Skip to main content
Dryad

Data for: Environmental conditions alter behavioural organization and rhythmicity of a large Arctic ruminant across the annual cycle

Abstract

The existence and persistence of rhythmicity in animal activity during phases of environmental change is of interest in ecology and chronobiology. A wide diversity of biological rhythms in response to exogenous conditions and internal stimuli have been uncovered, especially for polar vertebrates. However, empirical data supporting circadian organization of large ruminating herbivores remains inconclusive. Using year-round tracking data of the largest Arctic ruminant, the muskox (Ovibos moschatus), we modelled rhythmicity as a function of behaviour and environmental conditions. Behavioural states were classified based on patterns in hourly movements, and incorporated within a periodicity analyses framework. We found that ultradian rhythmicity was prevalent when muskoxen were foraging and resting in mid-winter (continuous darkness). However, the probability of rhythmicity declined with increasing photoperiod until largely disrupted in mid-summer (continuous light). Individuals that remained rhythmic during mid-summer foraged in areas with lower plant productivity (NDVI) than arrhythmic individuals. We conclude that muskoxen may use internal time keeping when forage resources are low, but that the importance of this mechanism weakens once environmental conditions allow energetic reserves to be replenished. We argue that alimentary function and metabolic requirements are critical determinants of biological rhythmicity in muskoxen, which likely applies to ruminating herbivores in general.