It lives in cooperative groups of 4 to 15 members with little competition within group even between breeding males. Only one female in the group will breed during breeding season with the other females suppressing the instinct. The gestation period is 140–170 days and mothers typically give birth to two offspring. Young tamarins are cared for primarily by the father and turned over to the mother only to nurse, however the entire group helps with the care of the young. Defense is a priority in a group, and when one tamarin is threatened the others will rush to its defense. The red-handed tamarin is territorial and can be aggressive, with sharp canines and claws instead of fingernails on all fingers and all but the large toe.