Usually, they live in groups of up to two hundred individuals. When a group's size reaches 80-100 members, a subgroup of females may split off to form a new group. Populations generally consist of a few unrelated males and many closely related females. Sometimes small groups form that consist of only males. Males usually leave the group in which they were born shortly after they reach sexual maturity.
Offspring born to a mother and son, or to siblings, are very rare.
Both males and females in a group show a preference for high ranking members of the opposite sex. Dominance hierarchies exist in both sexes of M. mulatta . This is far more evident in males, where competition for mates may occur regularly. The female members of a group usually live in complete harmony and rarely have violent interactions with one another. While M. mulatta live in groups, they are not territorial.