The World of Polar Bears

Females are sexually mature when they are 3–6 years old. Males reach sexual maturity at 4-5 years of age, but are generally not successful breeders until after 6 years of age. The breeding season for polar bears is March through May. A male will find a female by following her scent and tracks across the sea ice. After mating, the development of the fertilized egg (blastocyst) is delayed and does not implant in the female’s uterus until August. Once the embryo begins to grow, the gestation period is only 4-5 months. In October and November, a pregnant female will find a denning area either on land or on the sea ice. She creates her den by making a depression in the snow on a bank or slope or near rough ice. As snow drifts form, she will increase the size of her den. The cubs (usually twins) are born in December and weigh 1-2 lbs and must remain in the protection of the den until they grow bigger.

By late March or early April when the cubs weigh ~15 lbs, they leave the den. For the first few days, the family will make short trips and return to the den giving the cubs time to acclimate to the temperatures outside. After this time, the group will travel to the drifting sea ice. The cubs will remain with their mother for about 2 years and then the female will mate again.