Cerococebus albigena: Site Attachment, Avoidance, and Intergroup Spacing

Abstract

Intergroup spacing of free-ranging mangabeys, Cercocebus albigena, was investigated by observation of group movements and intergroup behavioral interactions in western Uganda between 1971 and 1974. This omnivorous, arboreal species distinguishes itself from many other forest monkeys by its large home range and seminomadic pattern of movements. Although site attachment seems to be slight, its existence can be demonstrated by comparison of group movements with random-walk predictions. Frequency of intergroup encounter is extremely low; approaches involving visual contact between groups were observed only once in 120 days of systematic following. Interaction frequency can be compared with that predicted by a simple "gas" model of independent movement; encounters were found to be considerably rarer than expected. Simultaneous observation of neighboring groups' tracks indicates that groups tend to avoid each other by mutual withdrawal when they detect each other within about 500 m. Avoidance between groups is often accompanied by rapid approach and "monitoring" by certain adult males (christened RA males) which may interact directly with members of the opposing group but more commonly remain nearby but out of sight. Mutual avoidance occurs irrespective of the relative sizes of the interacting groups and of the location of the encounter relative to home-range centers. Existence of this avoidance-based spacing system may be favored by the irregular temporal distribution of major food resources, which has been documented in this study area. The relevance of the RA males' behavior to the maintenance of such a mutually reciprocal system is discussed.

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