Infant care, nutritional development and lactation in chimpanzees at Ngogo, Kibale National Park, Uganda
Understanding the factors affecting the time from complete dependence on maternal milk to nutritional independence (i.e. infant nutritional development), and obtaining accurate data on the timing of infant feeding transitions are needed to ultimately understand species-specific life history components. I quantitatively documented infant nutritional development, assessed the patterning of maternal investment through lactation over the course of infancy, and investigated the effects of alloparenting on the speed with which infants were weaned, in approximately 50 infant chimpanzees (Pan troglodytes schweinfurthii) and their mothers of one wild community at Ngogo, Uganda. Measuring nutritional development in wild primates is difficult through observations alone because confirming dietary intake of infants is challenging. I therefore used behavioural data in combination with novel physiological measures of fecal stable isotopes (Î´13C:Î´15N, %N) to assess age-specific infant nursing and foraging, determine the relative contributions of maternal milk and other foods in infant diets, and assess the timing and process of weaning. First, I showed that fecal stable isotopes can be successfully used to track infant nutritional development, and found that the weaning process begins and ends by around 1 and 4 years of age, respectively, but that offspring could continue to comfort nurse for years afterwards. Second, I found that chimpanzees showed a multi-year and plateauing lactation pattern. Like humans, chimpanzee mothers provided a steady supply of milk while infants increasingly supplemented their growing energy needs with solid foods until the contribution of milk relative to other food in the diet was sufficiently low that milk no longer constituted a dietary need for offspring. Third, infants who were held and carried more by alloparents showed accelerated weaning rates, and their mothers experienced a reduced lactation effort, suggesting that alloparenting in chimpanzees may have a positive effect on female reproductive rates. This dissertation contributes to models of chimpanzee infant care, nutritional development, and patterning of lactation required to understand the evolution of life history patterns in hominins, including relatively earlier weaning and increased female reproductive rates.
Chimpanzee, Infant care, Lactation, Primate, Stable isotopes, Weaning
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