Watch Wildlife Throughout The Winter Months
Durango Herald, February 9, 2003
Leigh Gillette

For animals that cannot migrate or otherwise cope with the challenges of winter, hibernation (or another sleep dormancy) is their survival solution.

Many of us celebrate winter as a time of outdoor adventure tempered by returns to indoor havens. For wildlife, surviving frigid temperatures, snows, and food shortages requires incredible coping strategies such as migration, hibernation, or special physical and behavioral adaptations.

Animals that cannot cope with winter, don’t! Instead, they migrate to warmer climes. A vee of geese in the fall sky is the classic illustration of this winter survival strategy. Most song birds travel hundreds of miles in their journey from the frigid north to the balmy south, following their food supply.

Many animals also migrate vertically, moving from higher elevations to lower. Deer and elk take this route, especially during heavy snow years. Traveling through deep mountain snow is exhausting, so they move to the valleys, where there is less snow to walk and paw through in search of food. Juncos, the small, dark headed birds that we often see feeding on the ground beneath bird feeders, are also vertical migrants. They frequent the mountains during the summer, but move into the lowlands each winter, seemingly falling with the first winter snow.

For animals that cannot migrate or otherwise cope with the challenges of winter, hibernation (or another sleep dormancy) is their survival solution. While many animals sleep through the winter, the relative depth of this sleep varies. “True hibernators” are those animals that allow their heart rate to drop radically and whose body temperature hovers just a few degrees above freezing. For example, the ground squirrel’s heart rate drops from 350 beats/minute to just two, and its body temperature goes from 98º F to 34º F. Marmots and little brown bats have similar true hibernation metabolisms.

Like a true hibernator, the black bear’s heart rate slows dramatically, but its body temperature only drops a few degrees, leaving scientists to debate how to define this “milder” version of hibernation. In complete contrast, skunks and raccoons are considered “light sleepers,” undergoing only slight changes in temperature and heart rate, and awakening during warm spells to leave their dens and feed.

Amazingly, there are animals that thrive in snow and cold. Ideal winter adaptations include wearing white camouflage, being able to keep warm and move easily in snow, and using available food sources. Examples are the snowshoe hare, weasel (or ermine), and ptarmigan (a grouse-like alpine bird). Each wears a brownish coat from late spring to fall. As winter approaches, the brown is gradually molted or shed and replaced with white fur or feathers.

These animals travel easily in the snow. The snowshoe hare and the ptarmigan have large “snowshoe feet” allowing them to float atop the snow as they travel. The lightweight weasel bounds across the snow, or tunnels straight though it, torpedo style! To stay warm, the weasel and ptarmigan burrow beneath the snow, while the hare grows a luxurious winter coat and shelters beneath the boughs of evergreen trees.

Each of these animals’ food is consistently available in winter. The weasel catches rodents beneath the snow pack (and lines its snowy den with rodent fur!) and the hare and ptarmigan nibble plant buds and shoots.

Take time to appreciate local winter animals. Enjoy migrant juncos at your birdfeeder, watch for raccoons during warm spells, or head to the high country to track snowshoe hare. Don’t hibernate!