November 26, 2012
Winter: Migrate, Hibernate, or Tough It Out
How your wild neighbors survive the cold season
Just how do your wild neighbors cope with winter’s woes? In some regions, cold temperatures, deep snows, whipping winds, and dwindling food supplies make life tough.
Leaving town: Birds often migrate to warmer climates. But not every migration requires wings and a long-distance journey. Elk, for instance, may trek 4,000 feet down a mountain to benefit from weather similar to that found 1,200 miles southward.
Checking out: Hibernating or becoming dormant works for species such as woodchucks and bears, who live off stored fat during cold months. Body-chemistry changes in some frogs enable them to overwinter in a frozen state and then thaw out when spring returns.
Extreme measures: Many insects' life spans come to an end in winter—right after they've laid eggs that will hatch when the earth is warm again.
The animals who stay put and awake in winter are helped by changes their bodies make in response to reduced daylight. They also adapt their behavior to survive the cold.
Insulating—inside and out
High-tech coats: Fur and feathers wrap the body in warm air. In winter, the length and density of deer's guard hairs and underfur both increase. Red foxes and porcupines grow a thick underfur. Many birds, such as goldfinches, grow 50 percent or more feathers in winter.
Life-saving fat: Added fat also improves winter survival. Animals such as deer live off fat stores when they can't find food. Dark-eyed juncos eat steadily to gain fat each day, but it's only just enough to get them through the night.
Cool chemistry: Goldfinches' bodies are able to break fat down faster when they need extra help keeping warm.
Sunny slopes and cozy woods: Deer seek southern slopes in the day, bedding in depressions in the snow and soaking up the sun. At night they gather in the woods, where the trees insulate them from winds and the cooler temperatures. The woods also provide warmth from the heat they absorb from the sun during the day.
Secret world beneath the snow: Mice and voles live beneath snow packs of 6-10 inches or more in a space known as the sub-nivean. These creatures depend upon a snow blanket for shelter from extreme cold and winds, so a frost before the snow can be deadly.
Modifying body temperature: On cold nights chickadees save energy by allowing their body temperature to drop ten degrees, but they still must shiver all night long to generate body heat.
Following trails: Moose are built to be able to move through chest-high snows. These and other trails are used by white-tailed deer, foxes, and other animals, who save energy by following in other’s footsteps.
Changing their ways: When food is scarce because of snow, deer rest, often among evergreens, if available, when the effort to forage would use more energy.
Becoming “winter-social”: Voles and other small mammals will huddle together to reduce heat loss during unusually low temperatures or thin snow packs. White-footed and deer mice have even been found sharing winter nests. Even raccoons are known to huddle in communal winter dens for warmth.
Where you come in
You can help your wild neighbors survive by providing a steady source of fresh water in a heated birdbath. It’s a small effort that provides a life-saving benefit for them and great bird-watching opportunities for you.
Explore winter's wild world
» Heinrich, Bernd. Winter World: The Ingenuity of Animal Survival. New York: Ecco, 2003.
» Marchand, Peter J. Life in the Cold: An Introduction to Winter Ecology, Third Edition. Hanover, Mass.: University Press of New England, 1996.
» Halfpenny, James C. and Roy Douglas Ozanne. Winter: An Ecological Handbook. Boulder, Colorado: Johnson Publishing Company, 1989.