The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)

Fecal stable isotopes (δ13C:δ15N, %N) used to track infant nutritional development and reveal average weaning age in wild chimpanzees


1Department of Anthropology, University of Toronto, 2Department of Anthropology and Archaeology, University of Calgary, 3Department of Anthropology, Yale University

April 16, 2016 3:00, A 703/704 Add to calendar

The lengths of time between complete and partial dependence on maternal milk and independent feeding are key biomarkers of infant nutritional development and include life history parameters used to distinguish evolutionary changes. Identifying the timing and duration of nutritional development in nonhuman primates is difficult from observations; infants may appear weaned during the day but may continue to nurse at night, or weaned individuals can be classified inaccurately as nursing infants when they make nipple contact for comfort only. To assess observational limitations, we used fecal stable isotopes (δ13C:δ15N, %N) to physiologically track the diets of infant chimpanzees at Ngogo, Uganda, as they transitioned from reliance on maternal milk to adult foods. We analyzed 614 fecal samples from 48 infants varying in age from two months to one year after birth of a sibling, each matched to samples collected from their mothers on the same day. Due to trophic level effects, infants ≤1 year old had average δ15N, δ13C and %N that were 2.0‰, 0.8‰ and 1.3% greater than their mothers, respectively. These differences decreased gradually with increasing infant age. Isotopic evidence revealed that infants were weaned by 4 years old – more than a year earlier than nipple contacts ceased, which suggests comfort nursing occurred. Juvenile siblings had 0.3% greater %N than mothers, and 0.1‰ greater δ15N, which indicates no nursing overlap between siblings. Our results contribute to a model of chimpanzee nutritional development that is required to ultimately understand human infant feeding, development, and early life history patterns.

Thank you to the L. S. B. Leakey Foundation and The Explorers Club for generously funding this research.