The timing of fission among free‐ranging rhesus monkeys

Behavioral observations were carried out on a large group of free‐ranging rhesus monkeys ( Macaca mulatta ) on Cayo Santiago from January 1968 to December 1969 and from October through December 1970. During this period, social group A divided. The 24‐month study period can be classified into five stages which represent the different phases in the process of group fission. Two criteria for fission were established: the cessation of grooming between adult females of different sub‐groups of the main group and the stabilization of the adult female population. The criteria were based on established information on group dynamics and inter‐group behavior on Cayo Santiago. Several points became clear from the chronological analysis. Group fission is a long process. The duration of the process of fission and the specification of the season in which fission begins and is completed depends upon the definition applied. For purposes of this analysis, fission was defined as beginning with the onset of spatial fragmentation and corresponded to the initial part of the breeding season. The fission was completed during the breeding season. The duration of the process of fission was 18 months.