Departures from monogamy in colonies of captive cotton-top tamarins

In a survey of institutions holding cotton-top tamarins (Saguinus oedipus), we found 23 cases of potential non-monogamy. Nine had been deliberately set up as non-monogamous units; 14 arose spontaneously. Some general trends appeared: Polyandrous groups were more likely to be stable than those with more than one potentially breeding female, and no more than one female per group successfully reared offspring at one time. Polyandry may therefore be the most viable alternative to monogamy, as recent reassessments of callitrichid mating systems have suggested.