Nonmaternal Infant Handling in Wild White-Headed Langurs (Trachypithecus leucocephalus)

Infants of many primate species have extensive interactions with group members other than their mothers, which can affect an infant’s fitness. Patterns of nonmaternal infant handling vary according to the mother’s response as well as the number, sex, age, and dominance ranks of social partners. The primary goal of this study was to identify the basic pattern and explore the function of nonmaternal infant handling behavior in wild white-headed langurs (Trachypithecus leucocephalus) at the Nongguan Hills in Guangxi, Southwest China. We report nonmaternal interactions in the first 3 mo after birth for 15 infants born during six birth seasons in a 67-mo field study. The nonmaternal infant handling we observed was generally in the form of caregiving, and mothers permitted most handling attempts. Infants were handled by nonmothers from the first day after birth. Infants spent 20–30% of the daytime associated with nonmothers during the first month of life, and time in contact with nonmothers decreased with infant age. Rates of nonmaternal infant handling varied significantly with the sex and age of handlers. Juvenile and subadult females handled infants significantly more than expected from their proportional representations in the group, whereas adult females did so less frequently than expected. Older male infants and juvenile males rarely handled infants, and adult males never did so. Infant handling behavior showed no correlation with the dominance rank of handlers relative to the mothers. Our data, although limited in some analyses, are in line with the predictions of the learning-to-mother hypothesis, but do not support the female competition or alliance formation hypotheses.