Fission–fusion dynamics in wild giraffes may be driven by kinship, spatial overlap and individual social preferences

Many species exhibit fission-fusion dynamics, yet the factors that influence the frequent changes in group size and membership in these species have not been widely studied. Social ties may be influenced by kinship but animals may also form preferred associations because of social attraction or may only associate because they have similar habitat preferences. We investigated the association patterns of 535 wild giraffes, Giraffa camelopardalis, in Etosha National Park, Namibia using behavioural and genetic data from individually identified giraffes. We collected 726 records of group composition over a 14-month period and calculated pairwise association indices, which were tested against a null model. We found that female-female pairs, but not male-male pairs, showed both preferred and avoided relationships. We tested whether females' relationships could be explained by the degree of relatedness between pairs and whether pairs overlapped spatially. Correlations between matrices of pairwise associations, spatial overlap and relatedness showed that female-female associations were strongly correlated with amounts of spatial overlap and pairs that exhibited preferred relationships were more closely related than would be expected by chance. However, only about one-quarter of the variation in observed associations could be explained by spatial overlap and relatedness and therefore much of this variation may have been related to individual social preferences.