Arctic Land Mammals
It is vital for a mammal, being a ‘warm-blooded’ vertebrate, to keep warm in order to maintain its body at a constant temperature. If it cannot do this it will die. The Arctic is the coldest place inhabited by land mammals and these have very thick fur, which insulates the body by trapping air. They also have a layer of stored fat under the skin which gives additional insulation.
Like many Arctic mammals, the polar bear has white fur made of hollow hairs, which traps and warms air. Ultra-violet light is funnelled from the sun down the hairs to the bear’s black skin, changing it into warmth. The dense undercoat is covered with an outer coat of long guard hairs. These help to keep the polar bear dry and warm while it is swimming. To find out more about the life of polar bears visit our Polar Bear factsheet.
The body shape and size of many cold climate mammals differ quite a lot from similar species living in warmer areas. Generally an animal becomes rounder and bulkier when its environment is very cold. Also its legs, ears and tail are shorter. These adaptations help to conserve heat. In short, a football-shaped animal would be warmest of all.
The Arctic fox, although certainly not as round as a football, does differ in shape from our red fox in Britain. It has a rounder, plumper body, shorter legs and tail, as well as a shorter muzzle and ears than the red fox. The thick fur turns white in the winter and the soles of the feet are covered in fur. All these adaptations allow the Arctic fox to cope with an outside temperature as low as – 40°C.
Arctic hares show similar physical adaptations to the cold. They have shorter ears and shorter, stockier legs than the brown hare of Britain. The snowshoe hare has similar sized ears and legs to the Arctic hare, but in addition it has its own built-in snowshoes i.e. enlarged hind feet, which help it when crossing soft snow.
Antarctic Survivor – the Emperor Penguin
The land mass surrounding the South pole, the Antarctic, is the coldest place in the world! The temperature has been known to fall as low as –83.3°C. Like all Antarctic penguins, the largest of them all, the emperor penguin, has a thick layer of densely packed feathers (about 12 to the square centimetre), and tufts of down at the base of each feather which act like a thermal vest, trapping air to keep the bird warm. The tips of the outer feathers are broad and curved, overlapping like roof riles – this makes the bird waterproof. A thick layer of blubber (fat) also helps to keep the penguin warm when swimming in the icy ocean. To help it adapt even more to the intense cold of its habitat, this penguin has special nasal passages so that it loses very little heat when breathing out. Its flippers and legs are also specially adapted to reduce heat loss.
Winter in the Antarctic begins in March and whereas other animals sensibly make their way to the warmer parts of north Antarctic, the colonies of emperor penguins march across the pack-ice about 200 miles in the opposite direction, to breed in the coldest place on Earth! The breeding sites, called ‘rookeries’, may be many miles from the sea and number up to 25,000 birds. The parents do not make a nest. To begin with they both take it in turns to protect the egg from the ice by resting it on their feet, raising their toes to keep it well off the ground. The female then returns to the sea to feed, leaving the male to incubate the egg for nearly three months. He uses a fold of skin, which hangs over the egg, to keep it warm. The male eats nothing, relying on his reserves of blubber to keep him alive. Hundreds of incubating males may huddle together for warmth. They will have lost almost half of their original body weight by the time the egg hatches.
The female returns to the rookery when the chick is ready to hatch and takes over the brooding of the down-covered baby, feeding it with regurgitated food. The hungry, exhausted male trudges back to sea to feed.
As many as 6,000 emperor penguins may huddle together to form a ‘tortoise’. They take it in turns to move into the middle where it is warm.
Keeping Warm in Water
Marine mammals, such as seals and whales, live around both the North and South Poles. The heat from a warm-blooded animal is absorbed by cold water faster than it is by air. A human being would survive for only a few minutes in the freezing polar seas but the bodies of seals and whales are adapted so that they can keep warm. As with the land mammals their shape is rounded but a fur coat would not be much good for trapping heat underwater; instead they have a very thick layer of blubber to keep body heat from escaping.
Fish, like reptiles and amphibians, are ‘cold-blooded’ vertebrates. This means that their body temperature varies according to the temperature of their surroundings, unlike mammals and birds which can control their body temperature so that it remains steady. So, how do fish in polar waters manage to avoid freezing to death? Some Antarctic fish stay deep in the sea, where although the temperature may be –1.8°C, it is a fraction warmer than the freezing point of sea water, so no ice forms inside their body. Most Antarctic fish, called Notothenioids, even have their own ‘antifreeze' made up of special proteins in their bloodstream.
Keeping Warm Under a White Blanket
Another adaptation for many plants and animals is to make the most of a blanket of snow. Air is trapped amongst the snow flakes as they fall and this provides good insulation. The temperature under a layer of snow does not usually fall below freezing. The heat from any animals or plants under the snow is trapped in a warm ‘igloo’. Small mammals such as mice, voles and lemmings can remain active throughout the winter, searching for plant food in a network of tunnels under the snow. The polar bear digs out a den on snowy slopes to give birth or shelter during blizzards. It curls up and lets the snow drift around its body to form an insulating layer.
Many plants also survive in warm pockets under the snow, waiting for the snow to melt so they can then burst into growth. If winds blow the snow away they may become frozen.
A local name for the familiar snowdrop is the ‘snow-piercer’. The tip of the flowering stem is covered by a special protective leaf and this allows the snowdrop flower to force its way up through the snow.
Image: Survival at the Poles by Ian Duffy