Vegetation usually makes up 80 percent to 90 percent of a brown bear's diet. Brown bears eat green vegetation, including grass, leaves, wild fruits and berries, nuts, and below-ground bulbs and tubers of native plants. Because of the clearing of land for farming and the use of pesticides, there has been a decrease in the availability of green vegetation for brown bears. This has forced many to seek other forms of nutrition.
Insects are a popular snack for brown bears. Their favorites include termite nests, worms, ants and various species of beetle. The larvae of insects are an important source of protein, for which bears will overturn old trees and dig in the ground. Their large, long claws are ideal for scraping away bark to get to insects and their larvae. Army cutworm moths have become a more popular source of nutrition for brown bears living in areas where disease has affected the vegetation that they traditionally fed upon.
Meat makes up about 10 percent to 15 percent of the diet of the brown bear, mainly in the form of animal carcasses or carrion of large game animals. Brown bears are also known to feed on rodents, squirrels, foxes and other smaller animals. They sometimes prey on small game such as elk or moose calves, which they kill and then drag to their dens, to feed to their young or to sustain them through the winter.
Fish is a favorite food for bears, and they are skilled at retrieving live fish from the water. Mother bears teach their young how to fish in rivers and lakes. Brown bears native to Canada and Alaska traditionally eat salmon, a rich source of protein and oils. In Yellowstone National Park, brown bears feed on spawning trout, which are plentiful.
