:We analysed the behaviour of muskox herds during early winter (October–November), late winter (April–late May), and early spring (late May–early June) in relation to diet quality, snow and forage abundance, and daylength. Muskoxen exhibited distinct cycles of activity and lying. The duration of activity periods, as determined by time series analysis, showed no relationship to snow thickness at feeding craters, graminoid abundance, nor diet quality. The duration of lying periods was inversely correlated to forage quality, as indexed by fecal nitrogen, and was positively correlated to snow thickness, but these relationships were confounded by concurrent changes in daylength. Lying was the dominant activity during all seasons. Principal components analysis of time budgets revealed that feeding activity increased during spring largely at the expense of lying. Muskoxen exhibited a low of activity near mid–day during all seasons. We discuss some methodological issues in the analysis of time budgets and activity cycles of social groups.