Sustained myrmecophagy in Nigerian chimpanzees: Preferred or fallback food?

OBJECTIVE

At some sites across Africa, chimpanzees consume army ants, often aided by plant tools, although consumption frequencies vary greatly. Other populations do not eat these insects at all, despite apparent abundance. The relative importance of this type of myrmecophagy for chimpanzee diet therefore remains unclear. We investigate if army ants constitute a preferred food or a fallback resource for chimpanzees at Gashaka, Nigeria, where army ants are consumed much more frequently than elsewhere.

METHODS

Long-term records on temporal variation of climate and availability of fruit as the chimpanzees' preferred food are compared with rates of recovered army ant dipping wands and army ant remains in feces.

RESULTS

Despite strict seasonality of rainfall and fruit abundance, myrmecophagy does not negatively correlate with fruit availability. Instead, army ant eating is sustained year round at high levels, with 44% of feces containing remains.

CONCLUSIONS

Results contradict the fallback hypothesis and support the hypothesis that ants are a preferred food. Nevertheless, compared with fruit, ant-meals can normally provide only negligible amounts of nutrients. At Gashaka, however, nutritional yield may be significant, given that ant-dipping sessions provide on average 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 hence serve as a diet supplement or complement in terms of macro- or micronutrients.