Although most female polar bears make very good mothers, six out of 10 polar bear cubs die in their first year—victims of starvation, predation or accidents. Among the threats to cubs are adult male polar bears, which sometimes attack the young and eat them. For this reason, females with cubs generally avoid male bears. Highly protective mother bears are capable of driving off much larger males.

Young bears are considered "subadults" until they reach maturity at age five or six. The leading cause of death for this age group is starvation. Those polar bears that manage to survive to adulthood have learned to master the challenges of Arctic life.

After polar bears reach adulthood, the annual mortality rate is surprisingly low—as little as five percent a year. An adult polar bear's only enemies are humans and, on rare occasions, other bears.

In the wild, adult polar bears live an average of 15 to 18 years, though biologists have tagged a few bears in their early 30s. In zoos, many captive bears live until their mid- to late 30s. One individual at the Detroit Zoo lived to the ripe old age of 43.