Winter Adaptations of Three Montana Animals

Bears

                                                                                                                                                           

When we thinks of bears during winter, we commonly think of hibernation. But, in fact, bears do not hibernate at all. They go into what is called torpor, or short-term hibernation. Torpor helps bears save energy during winter when food is harder to find. When the animal is in torpor, its heartbeat and temperature go down, but not as much as in true hibernators. This aids animals such as bears in colder climates because it helps the animal conserve energy. This is not as deep a ‘sleep’ as hibernation and can last a very short time.

Unlike animals that go through hibernation, bears can wake up fairly easily. When they do, they will occasionally leave the den, but for the most part they do not eat or drink during winter.  During this time, a bear loses 15 to 30 percent of its body weight--without defecating or urinating.  Instead, the bear recycles its waste.  It does this by breaking down the urea, which at high levels is fatal.  The resulting nitrogen is used to build protein, allowing the bear to maintain muscle mass and organ tissue.

Bears and Their Cubs

The bear cub is born mid-winter, blind, hairless, helpless, and weighing less than a pound.  The tiny bear cub is just a fraction of one percent of the mother bear's weight.  "It's almost an external pregnancy--the cub is born and then migrates to the teats and nurses," said biologist John Hechtel. "The size of the cub in the spring when it comes out of den is closer to what you'd expect to see at birth." The reason for this is bear milk, which is very high in fat. The hibernating mother bear is living off her stored fat, and it's much more efficient for her to put that fat into her milk than to convert it to sugars and proteins that must be transported through her blood to the placenta, then through the placental barrier to the fetus. The mother also cleans the cub, and, by consuming the cub's waste, everything is recycled.

Grouse

Resting place of a ruffed grouse just after its departure

The ruffed grouse is famous for its winter roosting routine, commonly referred to as “snow roosting.” If the snow is soft and a foot or more deep, the grouse is likely to spend the night in an insulated, air-filled snow tunnel. To do this, the grouse will fly directly into the snow. Then, with its wings and feet, the grouse extends the tunnel, sometimes to as much as 10 feet. Recent research suggests that the temperature in the tunnel can be as warm as 32 degrees Fahrenheit and that it rarely falls below 20 degrees. The tunnel helps the grouse conserve energy, so it needs less food. Less time spent in the open also means less time being exposed to predators.

Ruffed grouse are poor at storing fat, so the winter months are tough. This means grouse must eat large amounts of food daily to survive. However, this poses a challenge. If the grouse feeds for too long, it risks being exposed to predators such as the red-tailed hawk and the great-horned owl. To minimize the risk, grouse eat fast. In as little as 20 minutes a grouse can swallow enough buds to make it through the day.

Ruffed grouse have other physical and behavioral characteristics that help in winter. In September, fleshy projections—called pectinations—begin growing on the sides of their toes and stay until spring. These comb-like nubs increase the surface area of the foot and work like snowshoes, allowing the bird to walk across snow with less effort. Pectinations also give the grouse a better grip on ice.

Grouse feathers also adapt in winter. In cold weather, special feathers extend down the beak and cover the nostrils. This allows the grouse to breathe in warm air. Ruffed grouse also have feathers partially covering and insulating their legs.

Moose

Bull moose eating willows

Moose are long-legged and thick-bodied, adaptations that enable them to move about through deep snow and wet lands and to carry sufficient fat stores. Their thick, hollow hair is fatter at the tip than at the base. The shape helps trap an efficient insulating layer of air next to their bodies. But staying warm is not all the moose has to worry about.

 

For moose, winter is full of suffering and triumph over that suffering. But the suffering is not as a result of the cold. Because of their winter adaptations, the cold hardly bothers them. The struggle that moose face is finding food. During winter, moose mostly eat twigs from deciduous trees and shrubs and the twigs and needles of balsam fir and cedar. Each bite of food is a mere gram–just 1/28th of an ounce. Furthermore, twigs and needles contain only one third the nutrition of leaves that moose eat during summer.

The food is not only low in nutrition, but worse off, difficult to gather. The snow is deep and moving from tree to tree is difficult and energy consuming. An 800- or 1000-pound moose survives the harsh winter, chest deep in snow moving from tree to tree, on about nine thousand twigs a day.

   

 When snow is deep and food sparse, moose restrict their intake of food because the costs of eating exceed the gains. Moose pass much of the winter resting and hungry. Ultimately, moose lose weight every single day for about five months of the year. Nevertheless, most moose live to see the spring that follows each winter.