The ecology of woodland caribou in central Saskatchewan

Abstract

Habitat selection has been described as a hierarchical process that may yield various patterns depending on the spatial and temporal scales of investigation. I employed forest cover data and animal locations obtained through satellite radio-telemetry to examine patterns of habitat selection by female woodland caribou (Rangifer tarandus caribou) in central Saskatchewan. I began with random sampling of various types of forest stands focused on vegetation strata shown elsewhere to be of importance to woodland caribou. Cluster analysis and ordination by nonmetric multidimensional scaling suggested that six vegetation community types be recognized. Canonical correspondence analysis revealed strong relationships between the vegetation communities and data on canopy characteristics contained in the provincial forest inventory. Woodland caribou in Saskatchewan are now aggregated into several spatially disjunct populations. With regard to reproduction, first conception by females occurred at 16 months; the overall pregnancy rate was 94%; and the minimum parturition rate was 86%, all of which indicate adequate nutrition. The annual survival rate of adults was 84%, which is comparatively low, Calf recruitment was also low (28 calves: 100 cows), which I suspect was due to predation. Wolves (Canis lupus) have long been thought to limit woodland caribou populations while subsisting on other ungulate prey, but I speculate that black bear (Ursus americanus) predation may be an important cause of poor calf survival. My habitat selection work was conducted at both coarse (seasonal range) and finer (daily area) scales. Female caribou selected peatlands and black spruce dominated stands over recently disturbed stands and early seral stage forests in all five populations studied. This pattern may reveal the effective avoidance of wolves, the primary factor limiting caribou throughout the boreal forest. In three populations where coarse level selection suggested a relative preference of young forest stands or clearcuts, I found a reversal in selection patterns in finer scale selection. I interpret this to indicate that these populations are relics of a once more continuous distribution, and that their coarse level selection best describes historic rather than current selection. I determined that the hierarchy of habitat selection reflected the hierarchy of factors actually or potentially limiting caribou populations.