How land animals adapt to cold and snow
The Arctic winter is typically cold and snowy. Staying warm requires good insulation or shelter, or expending a great deal of energy. The snow cover offers shelter but may limit movement and access to food. To survive the harsh conditions of the far north, Arctic animals have developed many behavioral and morphological adaptations.
For large animals, thicker and denser fur or plumage may be adequate to hold an insulating layer of still air against their bodies. If so, they need to produce little or no extra heat to stay warm in cold weather. Small animals, however, cannot carry thick enough fur, and thus depend on other strategies. For instance, they use snow as shelter throughout the winter. Snow is an excellent insulator, and the temperature deep in the snow can be much higher than that in open air. Many northern grouse species stay in snow burrows during cold nights and poor weather. Even when the temperature above the snow is as low as -17°C, the grouse’s burrow may be above freezing. By creating a warm burrow, the grouse reduces its energy demands and thus its need for food. Even large mammals use snow for shelter. Brown bears hibernate under the snow, and pregnant polar bears make snow dens for the winter. Male polar bears make temporary dens during storms.
Another strategy for coping with high energy demands when food is scarce is to accumulate large fat deposits when food is available. Two extreme cases are the Svalbard ptarmigan and the Svalbard reindeer. In autumn, up to 30% of their body weight is fat. Moreover, many passerine birds, mammalian predators, and beavers store food to eat during winter.
While snow provides shelter for some animals, it causes problems for others. Deep and soft snow make it difficult for many animals to move, and may prevent them reaching the plants on which they graze. Some species have adapted by developing large feet for their body weight. The mountain hare, for example, has a foot that is twice the relative size of the foot of the European hare, helping it move over the snow without sinking. Lynx and Arctic wolves have large feet and long legs for the same reason.
By providing a white background, snow makes many animals highly visible in winter, even if they are well camouflaged in summer. Many northern species, such as ptarmigan and hares, have evolved to change the color of their fur or plumage to white in winter so that they retain their cryptic coloration year round. Some predators, like weasels and the arctic fox, also change their fur color between summer and winter. Whether this is to hide them from their prey or from potential predators is not clear.
Osmo Rätti, Arctic Centre, University of Lapland, Rovaniemi, Finland. From the CAFF publication, Arctic Flora and Fauna, www.caff.is