Seasonal changes in social networks of giraffes

Fission-fusion social societies allow animals to respond in a flexible manner to environmental changes by adapting the size and composition of a group. Although group members change frequently in these systems, associations with preferred partners may be found. In this study, we examined the grouping patterns of a population of 80 individual giraffes in a fenced South African game reserve over a 12-month period. Using social network analyses as a tool to evaluate observed associations, we subsequently analysed both sex- and season-related grouping patterns within the study population. Mixed sex groups represented 49% of all groups observed, and although overall group composition distribution did not differ significantly between seasons, the number of encountered single females decreased by 50%, whereas the number of multi-male groups increased by over 50% in winter. Overall average group size did not differ significantly between seasons, but significantly larger multi-female and multi-male groups were seen in winter. Within the social network, two distinct clusters were found in summer, with the population more divided in winter, with five distinct clusters emerging. The strongest ties (highest HWIGs) were found between adult females. Our study revealed that giraffes not only live in a highly flexible social fission-fusion system, but also show seasonal patterns of grouping.