Iulia Badescu is a PhD candidate at the University of Toronto. She was awarded a Leakey Foundation research grant during our 2015 spring cycle for her project entitled “Investigating the infant nutritional development of wild chimpanzees.”
I am investigating the infant nutritional development of chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda. Infant nutritional development is the time from complete dependence on maternal milk to nutritional independence, and includes three stages: exclusive suckling, transitional feeding (from first solid food consumption to suckling cessation) and weaning. Little is known about chimpanzee infant diets and mother-infant interactions. A model of infant nutritional development in wild chimpanzees is required to better understand the evolution of human infant feeding and care, and my project will acquire the primary data needed to achieve this task. Identifying the key differences and similarities between the nutritional development of chimpanzees, humans and other primates will help us delineate the evolutionary forces responsible for the variable patterns of infant feeding shown across primates and within contemporary human populations.
I am using a combination of behavioral and fecal stable isotope data to track the progression of infants’ diets from 100% maternal milk to 100% adult foods. My aim is to quantitatively document each stage of infant nutritional development, and the development of ecological competence in wild chimpanzees. Over 11 months at Ngogo, I watched infants nurse, forage, learn to eat solid foods, and interact socially with their mothers and others. With the help of two field assistants, I collected almost 1000 fecal samples from infants and their mothers. I am currently working in the Archeological Chemistry Lab and Isotope Sciences Lab at the University of Calgary to determine the stable isotope compositions (δ15N, δ13C, %N) of the fecal samples collected.
The stable isotopes of various foods are reflected in the tissues and feces of consumers. Chimpanzee infants consuming mostly maternal milk show different fecal stable isotope profiles than their mothers, who eat a plant-based diet. As infants progress through transitional feeding and weaning, their isotope profiles gradually resemble those of their mothers until they are identical, when weaning is complete. It is useful to compare isotopic assessments of infant diets with observations of nursing and feeding because behavioral data alone may not allow primatologists to reliably document nutritional development. An infant may appear weaned from daytime observations but may continue to nurse at night, when observations are not conducted. Alternatively, a weaned individual that continues to contact the mother’s nipple for comfort rather than nutrition may be classified inaccurately as a nursing infant from observations. To remedy these observational limitations, I will compare my behavioral data of nursing and infant feeding with stable isotopes (δ13C, δ15N, %N) of fecal samples collected during the same time period. This comparison will identify any discordances between the behavioral and isotopic assessments of infants’ diets, and allow me to reliably determine the timing and duration of infant nutritional development in wild chimpanzees.
I am grateful to the Leakey Foundation for funding the stable isotope laboratory analyses. This research is only possible with the support of my supervisor, Dr. Daniel Sellen (University of Toronto) and our collaborators, Drs. Anne Katzenberg (University of Calgary), David Watts (Yale University), Kevin Langergraber (Arizona State University), and John Mitani (University of Michigan).