Posted by Janet Harriett on May.12, 2010

Photo Credit: US Fish and Wildlife Service

In May, Wildlife Wednesday looks at unique mothering styles in the animal kingdom. This week, we look at how polar bears deal with raising cubs in the harsh Arctic.

Like weasels, discussed last week, polar bears use delayed implantation to ensure that their pregnancies coincides with available food resources to nourish the unborn cubs. Polar bears mate in spring, and the mother polar bear “holds on” to the fertilized ova until after she’s fed through the summer and is ready to dig a maternity den for giving birth over winter.

Female polar bears dig maternity dens in the snowbanks or in permafrost near the edge of the sea, on land or in land-fast ice. Winter snows seal them into the den, where they give birth to 1-2 cubs and nurse them for several months, surviving off fat stores. The protected environment of the maternity den allows the cubs to mature so that they’re able to walk and learn to hunt by the time the family emerges from the den in the spring.

Since the implantation is delayed, the two cubs in a litter may be fathered by different male polar bears. The males, however, don’t play any role in raising the cubs during the 2-3 years that cubs stay with their mother. When the cubs are mature enough to strike out on their own, the mother or a potential mate chases the cubs off before the mother starts the cub-rearing cycle over again. A typical female polar bear will have about five litters during her life.

The polar bears’ strategy of maternity denning relies on colder winters to keep the ice stable. In a warmer arctic winters, the snow cover may not be adequate to protect the den over the winter. A maternity den on ice may break away from the land, flip or break open prematurely, reducing the odds that the cubs will survive. Fewer than half of all polar bear cubs survive to adulthood.

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Posted under Living, Nature and Environment.