The World of Polar Bears

Reproduction

A. Sexual maturity

1. Female polar bears reach sexual maturity at about 4 years (Stirling, 1988).
2. Male polar bears reach sexual maturity at about 6 years (Stirling, 1988).
3. Most male polar bears don’t successfully mate until 8 to 10 years and older.

B. Mating activity

1. Breeding takes place in April and May on the sea ice.
2. During the breeding season, males and females find each other by congregating in the best seal-hunting habitats.
3. Male polar bears have been seen following the tracks of breeding female polar bears for more than 100 km (62 mi.). Scientists are uncertain what signals males use to track breeding females.
4. Competition for females is intense. Females breed about once every three years; therefore, there are about three adult males to every breeding female.
5. Before mating, a female polar bear may be accompanied by several males. The males fight fiercely among themselves until the strongest or largest male succeeds in chasing the others away.
   a. A polar bear threatening to attack another polar bear usually lowers its head, flattens its ears back, and gives an open mouth threat with a hisslike roar.
   b. Fights are rarely fatal, but do result in broken canines and scars on the head, neck, and shoulders.
6. Dominant males may succeed in breeding several females in a season.
7. Once paired, the male and female stay together for a week or more.
   a. Females are induced ovulators, which means the act of mating causes a female to release an egg for fertilization.
   b. Several days of mating interactions may be required to stimulate ovulation and guarantee fertilization of the egg.
8. Polar bears may have many different mates over their lifetime.