Adult wolves weigh between 85 to 115 pounds with some exceptionally large ones reaching 130 pounds. Females tend to weigh 10 to 15 pounds less than males. Juvenile females become sexually mature at two years of age, but the males do not reach sexual maturity until their third year. The oestrous period lasts for about a month in late winter, but the females are only in heat for the last five days of the period. The gestation period is about 63 days and in Alaska wolf litters vary greatly but average about six pups.
Females ordinarily produce a litter every year and mature females tend to produce larger litters.
At birth, wolf pups are blind and pug-nosed but by 12 days their eyes open, their ears become erect, and they can move about the den. Both parents care for the young and will mate for life or as long as both remain alive. When the pups are about two months old, they usually are moved from the natal den to another summer den for reasons of sanitation and perhaps better hunting. Food becomes more plentiful during the northern summer. Wolves can run up to 26 mph over a short distance and have incredible endurance for longer distances, but their long-legged prey can out run them in a straight race.