a bubble trapped beneath its wings or spread over its upper body. With its oxygen supply renewed, the quarter- to half-inch-long bug can dive back down to resume foraging on algae and aquatic plants. Most species are mainly vegetarians, though several also prey on insect larvae.

It’s easy to see where the water boatman gets its name, given its broad oval body and rowing legs. It actually uses only the two pairs of flattened, hair-covered hind legs for swimming; its short spoonlike forelegs are useful for hanging onto underwater plants and for scooping algae and other microscopic organisms into its mouth.

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