Polar bear reproduction
Spring: Looking for a mate
Adult polar bears are solitary, but not anti-social: they actively seek mating partners in the late spring and early summer.
Males seek out females by following their scent. Two males may fight over a female.
Polar bears couples are only together for about a week before they separate. The male may then seek out another mate (a behaviour known as polygyny) .
Watch: a polar bear meets a potential mate on the sea ice in the first ever collar-cam video.
Food can be scarce for polar bears in the Arctic summer.
Some bears follow the ice - and seals onto the ocean, while others scavenge for eggs and other land-based food. Where polar bears are forced to spend the summer onshore due to lack of sea ice, pregnant polar bears may live off fat reserves for up to 9 months.
Summer sea ice is disappearing. It is projected to be nearly gone by 2040.
Autumn: Digging a den
In most areas, pregnant polar bears dig dens deep in snow drifts on land or on the sea ice, where they will wait to give birth during the winter. In Canada, some bears build dens in frozen peat banks.
Expectant mothers use these dens to rest and keep warm during the harsh Arctic winters.
Winter: Raising cubs
After two months or so in the den - usually between December and January - a mother welcomes cubs into her den. She may have up to three, but 1-2 are more common.
Between the snow den, their mother's body heat and milk, the cubs grow fast before they leave the den in March or April. The cubs take short field trips from the den to get used to outside temperatures before learning to live and hunt on the frozen ocean.
After 2 years together, the family disperses and the cycle begins again. Females begin to mate around the ages of 4 or 5. Males take longer to mature and usually begin attempts to mate around the age of 5 or 6, though their prime breeding years begin around age 10.
Polar bears are excellent swimmers, but their preferred habitat is on top of the ice that covers the arctic seas much of the year. That is where they mate, hunt and rear their young.
Large carnivores are sensitive indicators of ecosystem health. A polar bear at risk is often a sign of something wrong somewhere in the Arctic marine ecosystem.