Dressing for Winter
It's wintertime and many snow-dwellers have donned their winter wear, from white fur (or feathers) to specialized foot gear. Weasels have shed their brown fur for ermine cloaks. Arctic Foxes pad along on the surface of the snow on thick, furry snowshoes. In northern landscapes both predator and prey may grow a white winter coat to help them blend in with their background. But this winter dressing must also keep them warm, dry, and mobile. Is a white coat warmer than a dark one? What other tricks help keep Arctic birds and mammals warm? Read on to learn some of the ways northern animals dress up for winter!
It's in the Air
The white fur or feather coat of the far north must serve a dual purpose: It must provide camouflage against the snowfields and, just as importantly in frigid climes, it must be warm. Luckily, it is not necessary to sacrifice one for the other. If dark colors absorb heat and white reflects it, how is it possible that a white coat provides adequate warmth? The answer is in the air . . . that is, the answer is the air.
It is not the color white that gives the white feathers of the ptarmigan (a grouse-like ground bird) or the white hairs of the Polar Bear their extra-warming quality. Rather, white is the absence of pigment, and the cells in white hairs and feathers, thus empty of pigment, are filled with air. This provides thermal insulation, similar to the way fluffy down feathers provide warmth by trapping air in the spaces between the tiny feather barbs.
Snowshoes and a Snow Blanket
Many of these northern white-cloaked creatures have other tricks up their sleeves as well. Ptarmigan, plant-eating birds mainly of the northern tundra, have white winter plumage that helps them hide from predators. Thick, long feathering extends over their legs and feet, down to the toes, both providing warmth to their extremities and enabling them to walk more easily on the snow surface. These birds do not have down feathers, as some birds of the far north do. However, many of their feathers sport an "after-shaft," an additional, smaller, fluffier feather growing from the base of a main feather and probably providing extra insulation. And if all else fails, a ptarmigan will escape from the cold by plunging into a bank of snow! In fact, ptarmigan habitually roost under the snow. There, again, air provides the key to thermal insulation.
The seasonal molt, when the coat of an animal changes color, is a photoperiodic phenomenon governed by lengthening or shortening periods of daylight. As daylight diminishes in autumn, many northern animals will begin to grow thicker and lighter-colored coats that eventually become completely white. Likewise, as the days lengthen in spring, the winter coat is gradually shed (in mammals) or molted (in birds) and replaced with a darker color.
As a whole, which animals change to a white coat in winter and which do not seems to be determined mainly by the climate and latitude of the area in which they live. However, studies of the Long-tailed Weasel suggest that among individuals, the propensity to molt to a white winter coat may be influenced by other factors. In the northern part of their range, most Long-tailed Weasels turn white in winter; in the central part some individuals molt to white while others remain brown all year; and in the southernmost part no individuals change color for winter. But if a northern weasel is captured and taken south, it will still turn white in winter, no matter whether snow falls or not!
Foxtail Scarf and Lucky Rabbit's Foot
Unlike its fellow far-northern carnivore the Polar Bear, the Arctic Fox doesn't remain white year-round. Most individuals are gray-brown in the summer months, when the ground is snow-free, and white in winter. This creature needs to stay camouflaged because it doesn't want to be seen by anybody, up or down, on the food chain. The Arctic Fox is both predator, mainly of small rodents such as lemmings and voles, and prey, to Polar Bears, Wolverines, Golden Eagles, and Snowy Owls. Thus, Arctic Foxes adapt their wardrobes to the climate: Those that live in areas without much snow tend to stay gray-brown all year, those in areas of permanent snow and ice stay white, and those in areas with snow only part of the year change seasonally.
The Arctic Fox's white winter coat is thicker and warmer than its summer coat. Its tail is long and fluffy and can even be used as a sort of scarf to cover the face. Its feet become almost completely wrapped in fur in winter, and it runs along the snow in warm, slip-proof snowshoes. Interestingly, its scientific species name, lagopus, means hare-footed, and its furry winter footwear recalls that of its northern neighbor the Snowshoe Hare. This hare, prey to a wide variety of raptors and carnivores (most prominently the Lynx), exhibits a fascinating seasonal molt from its winter whites to its summer browns, with the changes in its coat color paralleling the changes to the surrounding landscape. In autumn, when its white fur is only partly grown in, the ground is often likewise covered only partly with snow. When winter arrives and the northern landscape is cloaked in snow and ice, the hare is cloaked in white. And when the melting begins in spring and patches of ground begin to show, so do patches of brown occur in the fur of the Snowshoe Hare. This is truly a four-season coat!
Top of the Heap
While ptarmigan, weasels, Arctic Foxes, and Snowshoe Hares change with the seasons, turning various shades of brown when the snow melts and white in areas of snow cover, the Polar Bear, living in year-round snow and ice, remains white in all seasons. What's the advantage to wearing a white coat year-round? Camouflage and flotation! In the case of the Polar Bear, occupying the top of the food chain in much of its habitat, the white fur coat isn't needed to hide from predators -- rather, it is needed to hide from prey. Blending in with the snow and ice helps the bear make sneak attacks on seals, fish, birds, and other creatures. The coat is made of two layers, a soft, furry, warm undercoat, and an outercoat consisting of longer, coarser guard hairs. The white guard hairs are hollow, air-filled shafts, which makes them both insulating and buoyant in water -- quite useful qualities when one is swimming among the ice floes.
Beneath the white fur, the Polar Bear's skin is black, which helps it absorb and hold heat from sunlight. Beneath that is a layer of fat, said to reach a thickness of more than four inches, which provides further insulation. The heavy fur covering a Polar Bear's feet provides both warmth and traction on ice and snow. And at about 9 inches wide and 12 or more inches long, each foot serves as a handy snowshoe, facilitating movement on the snowy surface. Yes, this enormous and formidable Arctic carnivore is certainly well dressed for the weather!
Click the species below to learn more about creatures that dress for winter: