The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

The meaning of weaning in wild Phayre’s leaf monkeys (Trachypithecus phayrei crepusculus)


1Department of Anthropology, Stony Brook University, 2Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 3Department of Anthropology, University of Illinois, Urbana-Champaign

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In primates, weaning is often considered to be a long lasting process characterized by a very gradual shift toward energetic independence from the mother. Although there is agreement about the importance of the age at nutritional independence, it remains difficult to determine. Some emphasize the moment when mothers resumed cycling as the best measure while others use the cessation of nipple contact which often occurs much later. A recent study on captive Francois’ langurs supports the latter by confirming nursing effects via stable isotope ratios in the feces of an infant assumed to be close to independence. Here we investigate these two measures of weaning age in 51 wild Phayre’s leaf monkey infants at Phu Khieo Wildlife Sanctuary (Thailand). Infants averaged 15.5 months (range 8-25) when their mothers’ resumed mating and 18.9 months (range 12-28) at last nipple contact. If nipple contact lasted less than 16 months, infants did not survive to three years, emphasizing that the end of the nursing period might still be energetically important. For most infants nursing stopped only after their mother had re-conceived, usually during her last trimester. We found little support for the importance of weaning food in the timing of independence because, relative to the annual peak in food availability, the resumption of mating occurred too early and the cessation of nipple contact too late. Instead, there appears to be a compromise between maternal investment in the subsequent infant and a maximum length of investment in the current infant via nipple contact.

Data collection supported by National Science Foundation: BCS-0215542, BCS-0452635, BCS-0542035, BCS-0647837; Wenner-Gren Foundation: 7241, 7639; Leakey Foundation; and American Society of Primatologists.

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