Distribution of grizzly bears in the Greater Yellowstone Ecosystem, 2004

The US Fish and Wildlife Service (USFWS) proposed delisting the Yellowstone grizzly bear (Ursus arctos horribilis) in November 2005. Part of that process required knowledge of the most current distribution of the species. Here, we update an earlier estimate of occupied range (1990–2000) with data through 2004. We used kernel estimators to develop distribution maps of occupied habitats based on initial sightings of unduplicated females (n = 481) with cubs of the year, locations of radiomarked bears (n = 170), and spatially unique locations of conflicts, confrontations, and mortalities (n = 1,075). Although each data set was constrained by potential sampling bias, together they provided insight into areas in the Greater Yellowstone Ecosystem (GYE) currently occupied by grizzly bears. The current distribution of 37,258 km² (1990–2004) extends beyond the distribution map generated with data from 1990–2000 (34,416 km² ). Range expansion is particularly evident in parts of the Caribou–Targhee National Forest in Idaho and north of Spanish Peaks on the Gallatin National Forest in Montana.