Seasonal habitat use, habitat selection, and migratory behaviours of Stone’s sheep (Ovis dalli stonei) in northern British Columbia, Canada

Habitats and migration corridors used by wildlife have become increasingly modified by anthropogenic disturbances, and in many cases have resulted in population declines and local extirpations. To conserve ungulate populations, management strategies often focus on identifying and mitigating disturbances in critical habitats and seasonal ranges. The Cassiar Mountains of northern British Columbia, Canada are home to a spatially structured population of Stone’s sheep (Ovis dalli stonei) composed of small bands (groups) of sheep dispersed throughout the region. The Cassiar Mountains are largely unaltered by human land-use and disturbance, however, more recent increases in recreation and potential resource development expansions might threaten critical habitats and alter seasonal movements of the Cassiar population. My objectives in this study were to identify lambing events, estimate habitat selection during critical lambing and nursery periods, and examine the seasonal space-use and migratory patterns of 18 collared female Stone’s sheep to identify areas of high conservation priority. I assessed individual movement patterns and used vaginal implant transmitters to identify lambing events from 2018 to 2020. Females gave birth from May 3rd to June 14th, which was within the expected lambing season of northern mountain sheep. I estimated habitat selection during each female’s lambing and nursery periods at two spatial scales; first, at the home range scale, by fitting resource selection functions, and second, at a finer scale constrained by individual movement by modelling integrated step selection functions. I found habitat selection was consistent across scales. During lambing and nursery periods, females selected southwest slopes in rugged, steep terrain at mid elevations, demonstrating selection for landscape features that facilitate predator avoidance. Further, during the nursery period, females exhibited selection for intermediate greenness, and unexpectedly, for habitats near roads, likely due to nursing females accessing nutritionally important mineral licks adjacent to roads in the area. To evaluate the seasonal space-use and migration behaviours of Stone’s sheep, I estimated Brownian bridge movement models to delineate winter and summer ranges, migration corridors, and stopover sites. Next, I classified individual migration strategies based on seasonal geographic and altitudinal movements between summer and winter ranges. Variation in migration strategies did not occur across individuals, but rather across bands, suggesting migratory diversity in the Cassiar population is driven by the distribution of resources and topography within the local landscapes of different bands. Due to two bands crossing a major highway during spring and fall migrations, I recommend installing road signage and speed reductions near these areas to reduce road-strike mortality risk and potential impacts to connectivity. Further, I recommend mitigating disturbances in delineated migration corridors, seasonal ranges, and suitable lambing and nursery habitats to better conserve Stone’s sheep in the Cassiar Mountains.

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