Bears are omnivores that have relatively unspecialized digestive systems similar to those of carnivores. The primary difference is that bears have an elongated digestive tract, an adaptation that allows bears more efficient digestion of vegetation than other carnivores (Herrero 1985). Unlike ruminants, bears do not have a cecum and can only poorly digest the structural components of plants (Mealey 1975). To compensate for inefficient digestion of cellulose, bears maximize the quality of vegetal food items ingested, typically foraging for plants in phenological stages of highest nutrient availability and digestibility (Herrero 1985).

The food habits of grizzly bears in Yellowstone National Park have been described in detail by Knight et al. (1984). Overall, whitebark pine nuts, graminoids, and ungulates are the most important foods in the grizzly bear's diet. Grizzly bear food habits are influenced by seasonal variation in available foods.

Spring

From March through May, ungulates, mostly elk and bison, comprise a substantial portion of a grizzly bear's diet. Grizzly bears feed on ungulates primarily as winter-killed carrion but also through predation on elk calves. Other items consumed during spring include grasses and sedges, dandelion, clover, spring-beauty, horsetail, and ants. Grizzly bears also feed extensively on whitebark pine nuts stored in red squirrel caches, especially during springs when an abundance of pine nuts have been left over from the previous fall (Mattson and Jonkel 1990).

Summer

From June through August, grizzly bears continue to consume grasses and sedges, dandelion, clover, spring-beauty, whitebark pine nuts, horsetail, and ants. In addition, thistle, biscuitroot, fireweed, and moths are eaten. Predation on elk calves continues until late-June/early-July when grizzly bears are no longer able to catch calves (Gunther and Renkin 1990). In areas surrounding Yellowstone Lake, bears feed extensively on spawning cutthroat trout (Reinhart 1990). Starting around midsummer, grizzly bears begin feeding on strawberry, globe huckleberry, grouse whortleberry, and buffaloberry. By late summer, bistort and yampa are included in the diet, and grasses, sedges, and dandelion become less prominent.

Fall

From September through October, whitebark pine nuts are the most important bear food. Other items consumed during fall include: grasses and sedges, bistort, yampa, strawberry, globe huckleberry, grouse whortleberry, buffaloberry, clover, horsetail, dandelion, ungulates, ants, and moths.

* Information on this page provided by the NPS.