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Making it in Montana’s winter

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Trumpeter swans are among several waterfowl species that have adapted to endure the Montana winter. NPS PHOTO

How animals survive

By Bruce Auchly MONTANA FISH, WILDLIFE AND PARKS

Animals of Montana have long prepared for winter. Those still here, that is those that did not migrate, are either asleep or hunkering down for the long winter.

Asleep means hibernation, both real—think marmots and bats—and those that simply enter a deep sleep but technically do not hibernate, bears for example. True hibernators lower their body temperature and respiration rates. Bears, while not truly hibernating, are curled up, insulated by fur, fat and snow depth from the ravages of winter. They can and occasionally do wake up briefly, but they will generally sleep for months.

Deer, elk and antelope stay awake and survive winter through four main adaptations: an insulated coat, reducing their metabolism by as much as one-third of what they need to meet basic life functions, remaining bedded for long periods during bad weather and relying on stored body fat.

Up to 30 percent of a deer’s winter energy requirements can be met through body fat. By the way, don’t believe the old hunter’s tale of predicting a winter’s severity by the amount of body fat on a deer or elk. The amount of fat says more about the animal’s ability to find adequate food in the late summer and fall than the upcoming winter.

Birds that survive a Montana winter require special equipment. Waterfowl, like geese and ducks, will stand or sit for hours on an ice shelf next to a river’s open water to better see and escape predators. They survive by wearing a nice, plump down coat. Their exposed feet have adapted, too.

First, their legs and feet have very little muscular, or soft, tissue that needs blood to keep warm. The few muscles that operate the foot are mostly higher up in the feather-covered leg and connected to the bones of the feet with long tendons.

Second, warm blood flowing through the birds’ arteries passes close to cold venous blood returning from the feet. As arterial blood warms up the venous blood the few tissues in the feet receive just enough warmth to avoid frostbite.

All birds have feathers that create air pockets between the feathers and the skin that help contain heat. And many have behavioral techniques to survive. Some cluster together. Others will roost in tree cavities, dense foliage or brush piles to cut both the wind and heat loss. Grouse will bury themselves in snow. Depending on the species, some birds can even shiver specific muscles to increase metabolism and generate extra heat.

Animals that spend their winters in Montana have evolved some amazing strategies to survive. We should be so lucky.

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july, 2020

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