See the bear before you surprise it. Watch for fresh tracks, scat, and feeding sites (diggings, rolled rocks, torn up logs, ripped open ant hills).
Avoid Hiking Alone
Whenever possible hike in groups of three or more people—91% of the people injured by bears in Yellowstone since 1970 were hiking alone or with only one hiking partner; only 9% of the people injured by bears were in groups of three or more people.
Avoid Hiking at Dawn, Dusk, or at Night
Whenever possible avoid hiking at dawn, dusk, or at night. During the hot summer season these are the periods when grizzly bears are most active.
Don't Expect Bears to Notice You First
In Yellowstone National park bears hibernate for approximately 5 months each year and have only 7 months of active time to obtain all of their nutritional needs. Therefore a bear with its head down feeding may not see you as you as quickly as you would think. Pay attention and see the bear before it sees you and before you surprise it.
Make Noise, Alert Bears to Your Presence
When hiking, periodically yell "Hey Bear" especially when walking through dense vegetation or blind spots, or when traveling upwind, near loud streams, or on windy days. Avoid thick brush whenever possible.
Bears will guard and defend carcasses against other scavengers or humans. Dead ungulates will attract and hold many bears near the carcass site. It is risky to approach a carcass; many bears may be bedded nearby just out of sight. If you find a fresh dead ungulate carcass that still has a lot of meat remaining, leave the immediate area by the same route you approached the carcass from. Report all carcasses to the nearest ranger station or visitor center.
Stay With Your Gear
DO NOT RUN
Don't leave your packs, lunches, food, or beverages unattended as they may attract and hold bears at the site. If you surprise a bear that's eating your stashed food you may lose more than your lunch.