Wild animals endure many hardships in order to survive, but the most challenging of these is winter. Cold temperatures, wind, lack of cover and little food make life during the winter months difficult, but Michigan's wildlife species have adapted different strategies to survive and sometimes make winter almost seem bearable.

To escape winter's bite, many summer resident birds migrate, but this is a costly strategy. It requires a large amount of energy to make the journey. Migratory birds also are more vulnerable to predation during long migratory flights.

Although several species of bats travel south to hibernate, some bats actually travel north. Many of the abandoned mines in the Upper Peninsula provide stable, moist climates for bat hibernation. Millions of bats save themselves a long trip by adapting to these man-made structures. Bats also are infamous for crawling into heated buildings and hiding, waking up once each month.

Perhaps the most interesting migratory flight is conducted by the Monarch butterfly, which travels to Southern California or highlands in northern Mexico. This is a one-way trip for the adults. After over-wintering these butterflies will mate and lay eggs, ensuring the return to Michigan is made by the next generation.

Migration, however, is not always a long-distance affair. When deep snows pile up in the Lake Superior watershed, white-tailed deer travel south to wintering yards. These low-lying areas have a dense cover of white cedar. With snow depths and winter winds decreased inside these yards, deer take a sit-and-wait attitude, reducing activity levels and energy demand, while depleting the local food supply and their store of body fat. If winter is short and mild, most survive; if it is long and cold, many can starve.

Some birds actually find Michigan a pleasant winter oasis. The great gray owl will migrate south into the forests of northern Michigan, and snow buntings which nest on the tundra of northern Canada find the dunes and open crop fields of southern Michigan quite balmy and will spend the winter foraging in these areas.

There are only a few Michigan animals that practice true hibernation. Woodchucks, bats, some mice and ground squirrels are Michigan's true hibernators. In fall, woodchucks gain another 30% of their summer weight, line an underground cavity with grass and leaves and plug the entrances before curling up in a ball. The animal's heartbeat drops from 100 to four beats a minute and its body temperature drops from 98 to about 40 degrees. When they emerge in the spring they will have lost half their fall weight.

A more common strategy is dormancy or torpor. This occurs when an animal enters a state of reduced metabolic activity, sleeps for a long time, wakes up, moves around a bit and goes back to sleep. The duration of sleep and activity often varies dependent on the severity of the weather.

Most mammals feed heavily in the fall putting on a layer of fat that supplements the meager food that is available during the winter. Opossums will den in hollow trees or burrows and may even share their winter quarters with rabbits, skunks, raccoons or woodchucks.

Black bears enter a form of dormancy that is more like lethargy. Females give birth to their cubs during the winter denning period; in true hibernation this would not be possible. In their sleep state both the heart rate and body temperature decline and their digestive activity stops. However, if disturbed, bears can rouse readily, much to the consternation of biologists conducting bear den studies.

Cold-blooded animals, like amphibians and reptiles seek sheltered places. Crayfish chimneys offer safe wintering sites to snakes, frogs or salamanders and often at the same time. Many frogs dive to the bottom of lakes or ponds where they burrow into the mud to wait until spring. Some snakes gather in large numbers, "ball-up" and hibernate together to stay warm.

Some insects survive by spending the winter as larvae, while others over-winter as adults in large, tightly clustered colonies. Other insects have the ability to produce glycol in their blood, which acts as an anti-freeze. They then enter a state of suspended animation.

But most animals can't migrate or sleep through winter, so, to help them adapt, most mammals increase the length of guard hairs and the amount of underfur to increase the insulating value of their coats. The winter hairs of the white-tailed deer are hollow providing an extra layer of insulating air. Aquatic mammals, such as otter and mink, grow thick layers of insulating fat and have specialized glands that produce a water proofing oil they comb into their fur. Beavers, in addition to using their water resistant oil, store fat in their tails and cache food under the water.

The adaptations of some animals help them move around more easily during winter. The large feet of snowshoe hare and lynx help them stay on top of the snow, and ruffed grouse grow fringes on the edges of their toes that act like snowshoes. Staying on top reduces the amount of energy needed to move around.

Ruffed grouse also practice snow-roosting. When the snow gets deep, grouse burrow, or more dramatically plunge into snow from flight. Once down inside, the grouse creates a cave. The bird's body heat is trapped inside making the cave a cozy place to stay. If snow cover is lacking grouse will roost in thick conifers to stay warm.

Ducks, geese and swans have feathers and oil glands that keep water away from the skin. The blood vessels in their feet are so close together that warm arterial blood flowing from the body heats the cold blood in veins of their feet. Song birds adjust their internal temperature to reduce heat loss. They also fluff their feathers to increase the air space for insulation and they shiver to create body heat.

Predators like bobcats, fox and coyote are active all winter, often increasing their range to secure food. Their hearing allows them to detect small rodents moving underneath the snow. Wolves do not seem to find winter a significant hardship, but, in deep winter, they may linger closer to a deer yard, where they can hunt young or weakened deer.

Moose in Michigan's Upper Peninsula are designed for winter. Their long legs allow them to move easily through deep snow and their thick coats of hollow-shafted hair and dense hide keep them warm, even at 40-below zero.

Whether they migrate, hibernate or tough it out by enduring a meager existence, Michigan's wildlife has developed some fascinating adaptations to survive almost anything Old Man Winter can dish out.