Bear Foods Monitoring

Elk, bison, cutthroat trout (Onchorynchus clarkii), and whitebark pine (Pinus albicaulis) seeds are four of the highest sources of energy available to grizzly bears in Yellowstone National Park. Due to the importance of these foods to bears, park staff monitor their annual availability within the park.  

Carcass Surveys
To determine how much ungulate carrion is available for bears to scavenge after leaving their dens, the northern ungulate winter range and three areas of thermally influenced winter range in the park’s interior are surveyed each year between April and early May. The surveys are conducted on up to 28 routes that cover a linear distance of about 350 km; however, one or more routes must frequently be omitted because of closures for wolf denning or recent snowfall. Survey routes are hiked, snowshoed, or skied by teams of at least two people. Data are collected on all ungulate carcasses, bears, and bear sign (tracks, scat, feeding sign) that are observed from the survey routes. Carcass information includes data about the animal (i.e., species, age, sex, evidence of cause of death), the site (UTM location, aspect, slope, elevation, distance to road, distance to forest edge), and any evidence of predation or scavenging. Since 1997, the average number of carcasses found per 10 kilometers of survey range has been slightly less than two on the northern range, and slightly more than two in thermally influenced areas. Competition with wolves for carrion and changes in bison and elk management policies in the GYE may affect carcass availability and use by grizzly bears. It may also be possible to relate changes in ungulate carcass numbers to factors affecting elk winter-kill such as weather, winter severity, and forage availability.

Spawning Stream Surveys
To determine the availability of spawning cutthroat trout to bears in backcountry and frontcountry streams, park staff conduct weekly surveys on the Trout Lake inlet and 12 Yellowstone Lake tributaries during the spawning season. For each survey at each site, two people walk upstream from the stream mouth and record the number of adult trout observed. The number of fish counted during the peak week is used to identify annual trends. Evidence of bear activity is also recorded. Bear activity at Yellowstone Lake spawning streams has declined dramatically since 1989, presumably in response to the decline in spawning Yellowstone cutthroat trout. Additional Information (PDF)  

Whitebark Pine Surveys
To determine the availability of whitebark pine seeds to bears, whitebark pine cones are counted each fall on 19 transects within the GYE, 10 of them within YNP. Tree mortality resulting from mountain pine beetle infestation has been high in GYE transects in recent years. Overall, approximately 8% of whitebark pine stands in YNP have been affected by pine beetle activity; 37 of the 100 transect trees that were alive in 2002 were dead by 2004.    

Additional project information and Annual Reports are available at the Official Yellowstone National Park Website: Bears and the Interagency Grizzly Bear Study Team Website.