Polar bears reproduce via internal fertilization, with one male mating with several females during the mating season, staying with each for their three-day period of fertility. Mating occurs between late winter and early spring, after which gestation lasts anywhere between 195 and 265 days due to the females' ability to delay fetal development. Litter sizes range from one to four cubs but average two cubs per litter.
Polar bear cubs are born between November and January in dens dug in snow to hibernating mothers, and they nurse while the mothers continue to hibernate. They are born unable to open their eyes and weigh between 22 and 33 pounds. They remain with their mothers until they are 2 or 3 years old, and they reach sexual maturity at 5 or 6 years old. At adulthood, the females weigh between 330 and 660 pounds and are around 6 feet in length, while the much larger males are between 660 pounds and 1,760 pounds and can be over 8 feet long.
Polar bears are solitary animals that gain the vast majority of their nutrition through hunting. They primarily hunt ringed seals but will also eat several other seal species, as well as walruses, sea birds and other animals. It is common for polar bears to eat only the blubber of their prey, leaving the rest for scavengers.