Exploring the contribution and significance of animal protein in the diet of bonobos by stable isotope ratio analysis of hair

In primates, age, sex, and social status can strongly influence access to food resources. In Pan, these criteria are assumed to influence access to vertebrate meat. However, the significance of meat in terms of its role in the nutrition of Pan is still debated. Here we present a study using stable carbon and nitrogen isotope ratios in hair samples from habituated, wild bonobos (Pan paniscus) to explore these issues. Over a period of 5 mo hair samples were collected from fresh bonobo nests at LuiKotale, Democratic Republic of Congo. Hair samples were assigned to known individuals and were of sufficient length to allow the evaluation of isotopic variation over several months. Samples of plant foods and sympatric fauna were also analyzed. The delta C-13 and delta N-15 results of the bonobo hair were remarkably homogeneous over time and for the group as a whole. There are no differences in diet between the sexes. Within the group of males, however, there was a positive correlation between dominance status and delta N-15. The isotopic data indicate that the contribution of fauna to bonobo diet is marginal and that plant food is the dietary protein source. In only some cases did elevated delta N-15 hair values correlate with observed faunivory and not correspond to the delta N-15 measured in the dominant plant foods. Given the large variation in hunting and meat eating of Pan across the African continent, the detection of seasonal changes in faunivory by elevated delta N-15 values in sectioned ape hair is a promising approach.