They roam in very large groups of 20 to 100, some time up to 300 individuals. They all sleep together at night, and then divide up to go and look for food, using complex vocalisation systems which have up to 20 distinct calls.
It is common to see these squirrel monkeys in mixed groups, moving along with other primate species and birds. Remarkably, the brain mass to body mass ratio for squirrel monkeys,2 gives them the largest brain, proportionately, of all the primates. Females give birth to one young per year and males play no part in rearing the young, although other females will help carry and watch over infants.