Grizzly Bear-Cattle Interactions on Two Grazing Allotments in Northwest Wyoming

We determined cause of death for 182 cattle found dead on 2 adjacent public land grazing allotments in northwest Wyoming during 1994-96. Grizzly bears (Ursus arctos) killed fifty-one calves and 6 adults, representing 1.1% (mean) of the annual calf herd and 0.1% of the annual adult herd. An additional 0.9-1.8% of remaining calves were missing each year. Black bears (U. americanus), although present, were not implicated in cattle depredation. We believe that missing calves experienced depredation similar to discovered calves because the proportion killed by bears was similar for those equipped with mortality-sensing transmitters and unmarked calves (P = 0.73). Thus, estimated depredation equaled 78 calves or 1.3-2.2% of the annual calf herd. All observed depredation occurred at night (n = 9). Kills were separated by a mean of 3 days (n = 50) and occurred between 16 June and 13 September (median = 9 August). Radiotagged grizzly bears (n = 17) spent a greater proportion of time in the study area while depredations were occurring, and 10 were located near cattle more frequently than expected (P < 0.05), but most did not kill cattle. Although individuals from all sex and age (subadult, adult) groups except subadult males killed cattle, 3 adult males were responsible for 90% of confirmed losses. We employed management actions including euthanasia, translocation, and aversive conditioning to remove chronic depredators. No depredations were discovered following absence of the 3 depredating males in 1996, unlike the previous 2 years when losses continued for an additional 4 to 6 weeks. This suggests that removal of chronic depredators can reduce losses. Other bears did not become more depredatory, although many were known to utilize cattle carcasses. Removal of cattle carcasses during 1996 appeared to reduce bear densities but did not deter depredatory bear behavior. Identification and removal of depredatory individuals appears key in addressing conflicts with grizzly bears on rangelands.