Grizzly Bears and Forestry: Increased Mortality Leading to Lower Abundance in Heavily-roaded Landscapes

Extended Abstract: Both human-caused mortality and food are recognized to be the primary determinants of the distribution and abundance of grizzly bears (Ursus arctos); however, before our study, there was no information on the ecology of grizzly bears in the arctic watershed of central British Columbia (B.C.). From 1998 to 2002, we monitored habitat use and survival of 59 radio-collared grizzly bears (n = 37 females, n = 22 males) in an area surrounding the Parsnip River in central-eastern B.C. The 18,100-km2 study area encompassed a heavily timber-harvested plateau and an adjacent relatively pristine mountainous region. Thirty of the radio-collared bears were from the plateau (n = 19 females, n = 11 males); 29 (n = 18 females, n = 11 males) were from the mountainous region. We asked whether grizzly bears were less abundant in a heavily human-modified landscape (plateau) than in a relatively pristine landscape (mountains), and if so, why? A DNA population estimate concluded that mountain bears lived at a density of 49 bears per 1000 km2, while plateau bears lived at a density of 12 bears per 1000 km2 (Mowat et al., in press). This was a> 4-fold density difference between the two adjacent landscapes. Capture data indicated that adult plateau bears were heavier than adult mountain bears (spring captures: x