Grizzly bear consumption of midges in Yellowstone National Park

Abstract Grizzly bears (Ursus arctos) are omnivore generalists that eat a wide array of plants and animals, including insects. Human-induced changes in climate may affect the species composition, abundance, range, and elevational distribution of the plants and animals consumed by grizzly bears. Therefore, determining the current food habits of grizzly bears is important for documenting future changes in food resources and how those changes may affect the nutritional ecology of grizzlies. In 2011, we observed grizzly bears in Yellowstone National Park (YNP) eating midges from the family Chironomidae along the shoreline of Yellowstone Lake. Midges are small, swarming aquatic insects that occasionally wash ashore in large numbers around the lake. To our knowledge, grizzly bear consumption of midges had not previously been reported in YNP despite extensive bear food-habits studies conducted there. We believe that midges are likely an opportunistic food for grizzlies, eaten only during sporadic periods of super-abundance.