Group fusions and minimum group sizes in vervet monkeys (Cercopithecus aethiops).

Six unequivocal cases of group fusion occurred between 1984 and 1988 in a declining population of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya. In each case, the remaining group members abandoned their territory and joined a neighboring group shortly after the group lost its penultimate adult. Because the number of juveniles did not appear to influence the timing of fusion, only adults (both males and females) appear able to maintain vervet groups as cohesive units. After examining the relative contributions of adults and juveniles to groupliving, we infer that intergroup competition may be more important than predation avoidance in determining the timing of fusions.