Black bears breed from May through August, with most activity peaking in June and July. Adults are solitary, and during the summer months males travel over large areas to enhance their chances for encountering mates.
Although males become sexually mature at 1-2 years of age, most do not participate in breeding until they have reached full adult size, at about 4-6 years in Maine.
Females in Maine become sexually mature at 3-5 years of age. Individual females have a 2-year reproductive cycle, which is related to their long period of parental care for cubs.
Bears have a long gestation period, but most fetal development is delayed until the final 6-8 weeks. Breeding occurs in the summer, prior to the fall feeding period that provides the female with stored body fat to supply demands for fetal development and her survival during the winter. If a female is unable to store sufficient body fat, the pregnancy is terminated.
Most fetal development occurs in early winter, after the female has entered a den, and 1-4 cubs are born inside the winter den during January – February. Cubs weight about 12 ounces at birth, and depend on their mother for warmth and nutrition during the remainder of the winter. They grow to 4-10 pounds by mid-late April, when the mother leads them away from the den.
The family group remains together for 16-18 months, until the female reenters estrus and disperses her yearlings as another breeding season begins.
In northern Maine, fluctuating beechnut crops have produced alternating years of high and low cub production, with most cubs being born on odd-numbered years. Cub production is more consistent in central Maine, where more stable fall food supplies result in nearly half of adult females giving birth each year.
Bears are long-lived animals, capable of surviving 30 years in the wild. Their survival increases as they mature. Nearly half of newborn cubs may die before reaching their first birthday, with starvation being a major cause of death. By the time bears in Maine reach 2 years of age their survival exceeds 90%, and nearly all deaths of adult bears are due to hunting or other man-related causes.
by Craig McLaughlin, Ph.D.
Maine Inland Fisheries and Wildlife