The musculature and bone structure of the hump are adaptations for digging and for attaining bursts of speed necessary for capture of moose or caribou for food. Color is not a reliable key in differentiating these bears because both species have many color phases. Black bears, for example, occur in many hues of brown, and even shades of blue and white. Brown bear colors range from dark brown through light blond. Bear weights vary depending on the time of year.
Bears weigh the least in the spring or early summer.
They gain weight rapidly during late summer and fall and are waddling fat just prior to denning. Females weigh half to three-quarters as much. Inland bears are usually smaller than coastal bears, probably because they do not have a readily available supply of protein-rich food, such as salmon, in their diet. Brown bears have been known to live 34 years in the wild, though this is rare. Usually, old males may reach 22 years.