Other Outdoorsy Stuff

How Creatures Survive Winter

December 7, 2017

Photo: Ray Hennessy

When it comes to winter, we humans are wusses. We huddle in heated homes, drink hot cocoa, and buy cars with heated seats. If you want to talk winter, talk to the pros—the critters that run around outside without any of that stuff—and without clothes, for that matter outside. When the weather gets tough, the tough get going…in a variety of ways. Here’s how they make it.

Sleep It Off
When you feel the urge to stuff yourself with high-calorie meals, and snuggle into a blanket as the days get shorter, you’re feeling the mammalian urge to hibernate. For creatures that can lower their body temperature, hibernation and torpor are a reasonable way to deal with the demands of staying warm when there’s less food around to fuel their metabolic engine. Torpor is a short-term form of hibernation that’s driven more by food availability than shortening day length. Marmots and ground squirrels will hibernate, snoozing away the whole winter. Bears go through torpor, waking up periodically to hunt for a snack.

Get Fat
But to survive hibernation and torpor, critters have to fatten up. Even with a reduced body temperature, and often the shared heat of big groups, critters need to stock up on food to make it through the winter sleep. That’s why fall is such a feeding frenzy of bears feeding on salmon, squirrels stuffing their faces with nuts.

Photo: Bryan Minear

Be Large and Squat
A quick mental inventory of critters that live in the mountains or high latitudes shows that most of them are large and squat—bears, marmots, ground squirrels, muskox. They have large bodies to reduce surface area to size ratio, which means that they retain heat better. Long and gangly works in warmer climes, but when it’s cold, they lose too much heat. There are exceptions, like elk and moose, that are constantly on the move in search of food.

Be a Hyperactive Workaholic
And that’s the other solution: to be hyperkinetic, often beneath the snow. Pika, voles, and many small mammals stay active all winter. They’ll run around tunneling beneath the snow, where’s it’s surprisingly warmer than it is above and predators can’t see them. Pikas plan ahead, drying grass on the rocks in the summer and hiding the stash for winter. The metabolic demands of all this running around are huge, and these critters have to eat constantly.

Go Low
The easiest solution is to just drop down in elevation. There are many vertical migrants, from elk that migrate out of the Rockies into the lower elevations around Jackson Hole, to small birds like Varied Thrushes that spend the summers in the high country of the Pacific Northwest and winters on the coast. The strategy makes sense if you’re willing to make the trip, which has it’s own metabolic costs. And competition for food in the lowlands can be intense.

Go South
And if you’ve got wings, you can just head for the tropics. Many of our birds migrate for Central or South America, where they can skip the winter entirely. This is also a huge risk, with the metabolic costs of flying thousands of miles and the risks of getting lost, hit by a storm, or eaten along the way. But for birds, which don’t have the options of hibernation or torpor, it’s often the only option.

Photo: Josh Felise

Be Smart
When you look at the creatures that hang out all winter in the mountains or far north: polar bears, ravens, gray jays, coyotes, wolves: they all have one thing in common: cleverness. The pickings are lean, so the creatures that stick around have to be smart enough to find a variety of foods in a variety of ways. Winter tends to reward generalists: ravens can solve problems and are omnivores, fox, coyotes and wolves will take a variety of prey from voles to moose, and polar bears are famously clever in how they stalk seals on the arctic ice.

Go Solo or Teamwork?
Predators and omnivores who stick around all winter have a tough choice to make: go with a team or go it alone? Each strategy has its advantages. The solo hunters—coyotes, and wolverines—don’t have to share when they find food, which they make small snacks go farther to meeting their food needs. The team hunters—packs of wolves, flocks of gray jays and crows—have more eyes to spot potential food sources. They can team up to bring down larger prey that can feed the group, like a pack of wolves pulling down a deer or moose. Either way, winter predators are constantly on the move, looking food wherever they can find it.

Next time you’re huddled in your down parka in the snow for a few minutes before you duck back inside the warming hut, show some respect for the critters that are outside all winter.

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