Sex, age, and seasonal variation in the foraging dynamics of muskoxen, Ovibos moschatus, in Greenland

Abstract

The relationship between resources (forage availability and quality) and the foraging dynamics of muskoxen, Ovibos moschatus, was studied in Angujaartorfiup Nunaa, western Greenland, during spring (calving, post calving), summer, autumn (rut), and midwinter. Muskoxen did select among vegetation types in all seasons but calving. During the postcalving period, summer, and rut, the vegetation types meadow, moist dwarf shrub heath, and grassland were preferred, whereas meadow, moist dwarf shrub heath, and steppe were selected during midwinter. The relative availability of graminoids in vegetation types did not correlate with selection of vegetation types. Seasonal patterns of daily feeding time were negatively correlated with forage quality, whereas no correlation with forage availability was found. Seasonal rumination times were negatively correlated with both availability and quality of forage. The length of rumination time is apparently not solely explained by variations in forage quality. Results presented here indicate that rumination time is also a behavioural strategy of muskoxen. Movement rates did not correlate with forage availability. During midwinter, muskoxen did not respond to low forage quality by increasing daily feeding time as was seen during calving. Instead, an energy-conserving strategy was observed, where a relatively larger proportion of time was allocated to resting, i.e., nonruminating. Bachelor herds and mixed herds differed in daily feeding time and habitat use during the prerutting and rutting season. Prior to the rutting season, muskox bulls increased energy intake to compensate for the subsequent allocation of time to reproductive activities. During the short arctic growing season, muskoxen in western Greenland decreased daily feeding time, whereas those in eastern Greenland increased feeding time. This difference in foraging dynamics is hypothesised to be a result of differences in biotic and abiotic constraints imposed on muskoxen in these two regions.