Embraces for infant handling in spider monkeys: evidence for a biological market?

The presence of young infants influences female primate social behaviour, in particular social grooming, which may be exchanged for infant access within a biological market place ( Henzi & Barrett, 2002, Animal Behaviour, 63, 915e921). Although social grooming is common among Old World primate species, it is rarely observed in a number of NewWorld primate species, including spider monkeys. We investigated whether affiliative behaviour is exchanged for infant handling among wild female spider monkeys, Ateles geoffroyi yucatanesis. Occurrences of approaches, grooming and embraces received by 15 adult females were compared when they had infants less than 6 months old (` mothers') and at all other times. The occurrence of grooming was not influenced by the presence of infants. However, females received significantly more approaches and embraces when they were mothers compared to all other times. As mothers, they received significantly more embraces than they gave indicating that the increase in friendly behaviour received was due to increased interest from other females and not simply a general increase in sociality. The exchange of embraces for infant handling was subject to a market effect as the proportion of embraces given to mothers followed by infant handling decreased when fewer infants were present in the group. Although spider monkeys use embraces as the primary means of gaining access to infants, whether embraces provide long- term benefits to the recipient, remains to be determined. Thus, embraces may only serve to signal benign intent and reassure mothers during tense interactions such as infant handling. Crown Copyright (C) 2007 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. All rights reserved.