Grizzlies are omnivores, which means they eat vegetation and meat. (Image credit: Nagel Photography/Shutterstock) Diet Most brown bears are most active during early morning and dusk.Ī grizzly bear in Yellowstone National Park, Wyoming. Grizzlies like to spend their days awake and hunting, but if humans are around they have been known to switch to a nightly schedule.

Hibernation lasts four to six months, which can add up to one-third to one-half of their life, according to the San Diego Zoo. Before hibernation, these bears will dig dens in hillsides and may line the floor with a bed of leaves. The fat in salmon help grizzlies bulk up for hibernation in the winter. When the salmon migrate upstream for the summer, grizzlies gather to catch their fill of these bountiful fish, according to National Geographic. The biggest gathering of grizzlies is during the salmon run in Alaska. One scientist who studied bears rubbing their backs in the woods says that by marking trees, male bears get to know one another better, thus reducing fighting among themselves over females. Rather, they are communicating with one another by leaving their scent.

Grizzlies have a habit of rubbing their backs against trees, but they're not trying to scratch an unbearable itch.

The long dark bear challenge map