Monitoring Ungulate Carcasses and Grizzly Bear Scavenging on the Northern Yellowstone Winter Range

Abstract

Ungulate carcasses are an important food source for scavengers, including, grizzly bears (Ursus arctos horribilis), in the Greater Yellowstone Eosystem. Each spring since 1989, nine transect routes in the Gardiner Basin, Montana, have been used to monitor availability of ungulate carcasses. We surveyed these transects during March-May 2006 and also conducted a complete search for carcasses on important parts of the Northern Yellowstone Winter Range (NYWR) adjacent to Yellowstone National Park (YNP). Our goals were to determine 1) how counts of ungulate carcasses on existing transects compared with more complete carcass counts along transects throughout the landscape and 2) document bear scavenging on the carcasse. Carcass density on existing transects was four times greater than on new transects, 0.8 vs. 0.2 carcasses/km, respectively. The original transects included areas where carcasses were most likely to be found and provided a good annual index of ungulate carcass availability. Starvation was the cause of death for 70 percent of recorded ungulates (11 = 106). Contrary to findings inside YNP. We found very little evidence of grizzly bear predation or use of carcasses (1 of 106 carcasses) or total bear use (4 carcasses) in the Gardiner Basin. This may be due to a greater level of human disturbance or a lower density of bears on National Forest winter range compared to YNP winter range.