Polar bear

The polar bear is the world's largest terrestrial predator, and the largest polar bear measured was 1,002 kilos.

The animal spends most of the year along the edge of the pack ice and its fur insulates so well that there can be a temperature difference of 69 degrees Celsius between the outside and bottom of the fur.

Even the soles of its feet are covered in fur, which allows the polar bear to walk without making noise and glide across the ice. It also has webbed feet halfway between the toes.

Although it normally moves around at a slow pace, it can travel at speeds of up to 50 kilometres per hour. Polar bears cannot maintain this speed for long as they risk dying from heatstroke because their fur insulates so well.

• Distribution: Arctic coastal areas and drift ice
• Population: All countries where polar bears live have polar bear protection programmes and hunting is controlled. The population is estimated to be around 22,000 animals. The future of the polar bear depends on how the Arctic environment is preserved. Restricted hunting in Canada and Greenland
• Weight: Male: 350-650kg. Female: 150-250 kilos
• Shoulder height: Male: 160 centimetres. Female: Slightly smaller
• Body length: 2-3.5 metres
• Mating season: Late March to early June
• Gestation: 7-8 months
• Number of cubs: 1-3 (usually 2 cubs)
• Food: Mainly seals, but polar bears are also scavengers. In summer it also eats vegetable food items.
• Zoo menu: Meat and fat, rats, mice and guinea pigs, herring and other dead fish, boiled and raw egg yolks, fruit and vegetables, grass, branches, rice pudding made from milk, trout pellets, jam, honey, cod liver oil, biotin, vitamins and minerals and oak bark chalk.
• Life expectancy: 15-18 years in the wild, in captivity 25-30. The oldest known polar bear lived to 42 years in captivity.
• Latin name: Ursus maritimus

Pregnancy and labour

The polar bear's pregnancy and birth are carefully adapted to life in the Arctic regions. The female can pause her pregnancy so that the cubs are always born in winter. The cubs are born in a cave in the snow, where they stay with the mother and grow until spring and the food supply in the form of seals returns.

The first three days are particularly critical for polar bear cubs. The cubs are born with a small reserve that gives them the energy to seek their mother's teats and access her milk, but if they don't get enough nutrition in the first two to three days, they won't survive.

Polar bears usually give birth to one to three cubs, but it's actually extremely rare for all of them to survive. When a cub dies, it is only natural for the mother to eat the cub. This is partly to keep the den clean and partly to avoid wasting energy and protein while staying in the den with the cubs.

In the wild, the polar bear mother will make sure to put on a solid layer of body fat before giving birth, as she and her cubs are isolated in the den for several months without access to food. During her time in the den, the mother loses several kilos, while the cubs grow bigger.

Milk as rich as cream

Polar bear cubs are on a diet while they are in the maternity den. From a birth weight of just 500 grams, they grow to 10-15 kilos before they emerge. Polar bear milk contains around 30 per cent fat, so the cubs will quickly gain weight. In the early days, the cubs spend all their time sleeping and eating, and the mother makes sure to keep them close to her at all times. This is partly to prevent them from freezing and partly so they don't waste precious energy crawling around the burrow. The more inactive the chicks are, the faster they grow. When they are very young, the chicks typically lie between their mother's legs, where it is warm and safe. You can often see her sticking her snout down to them. This is because it's her exhaled air that warms the babies and keeps the air in the den warm. Therefore, it's also an advantage that the maternity den is as small as possible to minimise the amount of air that needs to be heated.

The chicks will stay with their mother until they are around two and a half years old. They will continue to suckle with her for most of this period, but when they emerge from the den, they will slowly start eating solid food. When the chicks are big enough to fend for themselves and the mother is ready to be mated again, she will send the chicks away by clearly rejecting them.