Hierarchical habitat selection by woodland caribou: its relationship to limiting factors

Habitat selection is a hierarchical process that may yield various patterns depending on the scales of investigation. We employed satellite radio-tele metry to examine patterns of habitat selection by female woodland caribou i n central Saskatchewan at both coarse (seasonal range) and fine (daily area ) scales. At each scale, we converted spatial data describing compositions of available and used habitat to standardised resource selection indices an d examined them with multivariate analyses of variance. Seasonal ranges gen erally showed preferential inclusion of peatlands and black spruce dominate d stands relative to recently disturbed stands and early seral stage forest s. In all populations, caribou preferred peatlands and black spruce forests to all other habitat types at the daily area scale. In general, these patt erns may reveal the effective avoidance of wolves, the primary factor limit ing caribou throughout the boreal forest. In three populations where season al ranges showed the selective inclusion of either young jack pine stands o r clearcuts along with peatlands and black spruce forests, we found a relat ive avoidance of the clearcuts and young jack Dine stands at the daily area scale. As all caribou populations in the area are thought to be relies of a once more continuous distribution, the seasonal range selection by animal s in disturbed areas may better describe historic rather than current habit at selection. We found inter-annual variation in selection at the coarser s patial scale in one population, and inter-seasonal variation in selection a t the finer spatial scale in three populations, indicating that the relativ e grains of the spatial and temporal scales coincide. We were better able t o explain the seasonal variations in finer scale selection by considering a vailable forage, a factor less likely than predation to limit woodland cari bou populations. The data agree with the theory that the spatial and tempor al hierarchy of habitat selection reflects the hierarchy of factors potenti ally limiting individual fitness.