A grizzly bear in the Greater Yellowstone Ecosystem forages on greens.

A grizzly bear in the Greater Yellowstone Ecosystem forages on greens in a meadow. A grizzly bear can weigh over 600 pounds, and owes that to being an opportunistic omnivore. The IGBST has documented that Yellowstone grizzly bears consume a wide variety of foods, ranging from herbaceous plants, tubers, berries, and nuts to animals, insects, and fungi. Their diets can shift on a daily, weekly, seasonal, and annual basis, which has so far enabled them to adapt to changing food supplies.