Mating takes place during the spring months from late May through early July. Brown bears are serially monogamous and will remain with the same mate from several days to a couple of weeks. Female brown bears become sexually mature between 5 and 7 years of age, males usually will not mate until a few years later when they are able to compete successfully with other males for an available female.
Through a remarkable process known as delayed implantation, a fertilized egg will divide and float free within the uterus for six months. During hibernation, the embryo will attach itself to the uterine wall and the cubs will be born after an eight-week period while the mother sleeps (January or February). This process is important to the survival of the mother. Should she not gain enough weight to carry her through the winter, the embryo will not implant and be reabsorbed by the body.
The average number of cubs born is between one and four, with two being the average. There have been cases where a bear has been spotted with five cubs, though the mother has been suspected of adopting an orphan, which is not unusual. Age, geographic location and food supply influence the size of a bears litter. The number of cubs a female will have increases, as she gets older. At birth, the cubs are blind, toothless, hairless and very tiny weighing less than 1 pound. They feed on motherís milk until spring, when she is ready to leave the den, sometime between April and May and as late as June depending on climate conditions. At this time they will have developed enough to follow her and begin to forage. The cubs will weigh from 15 to 20 pounds at this time.
Cubs will stay with their mother from two to four years. During this time, they will learn survival techniques crucial to their existence. They will learn which foods return the highest nutritional values, where to attain them, how to hunt, how to fish, how to defend themselves and where to den. The cubs learn by following and imitating their motherís actions during the period they are with her.