Seasonal variation in female Asian elephant social structure in Nagarahole-Bandipur, southern India

Abstract

Fission–fusion dynamics allow for individuals to deal with spatiotemporally changing food resources, with groups from a community fusing together when resources are abundant and splitting away when competition for resources is high. Such fission–fusion dynamics are often modulated by seasonal changes in resources. We examined the seasonal variation in group size and social structure of female Asian elephants, which show high fission–fusion dynamics, in a population in southern India. Females in this population form many distinct communities or clans in both the dry and wet seasons. At the population level, females were sighted in larger group sizes and associated with more uncommon females in the dry season. However, when associations among common females were considered, a greater number of stronger associations were observed in the wet season. There were no consistently significant seasonal differences in group sizes or associations at the clan level. Thus, population-level results, obtained by a combination of results from different clans, may sometimes be misleading. Female associations showed some temporal stability, with association indices being moderately correlated across consecutive seasons and years. Interestingly, average group sizes were similar across clans of different sizes, indicating a restriction on group size, possibly due to resource distribution. In spite of this restriction, most clan-mates showed low, non-zero associations amongst themselves rather than very strong associations with a small set of individuals. The resulting fluid rather than fixed groups suggest a benefit to socializing with other clan-mates. Thus, unlike the pattern usually seen, fission–fusion dynamics here is a means to maintain multiple associates under conditions of relatively constant but constrained group size, rather than being a means of increasing or decreasing group size in response to ecological factors.