Spatial overlap of Dall sheep, grizzly bears and wolves in the Richardson Mountains, Canada

Abstract

Dall sheep (Ovis dalli dalli) in the northern Richardson Mountains, Canada, are at the northeastern limit of the species range, and have been declining since the mid 1990s. Factors that may have contributed to the decline include: severe climate, density-dependence, interspecific competition, diseases, harvest, and predation. In this study, we investigate the indirect effects of predation by grizzly bears (Ursus arctos) and wolves (Canis lupus) on this Dall sheep population through the study of their spatial dynamics, in particular the overlap of the species composite home ranges. Between 2006 and 2009, we tracked individuals of the three species with GPS telemetry to describe their home ranges, movements and habitat use. Species composite home ranges revealed substantial overlap between areas used by all three species. The home range of wolves overlapped most of the Dall sheep range. When focusing on the core areas used by Dall sheep, however, the overlap with grizzly bears was larger. This suggests that wolves are likely encountered more often over a wider area whereas grizzly bear encounters are more likely in core areas. To refine our assessment of grizzly bear and wolf predation risk on this Dall sheep population, further analyses on individual and seasonal home range overlap, comparative habitat use, dynamics interactions, Dall sheep vigilance behaviour, predator diet and documentation of traditional ecological knowledge are required.