These areas are vital to marine mammals and migrating birds, and to polar bears, which often hunt in such places. Ringed seals are the bears' principal prey. They also hunt bearded seals and occasionally the more dangerous walrus. Normally solitary hunters, they have an impressive range of strategies, learn quickly, and show immense patience, power and speed. It has been calculated that their caloric needs require one ringed seal every six and a half days.
Arctic foxes live on the sea ice in winter by scavenging polar bear kills.
Since their prey is available year-round, polar bears do not hibernate like brown bears, except pregnant females, who spend about five months in dens to give birth to their cubs. The female must greatly increase her weight, mostly in fat, to carry off a successful pregnancy and denning. Cubs generally remain with their mother for two and a half years. Females are therefore able to bear young only every three years. This low rate of reproduction is balanced by a long life and low rates of natural mortality.