Feeding rank in the Derby eland: lessons for management

Abstract

Transfers to new breeding herds and supplementary feeding are crucial management steps for small populations of ungulates. However, the successful realisation of those steps is strongly dependent on social interactions among individuals. Agonistic encounters connected with feeding determine the quality and quantity of the food accessed, and therefore directly influence food intake. We analysed the dominance relationships of mixed herds of critically endangered Western Derby eland with regard to access to supplementary food in the Bandia reserve, Senegal. We tested the influence of age and sex on feeding rank, the linearity and stability of hierarchies and the relationship between the position of an offspring in the hierarchy and the position of its mother. A linear hierarchy existed in all herds. Sex influenced the rank only in interaction with age. Feeding rank was significantly related to age in growing animals; in adults the effect of age was weaker. While body mass is correlated with age during the growth period and not after reaching adulthood, we concluded that the position in the hierarchy was related to the actual condition, reflecting the resource holding potential of individuals. The dominance index of a growing offspring depended on the index of its mother, but hierarchies of adult individuals were not stable. High-ranking individuals in good condition limited access to supplementary feeding to their lower-ranking herdmates. Effective supplementary feeding should therefore be provided in excess amounts to enable younger and weaker individuals in need to benefit from it, despite their lower positions in the hierarchy.

Keywords: dominance index, hierarchy, large herbivore, Taurotragus derbianus, ungulate, wildlife management