Foraging Ecology And Sociality Of Muskoxen In Northwestern Alaska

Abstract

I investigated sociality and winter foraging ecology of muskoxen ( Ovibos moschatus) in Cape Krusenstern National Monument, northwestern Alaska. The nutritional value of moss (Hylocomium splendens, Tomenthypnum nitens) for muskoxen was evaluated by incubating moss in rumen-fistulated muskoxen and simulating post-ruminal digestion by incubation in acid-pepsin. Moss was indigestible in muskoxen and gained mass and nitrogen in the rumen. Consequently, high moss consumption during winter may result in net loss of nitrogen from a muskoxen's system. Local and regional differences in moss use by muskoxen and caribou or reindeer (Rangifer tarandus) were investigated in northwestern Alaska in relation to indicators of winter range quality. On muskox winter ranges, increases in fecal moss indicated decreased graminoid cover, harder snow, increased moss cover, and greater animal densities. Higher mobility of caribou than muskoxen during winter limits use of their feces to reflect local forage selection, but fecal moss may indicate caribou winter range quality on a larger, regional scale. Increasing proportions of moss in muskoxen feces may alert wildlife managers to shifts in forage availability due to changing snow conditions. Roles of male and female muskoxen in coordinating group movements were investigated during the snow-free season. Adult females led most activity initiations, foraging-bout movements, and spontaneous group movements. Rutting males actively manipulated female-led movements through herding and blocking. Leaders incurred no costs in terms of lost foraging time. Habitat use by muskoxen shifted from upland habitats in early summer towards lowland sedge meadows during rut. Muskox group sizes decreased from winter to summer to rut. Muskoxen foraging efficiency decreased with group size in spatially unlimited but not in spatially limited habitats. Adult males contributed least to group cohesion, and their presence may contribute to group fission during rut. A conceptual model is presented which discusses how habitat, foraging, social behavior, and predation threat contribute to group sizes, fission and fusion of muskox groups. Results from this study indicate that winter ranges used by muskoxen in Cape Krusenstern may be limiting, which suggests that numbers of muskoxen in this area will likely remain small. Therefore, hunting quotas should be low and limited to males only.