Food Habits of Grizzly Bears and Black Bears in the Yellowstone Ecoystem
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 Greater Yellowstone Ecosystem (GYE) have been described in detail by Knight et al. (1984) and Mattson et al. (1991). Overall, army cutworm moths, whitebark pine nuts, ungulates, and cutthroat trout are the highest quality food items available to grizzly bears in the GYE. These foods impart the greatest nutritive value in exchange for the least foraging effort (Craighead et al. 1995). Grizzly bear food habits are influenced by annual and seasonal variation in available foods.
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At peak summer levels, 3,500 employees work for Yellowstone National Park concessioners and about 800 work for the National Park Service.