COMPETITION TO CARRY INFANTS IN CAPTIVE FAMILIES OF COTTON-TOP TAMARINS (SAGUINUS-OEDIPUS)

The Callitrichidae (marmosets and tamarins) typically produce twins, and have communal rearing systems in which all group members help care for the infants. It has been hypothesised that helpers benefit in some way from assisting in infant care. If so, then competition to carry infants would be predicted. This was tested in a study of 14 litters of captive cotton-top tamarins (Saguinus oedipus). All occurrences of infant transfers (movements of infants from one caretaker to another) were recorded from birth to 12 weeks. Individuals in larger groups were less likely to reject infants, more likely to actively take infants, more likely to resist attempts by others to take, and more likely to intervene in transfers, suggesting increased competition to carry in large groups. Singletons were rejected less than twin infants, again suggesting the existence of competition amongst caretakers. Mothers rejected infants more frequently than fathers; young tamarins rejected infants more than older tamarins. There was evidence that carrying by juvenile siblings and by adult daughters was limited by other group members. There was evidence that adult sons and sub-adult sons and daughters competed most strongly, and were more likely to attempt to limit carrying by other group members. These results were interpreted in the light of hypotheses suggesting that the benefits to be gained from helping may differ amongst age-sex classes.