Range shift and winter foraging ecology of a population of Arctic tundra caribou

Some researchers have suggested that over periods of several decades, Arcti c tundra caribou (Rangifer tarandus) may be regulated by density-dependent forage depletion. Winter range shifts could potentially delay such regulati on when a population is at or near long-term maximum abundance. In the 1980 s, Inuit correctly predicted the mass emigration of caribou from a traditio nal winter range on Foxe Peninsula (FP) on southern Baffin Island, Nunavut, Canada. Most FP caribou subsequently emigrated to a new winter range on Me ta Incognita Peninsula (MIP). To determine if MIP provided emigrating carib ou with better foraging habitats, we compared winter forage resources and s now cover at caribou foraging sites, and food selection by caribou on FP an d MIP in April 1992. Caribou that remained on FP dug feeding craters in sha llower, softer snow than those on MIP did. Biomass of most fruticose lichen s was greater within foraging sites on MIP than on FP. Biomass of shrubs, o ther than Cassiope tetragona and Dryas integrifolia, was also greater on MI P than on FP. Dryas integrifolia was the only plant class that had higher b iomass on FP than on MIP. Cladina spp. / Cladonia spp., Sphaerophorus fragi lis, and Cetraria nivalis occurred less frequently in the rumens of FP cari bou. Proportions of fruticose lichens in rumens of caribou on both peninsul as were similar to those on other overgrazed and High Arctic tundra winter ranges. Caribou on FP showed a higher preference for the shrub C. tetragona . Biomasses of plants sensitive to long-term feeding or trampling by caribo u (i.e., the five most common fruticose lichens, other shrubs, and plant de bris) were consistently lower on FP, which is congruous with Inuit reports that long-term cumulative overgrazing had reduced the supply of important f orage plants on FP sites that were accessible to caribou in winter. FP cari bou that emigrated to MIP gained access to more abundant, higher quality fo rage resources than those that remained on FP. Because most FP caribou had emigrated, this South Baffin subpopulation escaped, at least temporarily, t he regulating effects of historical cumulative overgrazing.