One-male groups and intergroup interactions of mountain baboons

Abstract

The behavioral ecology of mountain baboons, Papio ursinus,cuts across the traditional dichotomy between savannah and desert baboons, providing fresh opportunities to examine socioecological relationships. Mountain baboons were studied at a site where covariation in altitude and group size helps to clarify the influence of ecology on social behavior. One-male groups and lone males were regularly found in the highest-altitude zones. In encounters with multimale groups, a one-male group retreated; the group’s single male attacked his females, herding them far away from the multimale group. The male himself then approached and watched (and often loud-called at) this group. In a two-male group, the younger male herded the females, while the older sometimes defended the group. One-male groups did not show regular, stable aggregations, but two such groups seasonally coordinated their ranging “in tandem.” Ecological explanations for these behaviors and their relationship to the behavior of hamadryas baboons are evaluated, and a new theory of the origin of one-male groups in baboons is developed.