The nutritional quality of male chimpanzee diets in a semiarid savanna

Nutritional ecology is vital to understanding food selection in chimpanzees (Pan troglodytes). However, there are knowledge gaps for chimpanzees in savanna landscapes concerning the nutrients of their foods as well as their daily energy and macronutrient intakes. The aims of this study are to (1) examine how adult male chimpanzees in a semiarid savanna select their foods and (2) compare chimpanzee foods between the savanna and forest. We conducted full-day focal follows to observe food processing behavior (87 days) and comprehensively measure daily food intake (25 days). We sampled 49 plant and four insect species to estimate their energy and macronutrient contents. Food consumption correlated positively with its profitability (caloric yield per hour) but was not associated with food abundance or distribution. Daily intakes of metabolizable energy and of water-soluble sugars were higher in the baobab (Adansonia digitata) season than in the non-baobab season and social rank boosted sugar intakes, suggesting that high-sugar foods are prized by Fongoli chimpanzees. In support of the idea that a scarcity of ripe fleshy fruits is an environmental pressure at Fongoli, chimpanzees commonly ingested unripe fruit and seeds, mostly of nonfleshy types, potentially for their protein content or as moderate sources of sugar, fat, and water. Our study indicates that the savanna is not a low-protein habitat and suggests ways that chimpanzees—and potentially early hominins—have adapted to meet daily nutritional requirements in a savanna environment.