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Coping with Winter: How Boundary Waters Animals Survive the Cold by Steve Volkening

While you are home warm and comfortable, planning your next canoe trip to the BWCA or Quetico, think for a moment about the animals you saw last summer. How do they cope with the long and frigid winter?

The Canoe Country is part of the boreal forest ecosystem which stretches across the northern US, Canada, Scandinavia and Russia. It is characterized by long, cold sunny, and relatively dry winters. The average January temperature in Minnesota is 10 degrees F, although it can drop to -60 degrees F. There are 110 inches of snow, compared to around 25 inches of rain the rest of the year. Snow frequently covers the ground from November until early May.

Because of the low temperatures, the snow remains light and fluffy, making it good insulation. Whereas temperatures at ground level may be well below zero, it rarely drops below 32 degrees F ten inches below the surface. Small mammals such as voles, deer mice, and shrews live in a maze or tunnels under the snow in relative comfort.

Many animals of the northern boreal forests have made amazing physical and behavioral adaptations to survive. Some are able to shut down the blood supply and reduce the temperature in their feet and ears. These smaller and exposed body extremities are more difficult to insulate and maintain at the same temperature as their body core. By lowering the blood supply, they keep them just above freezing. Other animals have actually developed methods to survive freezing solid!

Here is how some of the common animal residents of the Boundary Waters and Quetico cope with the rigors of winter:


Many people have heard that bears hibernate. Actually, it should be said that they are dormant rather than truly hibernating. Their body temperature does drop and their metabolism is lowered, but not as sharply as other animals.

Canoe country bears go into a deep sleep from mid-November until mid-April. A female typically will find a den under a fallen tree, in a hole under a brush pile, or in a rock crevice. She needs a protected place because her cubs are born in January. Males are sometimes large enough that they would overheat in a den, so they simply sleep outside.

Bears feed ravenously in the fall to put on a layer of fat. Some gain 100 pounds and can lose up to 30% of their body weight during their long winter sleep.


At the first sign of winter, raccoon make a leaf-lined den in a hollow tree. They don't hibernate; their heartbeat, respiration, body temperature, and metabolism stay at the normal rate. They may sleep for several weeks during especially cold periods. During warm spells, they emerge from their den to search for food, such as acorns, and to mate.

During a tough winter, when it is unusually cold and food is scarce, a raccoon can lose up to 50% of its body weight. Up to half of the yearlings don't survive their first winter.

Porcupine continue on with their lives pretty much as usual. They don't hibernate. They spend the winter in treetops feeding on bark and twigs as they do during the rest of the year. On a cold night, they may climb down to the protection of an underground den.


Otters remain active all winter. They delight winter visitors with their playful antics as they slide down riverbanks on their belly. A thick layer of insulating fat protects them from the cold air and water. It is for good reason that Native Americans valued their pelt. Their thick coat has up to one million hairs per square inch.

During the summer, otters have a rather large range of 5-40 miles. They are constantly on the move in search of fish, small mammals, frogs, crayfish, and mollusks. During the winter, they stay near falls or rapids where moving water prevents the stream from freezing. There, they hunt for fish. They live in a den in the riverbank with one entrance below the waterline. Another entrance above the waterline permits air circulation. Their den is lined with leaves and grasses for added insulation. They sometimes also use an abandoned muskrat or beaver lodge.


White-tailed deer adjust their metabolic rate, home range, and food supply in the winter. During the longer summer days, deer have a higher metabolic rate to take advantage of higher quality and more abundant food supplies. During the shorter days of winter, they lower their metabolic rate and reduce their body temperature. They survive on lower quality food such as white cedar and mountain maple twigs. They need to eat 6-8 pounds of this reduced nutrition food.

Deer also reduce their home range in winter. They often stay in the shelter of a conifer grove, especially at night. Studies have shown that night temperatures in these groves are up to 60 degrees warmer than out in the open. A deer's heavier winter coat, with its hollow hairs, also provides needed insulation against the cold.

Deer also match their reproductive cycle to the change in the seasons. They mate in fall. During the early part of their pregnancy, which occurs during the worst of the winter, the fetus develops very slowly and requires very little from the female. During the last trimester, the spring thaw provides more and higher quality browse for the mother such as aspen, willow, and birch. The fetus then grows rapidly and is born after the snow melts.

There are between five and six thousand moose in Minnesota, most of them in the Boundary Waters region. During the summer, moose are fond of aquatic plants. They can be seen with their heads in the water feeding on submerged or partially submerged plants. In the winter, they live up to their name, ''twig eater'', in the Algonquin language. When the water freezes, they eat up to 50 pounds of the stems and twigs of willow, birch, mountain ash, and balsam fir each day.

Their winter coats of hollow hair keeps them warm in temperatures as low as -40 degree F. When temperatures reach 20 degrees, they seek out the shade. Even in the summer, they are bothered by the heat. At above 60 degrees, they keep cool in the swamps or by swimming in lakes.

To satisfy their winter need for salt, moose sometimes kneel down along the shoulder of the road and lick up the salt spread by snowplows. That is quite a road hazard to discover as you round a sharp corner!


The spruce grouse makes major physical and behavioral changes in order to cope with the harsh winter. The shorter days of fall trigger a hormonal change, which causes scale-like growths to form on their toes. These growths double the surface area of their feet and serve as ''snowshoes'' to enable them to walk across the snow.

Before the start of winter, remarkable changes occur within the grouse's digestive system. It doubles the size of its ceca, a pair of sacs between its large and small intestine filled with digestive bacteria. It also doubles the size of its muscular gizzard, to help it grind up its coarser winter diet. While in the spring and summer, the spruce grouse feeds on insects, mushrooms and leaves, its winter diet is restricted to needles of the jack pine and lodgepole pine.

The grouse also alters its eating pattern in the winter. It feeds quickly at sunrise and dusk to be less vulnerable to the Great Horned Owl, its main predator. It rapidly fills its crop with pine needles and then retreats to the safety of a conifer bough, where it conserves its energy and digests its meal.

Grouse also understand the insulating properties of snow. They are known to fly headfirst into a fluffy snow bank. There, it stays relatively warmer than the frigid temperatures above ground and uses 45 percent less energy to produce body warmth. As spring approaches the female spruce grouse changes its diet again. The hen switches from pine to spruce needles. It needs calcium for eggshell production. Spruce needles contain three times as much calcium as pine.


Loons and eagles, the Boundary Waters two signature birds, don't have to adapt to the frozen winters of Canoe Country. Instead, they leave.

Loons require clear water in order to locate and capture the fish they feed on. Since they can't remain on the frozen lakes, they migrate south in late fall to the open water along the Atlantic and Gulf coasts. During the winter spent on the ocean, they eat rock cod, flounder, herring, and seat trout. Loons (and other sea birds) have a special gland behind their eyes. Salt from their ocean diet is excreted by this gland into the loon's nasal cavity, and then it drips off the bill. During this time at sea, loons are quiet. They make none of the yodels, wails or tremolos which so delight the many loon lovers.

The increase in daylight as spring approaches stimulates the loon's metabolism and tells them that it is time to return to the northern lakes. Not all loons return. Juveniles remain along the coast for two or three full years. They keep their dull gray plumage during this time and don't obtain their beautiful black and white feathers until they become adults at age four.

Bald eagles also don't spend the winter Up North. With the coming of fall, they begin to move towards warmer regions. When the northern lakes freeze, ea gles are unable to find fish, which make up 56 per cent of their diet. The waterfowl that they feed on also migrate, so eagles fly south. Wintering eagles in Illinois, Iowa, and Missouri often congregate around rivers where locks and dams provide good hunting. There, the water remains open even when the rest of the river freezes. Fish injured going through the dam's turbines provide easy meals.

As they return north in the spring to nest in the Boundary Waters, Bald Eagles can fly as far as 200 miles in a day. Just like human visitors, they are anxious to get back Up North!


Reptiles and amphibians are cold-blooded, meaning that they can't generate their own body heat. That is why you often see a turtle sunning itself on a log along the bank.

As cold weather approaches, the Western Painted Turtle, the most commonly seen turtle, buries itself deep under the water in the mud. They have the amazing ability to survive being frozen solid! Glycerol, a natural antifreeze, is produced, which prevents their cell membranes from rupturing as they freeze.

The Wood Frog also uses glycerol to survive freezing. During the winter freeze, its heart and lungs shut down completely. When the spring sun warms it, the body thaws, and the frog simply hops away. The American Toad uses a different strategy. It finds a patch of soft dirt, (no easy task in the rocky woods) and begins to dig down below the frost line with its rear feet. In northern Minnesota, this can be six to seven feet below the ground.


Like many insects, mosquitoes have a short life span - only two or three months. Before they are killed by the frost in early fall, females lay their eggs in pools of water. As the snow and ice melts in spring, the sun incubates literally billions of mosquito eggs. These eggs hatch into larval wigglers. They live in this stage for about a week before turning into a pupal stage called tumblers. Depending upon the water temperature, they emerge in swarms of adults in about a week.

It is only the female which bites. She needs a meal of blood in order for her eggs to develop and start the next generation. Males feed on flower nectar.

When you return to the Boundary Waters this summer, pause for a moment to appreciate the amazing adaptive abilities of these winter residents. They survive the brutal winters without the benefits of polarguardfleece, thinsulate gloves, or down parkas. Perhaps you can share these stories with members of your group.

You can also impress your paddling partners around the campfire by dazzling them with the collective nouns for animals which live in or around water. Some of these are well known, but others are pretty obscure:

  • bed of clams
  • bale of turtles
  • swarm of eels
  • shoal of bass
  • bask of crocodiles
  • siege of herring
  • pod of whales
  • army of frogs
  • mess of mackerel
  • den of snakes
  • smack of jellyfish
  • nun of salmon
  • shiver of sharks
  • herd of seals
  • hover of trout


       --article courtesy of BoundaryWatersMagazine


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