Immature siblings and mother-infant relationships among free-ranging rhesus monkeys on Cayo Santiago

This report examines the possible influence of the presence of immature siblings on measures of mother-infant interaction and on the timing of the mother's resumption of mating among free-ranging rhesus monkeys, Macaca mulatta, on Cayo Santiago, Puerto Rico. Data for 124 mother-infant pairs, collected between 1974 and 1986, were analysed using analysis of covariance methods. The results suggest that mothers with one or more immature daughters in addition to their infants are in contact with their infants less than those with no older immature daughters, perhaps because their infants need less protection from other group members. High-ranking mothers with older immature daughters also reject their infants significantly more than those without older daughters, and tend to begin mating earlier in the mating season than expected based on their dates of parturition the preceding birth season. In contrast, the presence of sons has relatively little impact on mother-infant interaction, or on the timing of the mother's resumption of mating.