Polar Bear
Reproduction
Polar Bear, Ursus maritimus, mother with cubs. Churchill area, Manitoba, Canada
© Michel Terrettaz/WWF-Canon
Polar bears are usually solitary animals, but in southern areas of the Arctic they gather together on land during the ice-free seasons in order to mate.
Polar bears breed in the summer months from March through to June.
The males actively seek out females by following their scent as they roam the sea ice. Once found, the male bears may engage in fighting if competing for the same female.
They remain with the female for a short time, about a week, and then leave in search of another potential mate. Only pregnant female polar bears stay in dens during the winter.
So in late autumn/fall, from October through December, pregnant females begin searching for suitable denning habitat on land or on the sea ice. They then dig their dens in deep snow drifts while the rest of the polar bear population remains active on the ice throughout the winter.
Quick Facts
- Females begin to breed at 4 to 5 years of age
- Males can breed from around 6 years
- A female will often double her bodyweight through eating in order to have enough reserves to care for the cubs
- While in the "maternity den" a polar bear's heart rate slows from 46 to 27 beats per minute
- Cubs are born between November and February
- They weigh less than 0.9kg (2lb) when born (about the size of a guinea pig)
- Average litter is 2 cubs
- They leave the den when the cubs are 10-15kgs (22-33lbs)
- Polar bears can live to around 25 years
- Old bears are thought to die from starvation as they get too old to hunt
In the Beaufort Sea, some polar bears dig maternity dens in snow drifts on multi-year ice floes (i.e. over permanently frozen sea), while in the western and southern Hudson Bay, in Canada, cubs can be born in dens excavated in frozen peat banks.
After about two months the cubs, usually two of them, are born in the den.
The timing of the birth is sometime during early winter between December and January.
Pregnant females must live off stored reserves for up to 6 months.
The snow den, mother’s body heat, and her milk - high in fat content - enables the cubs to keep warm and grow rapidly before leaving the den in March or April.
Short trips are made to and from the den for several days as the cubs get used to the outside temperatures. Then the family leaves and makes its way to the sea ice where the mother teaches, hunts for and protects her cubs.
After two years together, the family disperses and the cycle begins again.
