Photo credit Frank T. van Manen/IGBST
What do grizzly bears eat?
The grizzly bear, like its cousin the black bear, is omnivorous, meaning it will eat plants, as well as insects and other animals. Scavengers by nature, grizzlies spend most of their waking hours searching for food. Forbs, roots, tubers, grasses, berries and other vegetation, and insects comprise most of the bear’s diet. But grizzlies are very adaptable, finding and subsisting on a variety of foods if necessary. The grizzly diet can include small rodents, fish, carrion, and even garbage and human food if it is easily available.
Food sources vary in availability from year to year, and from season to season. Grizzlies move throughout their habitat looking for foods available at that time of year. The availability of many foods is known to the bears by season, and the bears move to these areas based on their experience. In this way, the general seasonal distribution and movements of bears are predictable. Ingestion of large amounts of food in a short time period is critical to grizzly survival, since they are only active and feeding for 6-8 months of every year.
How will the supply of Whitebark pine nuts affect grizzlies in Yellowstone?
While whitebark pine cone seeds (also called pine nuts) provide a favorite grizzly bear food in the Yellowstone area, there are plenty of other food sources available to sustain this growing population during years of limited whitebark pine cone seeds.
U.S. Forest Service Whitebark Pine Program
Based on growing concerns of the health of whitebark pine ecosystems in Oregon and Washington, the PNW Genetic Resource Program began work in the early 1990’s with the PNW Forest Health Protection Program, USDI National Parks and others to gather information on the status of whitebark pine in Oregon and Washington. Early work included an informal information survey, seed collections to be used to examine natural genetic resistance to white pine blister rust and common garden studies to examine genetic variation, germination tests to examine longevity of seed in cold storage and germination procedures, protocols to grow whitebark pine seedlings, and surveys of the health of whitebark pine ecosystems. Beginning in 2004, this work has intensified and a four year ‘Pacific Northwest Albicaulis Project’ was initiated.
- View the rest of the article at the USDA Forest Service website.
- Read or download the report “Response of Yellowstone Grizzly Bears to Changes in Food Resources: A Synthesis” (2013)
Wildfires and Grizzly Bears
Written by U.S. Fish and Wildlife Service
Grizzly bears have lived with wildfire for as long as they have roamed the Earth and have adapted to living with fire for thousands of years. Wildfires typically create mosaic patterns of burned and unburned vegetation; because bears are highly mobile and opportunistic, they move to the unburned areas in search of food and cover. The overall long-term impact of forest fire as a natural process is that it increases diversity of habitats and maintains resilience and vigor in ecosystems, which is beneficial to grizzly bears.
While some sources of food and cover may be removed by fire in the short-term, bears quickly return to burned areas in search of carrion from animals killed by the fire. They also forage on lush revegetation of grasses and forbs, which occurs quickly, aided by a flush of nutrients recycled to the soil. As dead trees fall to the ground, they provide habitat for ants and other insects, another important component of the grizzly bear’s diet. Within 3-7 years or more after the fire, berry-producing shrubs begin producing a crop again; grizzlies that have moved to unburned portions of their home range to forage on berries in late summer and fall then return to this renewed food source in burned areas. If whitebark pine stands are burned, there will be an immediate decrease in the availability of pine nuts; bears may move to new areas in the fall, searching for alternate foods, which may result in increased encounters with humans. However, the long-term effect of fire is positive for bears, because it increases ecosystem diversity and creates a greater variety of bear foods over time.