SOCIAL-ORGANIZATION IN A WILD POPULATION OF CALLITHRIX-JACCHUS .1. GROUP COMPOSITION AND DYNAMICS

Data are presented on group dynamics in a wild population of the commo n marmoset, Callithrix jacchus, in northeastern Brazil. Three marked a nd habituated groups were observed, and composition noted, for at leas t 5 days a month over 12-18 consecutive months. Group sizes ranged fro m 5 to 15 individuals, and changes in group composition were the resul t of births, emigrations, and disappearances. No immigrations into the main study groups were observed throughout the study period. None of the three known emigrants was known to join an established or incipien t group for up to 10 weeks after their departure. One group contained only breeding individuals and their offspring. Observations of recruit ment and loss in the other two groups suggest that they, too, were ext ended family groups. The group dynamics described in studies of other populations of Callithrix suggest that extended family groups, or at l east groups consisting of breeding individuals and their close relativ es, may be characteristic of those populations.