Identifying Species in Chimpanzee (Pan troglodytes) Feces: A Methodological Lost Cause?

Ascertaining the full range of dietary constituents of a primate population allows the identification of habitats with important food resources and can assist efforts to conserve primates. For unhabituated populations, we can acquire otherwise unobtainable dietary information from macroscopic inspection of fecal samples. This method has made a significant contribution to understanding food intake in various primate species. Increasing knowledge of the omnivorous diet of our closest living relatives, the common chimpanzee (Pan troglodytes) and the bonobo (P. paniscus), which range and forage in various habitats to meet daily nutrient requirements, provides more scope to assess human omnivory and its evolution from our last common ancestor. However, macroscopic inspection may lead to bias toward undigested and therefore identifiable food items, e.g., fruit seeds, vs. pulverized components, e.g., leaves, that are unidentifiable at this level. This study seeks to validate findings from macroscopic inspection by comparing species identified in fecal samples from select individuals vs. data from direct observations of their feeding. We collected data from 10 adult chimpanzees of the Kanyawara community in Kibale National Park. We identified 86% of species from which fruit had been eaten vs. only 21% from which leaves had been eaten in fecal samples analyzed. This study provides empirical support for previous assumptions and confirms the limitations of macroscopic inspection of feces for identifying the nonfrugivorous dietary elements to species level. However, valuable insights into seasonality of diet can be gleaned from macroscopic inspection. Also, if we combine data on species identified in feces with direct observation of food intake, we can establish when food items were eaten, which enables estimations of gut passage rates for wild populations. Finally, analyzing fecal samples collected from various group members can provide insight into the dietary repertoire at the individual level.