Habitat Preference and Forage Consumption by Reindeer and Caribou near Atkasook, Alaska

Abstract

Habitat preference by caribou (R. tarandus grantii Allen.) and forage selection and consumption by tame reindeer (R. tarandus tarandus L.) were studied near Atkasook, Alaska, for 3 yr. Small groups of caribou were present in both winter and summer. Winter habitat use was associated with elevated areas with high lichen biomass, while summer habitat use was associated with landform units high in deciduous shrubs or lichens, e.g., upland tussock tundra, ridges and lake margins. These observations, and measurements of forage availability and digestibility, indicated that caribou preferred habitats that provided high availability of digestible forage. Intensive grazing studies with reindeer on several vegetation types indicated a high preference for forbs, deciduous shrubs (Salix spp.) and lichens. In high-center polygons, preference was shown for microhabitat units with high plant species diversity, i.e., wet, shallow troughs. Reindeer tethered on lake margin vegetation showed high preference for the willow strings. Selection of food by reindeer appeared to be related to plant availability, nutrient content, digestibility and secondary compounds. Forage consumed by reindeer was 10% higher in digestibility than was the available herbage. In 3 days of grazing on a 314 m2 study site a single reindeer consumed less than 10% of the aboveground standing crop, but standing declined over 30% due to excess clipping and trampling. Estimated daily dry matter intake was high when reindeer were feeding on landform units high in deciduous shrubs. When reindeer grazed exclusively on Salix pulchra a 30% increase in rumen turnover time was noted, which suggests a decline in food intake. Food intake also declined markedly over a 3 day grazing period as forage availability declined. The projected seasonal trends in dry matter, digestible dry matter, N, P and Ca intake of reindeer at Atkasook were compared with those projected for wet, coastal tundra at Prudhoe Bay. The inland tundra generally allows greater production of reindeer.