Bears feeding on a protein-rich food source show significant weight gains and enhanced fecundity. Spring, after the bears' emergence from winter dens, is a period of relative food scarcity. Bears tend to lose weight during this period and continue to subsist partly off of body fat stored during the preceding fall. As summer approaches, a variety of berry crops become available. 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 ususally two or three.