Male African elephants (Loxodonta africana) queue when the stakes are high

Linear dominance hierarchies are thought to form within groups of social animals to minimize conflict over access to resources. Dominance in both male and female African elephants (Loxodonta africana) is based mostly on intrinsic factors relating to age, and dominance hierarchies have been described within and between family groups of females. Very little is reported about male elephant social structure and dominance has only been described at the level of one-on-one contests. We test the hypothesis that male African elephants form linear hierarchies when resources are limited by monitoring a known group of elephants in Etosha National Park, Namibia, and measuring dominance interactions between males (outside the context of reproduction) during the dry season of 4 consecutive years. We show that males form a stable linear dominance hierarchy under normal arid conditions (in 2005 and 2007) when water is limited and resource competition is high. In unusually wet years with increased water availability (in 2006 and 2008), there is no linearity to the dominance hierarchy, less interaction between individuals and more agonistic behaviors exhibited, particularly in lower ranking individuals. This is the first study to quantify the existence of a linear dominance hierarchy in male African elephants as well as the effect of climatic fluctuations on dominance from year to year.