FACULTATIVE EXPRESSION OF BEHAVIORAL-DIFFERENCES BETWEEN ONE-MALE AND MULTIMALE SAVANNA BABOON GROUPS

A one-male unit (OMU) of chacma baboons (Papio ursinus) in northern Botswana formed by the asymmetrical fissioning of a multimale (MM) group. During long-term (13 years) observations in this area, which has a relatively high density of baboons, we observed only MM groups with 6 or more adult males per group (N = 19). The behavioral repertoire of the OMU generated a pattern of sociality unrepresentative of these MM groups. Distinctive behavior patterns expressed by the male of the OMU included vigilance oriented away from the group and suppression of intragroup aggression among all other group members. There was also a difference between the foraging and movement patterns of the OMU and those of MM groups in environmentally similar or the same areas. The OMU moved and foraged in a cohesive formation and all group members often foraged in single fruiting trees. Under comparable circumstances at the same time and places MM groups foraged in dispersed formation. Diet and habitat choices of the OMU differed from those of neighboring groups. Patterns of sociality associated with OMUs have been interpreted as responses to extreme environmental conditions [Byrne et al.: Am J Primatol 20:313-329, 1990]. However, it is also possible that alternative behavior patterns are facultative tactical responses to social circumstances. The alternative social styles of OMUs arising within typically MM populations identify the breadth of the behavioral repertoire and the capacity for social flexibility within contemporary savanna baboon and perhaps other primate populations.