Isotopic assessment of marine food consumption by natural-foraging chacma baboons on the Cape Peninsula, South Africa

ObjectivesStable isotope analysis has been used to investigate consumption of marine resources in a variety of terrestrial mammals, including humans, but not yet in extant nonhuman primates. We sought to test the efficacy of stable isotope analysis as a tool for such studies by comparing isotope- and observation-based estimates of marine food consumption by a troop of noncommensal, free-ranging chacma baboons. Materials and methodsWe determined C-13 and N-15 values of baboon hair (n=9) and fecal samples (n=144), and principal food items (n=362). These values were used as input for diet models, the outputs of which were compared to observation-based estimates of marine food consumption. ResultsFecal C-13 values ranged from -29.3 to -25.6 parts per thousand. N-15 values ranged from 0.9 parts per thousand to 6.3 parts per thousand and were positively correlated with a measure of marine foraging during the dietary integration period. Mean (+/- SD) C-13 values of adult male and female baboon hairs were -21.6 parts per thousand (+/- 0.1) and -21.8 parts per thousand (+/- 0.3) respectively, and corresponding N-15 values were 5.0 parts per thousand (+/- 0.3) and 3.9 parts per thousand (+/- 0.2). Models indicated that marine contributions were 10% of baboon diet within any season, and contributed 17% of dietary protein through the year. DiscussionModel output and observational data were in agreement, both indicating that despite their abundance in the intertidal region, marine foods comprised only a small proportion of baboon diet. This suggests that stable isotope analysis is a viable tool for investigating marine food consumption by natural-foraging primates in temperate regions.