Oconto Falls

Reproduction

The sexes coexist briefly during the mating season, which generally peaks from June to mid-July. Females remain in estrus throughout the season until they mate. They usually give birth every other year, but sometimes wait 3 or 4 years. Pregnancy generally lasts about 220 days, but this includes a delayed implantation. The fertilized eggs are not implanted in the uterus until the autumn, and embryonic development occurs only in the last 10 weeks of pregnancy. Births occur mainly in January and February, commonly while the female is hibernating. The number of young per litter ranges from one to five and is usually two or three. At birth the young weigh 200 to 450 grams each, the smallest young relative to adult size of any placental mammal. They are born naked and blind. Black bear cubs remain in the den with their torpid mother and nurse throughout the winter. When the family emerges in the spring the cubs weigh between 2 and 5 kg. They are ususally weaned at around 6 to 8 months of age, but remain with the mother and den with her during their second winter of life, until they are about 17 months old. At this time the female is coming into estrus and forces the young out of her territory. They may weigh between 7 and 49 kg at this point, depending on food supplies.

Dewey, T. and C. Kronk. 2007. "Ursus americanus" (On-line), Animal Diversity Web. Accessed February 14, 2009 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Ursus_americanus.html.