Contextual Factors Meditating Contests Between Male Chacma Baboons in Botswana: Effects of Food, Friends and Females

Abstract

We examined aggressive displays among male chacma baboons (Papio ursinus) over a 23-mo period in the Okavango Delta of Botswana. High-ranking males were more likely than middle- or low-ranking males to participate in displays. Regardless of rank, all males were more likely to participate in chases or physical fights if their opponent’s rank was similar to their own. Most chases and fights, including those that led to injuries, were also between similarly-ranked males. The rate of both aggressive displays and approachretreat interactions increased in the weeks before rank reversals, suggesting that rank challenges were preceded by a period when males assessed each others’ competitive ability and/or motivation. Aggressive displays between disparately-ranked opponents occurred most frequently in contests involving resources of high fitness value: the defense of meat, the defense of estrous females, and the protection of infants against infanticidal attacks. Silent displays were more likely to occur in these three contexts than were displays that occurred as part of more slowly escalating interactions, in which opponents first exchanged calls. Results suggest that competitive encounters among male baboons follow patterns predicted by evolutionary game theory.