Sociality is environmentally and phylogenetically determined and can vary intraspecifically and interspecifically. We investigated the reasons for group living in the African ice rat Otomys sloggetti robertsi, a diurnal, herbivorous, non-hibernating murid rodent, endemic to the sub-alpine and alpine regions of the southern African Drakensberg and Maluti mountains. We expected ice rats to be group living, nesting communally in underground burrows. We documented the spatial organization and social behaviour of free-living ice rats through direct observations and experimental manipulations. Colonies comprised 4–17 adults of both sexes. Members of a colony had a high degree of spatial home-range overlap but no temporal overlap because interactions between members were rare aboveground. Individuals experimentally displaced within their own colony were attacked by members of their own colony and were treated in the same way as strangers from other colonies. Members of a colony competed aggressively for prized food, particularly in winter. Ice rats displayed a vertical spatial separation in social behaviour, from huddling and tolerance belowground to solitary foraging and mutual avoidance aboveground. Such a dichotomy in sociality reflects the compromise between the benefits of social thermoregulation and burrow sharing on the one hand and the constraints of competing for resources, mainly food, on the other. Such a compromise may ultimately be related to the poor physiological adaptation of ice rats to the cold environments they inhabit.