Milne-Edwards’s sifaka groups are female-dominated, with females winning the majority of male-female conflicts, although, in general, aggression rates are relatively low in this species. Female dominance is common in lemur species, but rarer among other primates.

Milne-Edwards’s sifakas exhibit an unusually flexible social system compared to many other primates. They might live in harems, multi-male/multi-female groups, male-female pairs, and single-female/multi-male groups. Even more remarkably, the same individuals may engage in different social systems each year. Researchers aren’t yet sure what causes the different social systems to form, although it’s possible that environmental factors, such as food availability, may have an influence. None of the different social systems appear to be more beneficial than the others for infant survival. Regardless of social system, groups tend to contain only a small number of juveniles and infants, often just one or two.

Upon reaching sexual maturity at around 3.5 years of age, males and females can either remain in their natal group or disperse to a new group. Consistent with the notion that dispersal is to prevent inbreeding, individuals seem to only remain to reproduce in their natal group when there is an unrelated member of the opposite sex. Individuals can delay dispersal from their natal group until they are 6 or 7 years of age.

When either males or females immigrate into a new group, it is common for them to commit infanticide—that is, to kill existing infants in their new group. Infanticide by males brings females into estrus quicker so that the immigrating male can produce his own offspring with the resident female(s); infanticide by females seems to result in the emigration of the infant’s mother, which then allows the female immigrant to become the new breeding female of the group.