How do animals survive the winter cold?

One can't help but wonder how the chickadee, a bird the size of a Tater Tot, doesn't freeze just as solid during the frigid winter months.

When the weather turns cold, animals - like people - can either adopt a strategy to deal with the change or flee to warmer temperatures elsewhere. Some, like groundhogs, simply choose not to deal with winter and sleep through the whole thing.

Limited resources and teamwork

Birds leverage every advantage they have to keep from freezing. They pump blood with faster heart rates and use their feathers to trap warm air against their skin.

"They've got a high body temperature, and they have to keep eating all the time in order to keep that temperature up," says H. David Bohlen, assistant curator of zoology at the Illinois State Museum. "And they keep out of the wind, hiding out in tree cavities."

Famed conservationist Aldo Leopold wrote that chickadees live by just a few rules: Stay out of the wind and never get wet before a blizzard.

Bohlen says some of the tiniest birds roost together and pool their small rations of body heat.

"When they roost, they roost so close together they are acting as one bird," he says. "Together, they have more body heat to keep from freezing to death."

Bluebirds have been known to pack into nest boxes, using the same principle.

Anyone who has ever constructed a snow cave can attest to snow's insulating properties.

"I had some redpolls one time that were roosting in some small spruce trees," Bohlen says. "And they were full of snow. The redpolls actually would get inside the snow."

Snowbirds

Migration is the movement of whole populations in search of food, not simply to escape the cold. If the snow covers the food supply of Canada geese, for example, the geese will move.

Consequently, mild winters mean geese migrate shorter distances - if at all.

The breeding range of dark-eyed juncos - those slate-gray and white birds under feeders right now - encompasses the northern U.S., including Alaska and Canada. They winter throughout the U.S. and northern Mexico.

Birds that rely on insects and nectar from flowers (like hummingbirds) have no choice but to move to southern climates, where their preferred food remains available.

Winter's positives and negatives

Normally, we think of cold weather as being a stress on wildlife, and that's true. It can be a challenge to find enough food. Even the hardiest critter can succumb when snow piles up, making it difficult to find food.

But sometimes it works in reverse.

In the Rocky Mountain West, a native beetle is wreaking havoc on trees because winter hasn't been severe enough to keep its numbers in check.

The mountain bark beetle has been killing pine trees, leaving mountainsides rusty brown, instead of green, in color. Municipalities are cutting dead trees as fast as possible because of the threat of fire. Real estate agents wonder how much property values will decline when homes with mountain views look out over dead and dying trees.

Reading the signs

Aside from large, conspicuous birds, such as bald eagles, it's not always so easy to observe how wild animals are doing.

To figure out how animals are making a living in the wild, we have to look for the signs left for us.

The pileated woodpecker seems to be doing just fine.

The pileated is a dramatic black, white and red bird the size of a crow. Its powerful bill tears into dead wood and strips bark from decaying trees.

A dead cedar tree in Starved Rock State Park in northern Illinois has fresh, oval-shaped holes drilled in it that are cut so neatly a carpenter would be proud of the work.

Cedar chips, fine as mulch, cover the ground near the trunk. Inside, the woodpeckers must have found a storehouse of insect eggs, pupae or other treats.

A bit farther down the trail, someone emptied a cache of acorns and feasted. There is nothing left but husks and shells. Sometimes it's hard to tell who has been at work. Other times, it's easier.

Raccoons travel at night but leave footprints, especially in the snow. Tracks provide a clue to their nocturnal ramblings. One print inside that of a hiker's boot is symbolic that we don't exactly own the trails we use.

Energy conservation

People like to argue about the merits of energy conservation. But for wildlife, conservation is a matter of survival.

During the colder months, wild animals are burning through energy like crazy just to stay warm, and every bit used must be replaced.

That's one reason wildlife experts ask bald eagle watchers not to flush eagles from perches if possible. Every time an eagle takes to the air, it's burning precious energy.

Animals that hibernate try to store up enough energy to get them through the winter months. But that's no easy task, even when critters like groundhogs slow their bodily functions and drop their temperatures to just above freezing.

Hibernation continues to mystify scientists. For one, animals that truly hibernate don't stay at extremely low temperatures. Every so often they spike up to normal temperature for a few days and then step back down again.

Joseph Merritt, senior mammalogist with the Illinois Natural History Survey, says it is thought that the immune system can't function properly unless it is at normal temperature.

"It's kind of crazy," Merritt says.

Ground squirrels, including groundhogs, are among the few true hibernators. Other mammals, such as the Eastern chipmunk and fox and gray squirrels, have periods of torpor during which they drop their body temperature into the 60s. But when the weather warms, they become active.

Mice experience stretches of torpor, just like chipmunks.

"They drop down, but then on nice days when the temperatures are up, you will see tracks on the snow," Merritt says.

"Shrews, on the other hand, don't have a clue," he says. "They don't drop their body temperature."

Instead, they forage for food nearly around the clock, mostly searching for insects below ground.

"There is plenty of insect food below ground," Merritt says. Shrews hunt via underground runways.

Voles are busy, too.

"They are herbivores - it is tough for them, but they are active," he says.

Franklin's ground squirrels, by contrast, are "hard-core" hibernators. They head for hibernation right after the breeding season, staying inactive from late August or early September through mid-April.

"This is pretty tough on them," he says.

Groundhog Day

When Punxsutawney Phil was extracted from his pet carrier on Feb. 2 to make his annual prediction about the weather, he was awakened much earlier than his wild brothers and sisters.

No self-respecting groundhog with any hope of survival would be rousing from hibernation in early February. For one, groundhogs need to eat right away to replace fat lost during hibernation. With no green plants available, Phil would be in real trouble.

"That's a bunch of nonsense on Feb. 2," Merritt says. "Groundhog Day is to hibernation what the tooth fairy is to dentistry."

State Journal-Register

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