The influence of forage and parasites on the migration of the Dolphin-Union caribou herd

• Main Author: Hughes, Joelene R.
• Published: University of Aberdeen 2006
• Subjects: 599.6581568
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439970

This thesis investigated whether the change in migration pattern was linked to forage availability and considered two mechanisms by which the forage resource on Victoria Island may have been compromised. Examination of remote-sensed NDVI, an index of the biomass of vegetation in an area, at a landscape scale demonstrated that the mainland provides caribou with higher vegetation quantity. Other factors may also influence the ranging behaviour of individuals, for example the range shift also led to changes in diet, and thus quality of forage. At the time of the wintering range shift, the populations of both caribou and the sympatric Arctic ruminant, muskox (<i>Ovibos moschatus)</i>, were found to be increasing on Victoria Island. Availability of forage was therefore potentially decreasing, in particular due to the muskox who are resident on the south of the Island throughout the year. The impact of grazing on vegetation in different seasons was examined by carrying out an enclosure grazing experiment. Summer grazing by muskox significantly reduced vegetation biomass in areas likely to be used by caribou during the winter. Therefore the availability of wintering forage may have been reduced by increase in temporally separated forage competition, possibly stimulating the range shift. In addition to forage availability being directly impacted by grazing, the resource can also be indirectly affected by parasites. Food-borne parasites, such as gastrointestinal nematodes, may reduce nutrient assimilation, whilst other more active parasites, such as oestrid flies, may reduce feeding time and energy storage through harassing their hosts. The potential for increasing parasite burdens decreases the benefits of foraging in a particular area. High burdens of both these parasite groups were related to poor condition, as indicated by weight and reproductive state, in the Dolphin-Union caribou.