Social Structure Among Vervet Monkeys (Cercopithecus Aethiops)

The social structure of vervet monkeys (Cercopithecus aethiops) is described on the basis of a one year field study in the Masai-Amboseli Game Reserve of south-central Kenya, East Africa. The major findings and conclusions are as follows: 1. They lived in relatively stable and closed heterosexual groups, ranging in size from 7 to 53 with a mean of 24 individuals. The sex ratio in these groups was about 1 : 1. 2. Home ranges of the groups varied in size from 0.071 to 0.37 square miles. Group territories varied from 0.067 to 0.30 square miles. There was no obvious correlation between group size and home range or territory size. 3. Some groups intruded into foreign territories significantly more than expected by chance. 4. Certain territorial boundaries were extremely stable, whereas others oscillated back and forth over a distance as great as 240 yards. 5. Although the groups were relatively closed, enough intergroup transfers were seen to permit concluding that extensive inbreeding was avoided. 6. Dominance among vervet monkeys was expressed in terms of priority to spatial positions, food, and grooming relationships, and through aggressiveness in agonistic encounters. Intragroup dominance relations demonstrated a strong trend toward a determined and linear relationship. 7. Several correlates of dominance were found, including : role in the Red, White, and Blue Display; unassisted defense of the territory; and copulation. 8. Many coalitions associated with agonistic encounters were formed through preferences of the monkeys. 9. Recipients of coalitions were of two types: dominant antagonists or subordinant non-antagonists. 10. Some of the coalitions had a temporary effect on dyadic dominance relations, either neutralizing or reversing them. 11. Group progressions were led by certain individuals. Leadership of progressions seemed primarily related to age and secondarily to dominance. 12. Each group regularly divided into sleeping subgroups at sunset, rejoining after sunrise. These subgroups were not formed at random but were formed, at least partly, with reference to mother-infant, coalitionary, and dominance relations. Formation of sleeping subgroups probably facilitated the concealment of vervets from nocturnal predators. 13. Territoriality and dominance are discussed in the light of DAVIS' hypothesis and the relative importance of spatial parameters. 14. Vervet territoriality was characterized by all-purpose areas that were defended by all age-sex classes of heterosexual groups throughout the year (excepting infants). Territoriality of this nature is uncommon among mammals, examples being found only among Primates and Rodentia. 15. The adaptiveness of vervet social structure is discussed.