Arctic animals are animals that have adapted physically and behaviourally to the particular conditions of life in the most northerly region of Earth. The Arctic can be defined in various ways.
Arctic animals are animals that have adapted physically and behaviourally to the particular conditions of life in the most northerly region of Earth. The Arctic can be defined in various ways. Geographically, it is that part of the world lying north of the ARCTIC CIRCLE (66° 32´ N lat) beyond which there is at least one day in the year in which the sun never sets and one in which it never rises.
Ecological definitions invoke the major discontinuities: on land, the major break is the TREELINE; in the sea, it is where the characteristically cold, low-salinity arctic waters meet Atlantic and Pacific waters in zones of upwelling and mixing. Typically, the lives of terrestrial and aquatic members of the arctic fauna are closely linked. The sea provides a food source for land birds (from snow buntings to whistling swans) that forage in spring on seaweed windrows on storm beaches; winter ice provides access to marine life for arctic foxes, wolves and POLAR BEARS. Conversely, many marine animals (from murres to walrus) use parts of the land for mating and raising young; others, such as ringed seals and ivory gulls, can raise their young on ice and thus be independent of the terrestrial environment.
The arctic land fauna resembles more familiar faunas of the northern temperate zones; fewer species are present, but they are generally of the same orders and families as those farther south. The deficiencies arise for several reasons. On land, mean annual temperatures are below freezing and the ground remains frozen at depth; therefore, no warm layer persists near the surface through the winter. Hence, reptiles and most hibernating mammals are not found north of the line of continuous PERMAFROST. Because trees are absent, certain boreal-zone insects, rodents, carnivores and birds that depend on them for food and shelter disappear.
Open water is scarce in most of the Arctic throughout most of the year. Except where rapids and tiderips occur, solid ice or dense pack generally forbids access to the aquatic environment. Animals wintering on the arctic TUNDRA must quench their thirst with snow. Fish-eating birds and mammals typically migrate for the winter to areas providing better access to prey; the remainder concentrate at the scattered polynyas (ice-free refuges).
The characteristic that most restricts opportunities for animal life may be the brevity of the arctic growing season. The land vegetation produced in the few but long days of the arctic summer must sustain life over an extended, harsh and demanding winter. It is hardly surprising that the most mobile animals pass the winter elsewhere: birds on ocean coasts farther south and in interior plains and forest lands; and many barren-ground CARIBOU on lichen pastures of the open BOREAL FOREST.
The short growing season tends to squeeze certain species out of arctic ECOSYSTEMS entirely. Beyond the edge of the barrens, it is rare to encounter the plagues of blackflies inevitable in the boreal forest. The absence of bats and swallows might be attributed to the very short period in which flying insects are available as food.
Another serious constraint is the dangerous heat loss caused by low winter temperature and high windchill. This factor imposes on warm-blooded animals the need for a thick, dense, insulating coat, which means that surface-wintering arctic animals must generally be large. The larger the animal, the greater the body mass to skin-surface ratio and the smaller the relative heat loss. Northern ravens and arctic foxes are the smallest animals found above the snow surface during the arctic winter.
Hard-packed snow denies the use of drifts for shelter to animals (eg, grouse, ungulates), who use the softer drifts of the boreal zone for that purpose. Animals using the solid arctic snowdrifts for shelter include the collared lemming, which grows special winter claws for the purpose, and the polar bear, which burrows in for its winter and maternity dens. The ringed seal is unique in constructing its maternity den in snow on the surface of land-fast sea ice.
Food sources may be few, sparse and evanescent. Most arctic species have adapted, and as a result are quite opportunistic. To the south, insects typically feed on one plant species only and birds and mammals have relatively fixed diets; in the Arctic, exploitation of broader food resources (ie, trophic niches) is common.
The polar bear provides one example. Bears are typically omnivorous. Polar bears are also amphibious and able to subsist on very diverse and meagre resources, both terrestrial and aquatic, for long periods each year. Among birds, the long-tailed jaeger is equally well adapted. During the brief arctic summer it is an eater of terrestrial arthropods (especially spiders and midges), a bird hunter (particularly of nestlings), a lemming catcher, a sea-food gatherer of the tidal flats and a carrion seeker.
The modern Canadian arctic land fauna may be traced back to the Pleistocene epoch (see ICE AGE). A few thousand years ago, during the last continental GLACIATION, thick sheets of ice covered most of Canada and much of the northern US. Arctic animals have descended from species that occupied land that was revegetating after the retreat of the ice.
At least 2 sources of origin are evident: the west, where ice-free land extended from the Yukon Territory and Alaska, under what is now the Bering Sea; and the south, which can be visualized as a zone, like that near the foot of a modern glacier, subject to cycles of improvement and deterioration. Presumably, the brown lemming, grizzly bear and barren-ground caribou came from the west; the northern red-backed vole, red fox and moose from the south.
A few species, including the Peary caribou, which may resemble more closely the Svalbard reindeer than other North American caribou, and the large, upright-hopping arctic hares of the Queen Elizabeth Islands and northern and eastern Greenland seem likely to have come from a third, High Arctic source area. Polar bears and arctic foxes are so at home on sea ice that they live wherever the ice pack has reached the shore.
Compared to the land, sea and lake waters remain within a narrow temperature range year-round. However, the seasonal fall in temperature affects the aquatic environment profoundly by causing surface water to freeze to a depth of 2 m or more. Ice, particularly when covered with snow, impedes penetration into water of the solar radiation necessary for photosynthesis. Furthermore, bottom freezing and scouring by drifting ice floes greatly reduces the productivity of arctic intertidal and near-shore marine zones. Marine productivity is comparatively low, limited by temperature and the availability of nutrients and light. Because of dangerous ice cover and limited winter productivity, several populations of marine mammals winter in open and more productive seas.
Marine vegetation includes benthic (bottom-dwelling) and planktonic (free-floating algae) and algae that live within the lower levels and coat the submerged surfaces of floating ice. This living material feeds the zooplankton preyed upon by arctic and polar cod, by birds such as murres and guillemots, and by marine mammals such as the ringed seal. Algae also feed the molluscs, which sustain the walrus.
The predators highest in the food chains of the arctic seas are polar bears and killer whales; important scavengers include glaucous gulls, amphipod crustaceans (which attack fish and seal carcasses left too long in nets) and Greenland shark (lethargic fish attaining lengths of about 3 m). The arctic char, the most important arctic food fish, lives its first year in lakes but, where passage exists, takes up an anadromous habit in later life (ie, it migrates to coastal waters for the summer to feed voraciously on crustaceans and other small marine animals, and returns to spawn in lakes in autumn).
The arctic fauna forms the basis for local subsistence economies and, being partly migratory, supports food, trade and recreation elsewhere in the world. Snow geese hatched in the Canadian Arctic are hunted as far south as the rice fields of Texas; harp seal populations, which summer in arctic waters, are harvested in the Gulf of St Lawrence.
The earliest known arctic peoples used small stone blades and points suitable for killing thin-skinned game, eg, caribou and birds. Later cultures depended on sea mammals, particularly the bowhead whale. This, the largest arctic species, was greatly reduced by American and Scottish WHALING in the late 1800s, and is now the only truly endangered arctic mammal. The odd one is still occasionally killed off the north coast of Alaska and the Eastern Arctic.
The Inuit of the historical era have largely been dependent on sea mammals, particularly the ringed seal, which stays in the frozen arctic bays and straits all winter, scratching breathing holes through the ice. The hunter would wait at such a hole and harpoon the animal as it rose to the surface.
Seals provided fuel (seal oil), skins (used for summer boots and tents) and meat. Warm clothing has always been essential in the Arctic; the bearskin winter trousers of the Greenland hunter have been as distinctive as the guardsman's busby. Caribou killed in August, when the new hair is still short and fine, provided the most popular clothing skins. Muskox robes and skins of caribou killed in winter were used for bedding. The trade in arctic fox furs began in earnest in the early 1900s. Because both the fox populations and the value of the furs fluctuate so greatly from year to year, trapping in the Arctic yields an uncertain return.
With social and industrial development, CONSERVATION of arctic fauna has demanded increased attention. Recent developments include restrictions by the US on the import of sea mammal products; imposition by the International Whaling Commission of quotas on the take of bowheads by Alaskan native hunters; signing of an international convention on the conservation of the polar bear (particularly on the high seas) by the US, Norway, Denmark, the former USSR and Canada; and the devolution of game management authority to Canadian Inuit organizations after land claim settlements.
The economies of native villages dependent on cash from sales of wild furs are increasingly menaced by international "animal rights" lobby groups, though rights cannot be conferred but only reallocated; in this case from fellow human societies to animal populations, or vice versa. However, renewed interest in oil exploration and production, offshore drilling and year-round shipping is of the greatest concern to environmentalists and native groups. For example, a large barren-ground caribou herd calves in the Arctic International Wildlife Range in northern Alaska, which is expected to be open for oil exploration quite soon.
Other threats to arctic animals may include the impact of pollution (industrial and military) from the south on more fragile ecosystems, the threat of OZONE LAYER depletion on high-altitude biota, and more harvesting pressure as human populations grow.