We investigated the behavioural mechanisms involved in group formation at a feeding site in a captive snowshoe hare population. The analysis showed that grouping resulted most often from a feeding attraction which led individuals to use the feeding site independently of each other. However social attraction and especially social repulsion among hares were also involved in group size dynamics. As group size increased, social repulsion underlined by an autocatalytic process led the hares to collectively leave the feeding site. Consequently, the social interactions rates and distance covered per hare increased non-linearly with hare number present at the feeding site. The results suggest that hare behaviour underlined by these mechanisms may influence the risks of starvation and predation. From these results, further field studies are suggested to test in the framework of a multi-factor hypothesis how hare behaviour, food supply and predation may interact simultaneously in population regulation.