Objective: At some sites across Africa, chimpanzees consume army ants, often aided by stick-tools, although consumption frequencies vary greatly. Other populations do not eat these insects at all, despite apparent abundance. The relative importance of myrmecophagy 2 for chimpanzee diet therefore remains unclear. Major functional hypotheses consider army ants either as a preferred food or a fallback fare when preferred foods are scarce. We test these hypotheses for chimpanzees at Gashaka / Nigeria, where chimpanzees consume army ants much more frequently than elsewhere.Methods: Long-term records on seasonality of climate and availability of fruit as the chimpanzees' preferred staple food are compared to rates of recovered army ant dipping wands and army ant remains in faeces.Results: Despite strict seasonality in terms of rainfall and fruit abundance, myrmecophagy does not negatively correlate with fruit availability. Instead, ant eating is sustained year round at high levels, with 44% of faeces containing remains.
Conclusions:Results contradict the fallback hypothesis and support the hypothesis of ants as preferred food. Nevertheless, ant-meals can normally provide only negligible amounts of nutrients. At Gashaka, however, nutritional yield may be significant, given that an ant dipping session provides 13 mg of dry weight to a chimpanzee. The species exclusively eaten here, Dorylus rubellus, might be particularly aggressive, thus resulting in greater harvesting success than elsewhere. Army ants may thus serve as a diet supplement or complement in terms of macro or micronutrients. We also speculate that dietary choices likely contain social dimensions that may strengthen group identity.