Sustained myrmecophagy in Nigerian chimpanzees: Preferred or fallback food?

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. 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. 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. 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.

Sommer V ，Buba U ，Jesus G ，Pascual-Garrido A ... -  《-》

Chimpanzees prey on army ants at Seringbara, Nimba Mountains, Guinea: predation patterns and tool use characteristics.

Chimpanzees are renowned for their use of foraging tools in harvesting social insects and some populations use tools to prey on aggressive army ants (Dorylus spp.). Tool use in army ant predation varies across chimpanzee study sites with differences in tool length, harvesting technique, and army ant species targeted. However, surprisingly little is known about the detailed ecology of army ant predation. We studied army ant predation by chimpanzees (Pan troglodytes verus) at the Seringbara study site in the Nimba Mountains, Guinea (West Africa), over 10 years (2003-2013). We investigated chimpanzee selectivity with regards to army ant prey species. We assessed the temporal variation in army ant-feeding and examined whether army ant predation was related to rainfall or ripe fruit availability. Moreover, we examined whether chimpanzees showed selectivity regarding plant species used for tool manufacture, as well as the relationship between tool species preference and tool collection distance. Lastly, we measured tool properties and investigated the use of tool sets and composite tools in army ant predation. Seringbara chimpanzees preyed on one army ant species (D. nigricans) more often than expected based on encounter rates, which may be explained by the overlap in altitudinal distribution between chimpanzees and D. nigricans. Army ant predation was not related to rainfall or fruit availability. Chimpanzees were selective in their choice of tool materials and collected their preferred tool species (Alchornea hirtella) from greater distances than they did other species. Lastly, Seringbara chimpanzees used both tool sets and composite tools (tree perch) in army ant predation. Tool types (dig vs. dip) differed in width and strength, but not length. Tool composites were found at 40% of ant-feeding sites. Our study sheds new light on the ecology of army ant predation and provides novel insights into chimpanzee selection of army ant prey and tool species.

Koops K ，Schöning C ，McGrew WC ，Matsuzawa T ... -  《-》

Apes finding ants: Predator-prey dynamics in a chimpanzee habitat in Nigeria.

Some chimpanzee populations prey upon army ants, usually with stick tools. However, how their prey's subterranean nesting and nomadic lifestyle influence the apes' harvesting success is still poorly understood. This is particularly true for chimpanzees (Pan troglodytes ellioti) at Gashaka/Nigeria, which consume army ants (Dorylus rubellus) with much higher frequency than at other sites. We assessed various harvesting and search options theoretically available to the apes. For this, we reconstructed annual consumption patterns from feces and compared the physical characteristics of exploited ant nests with those that were not targeted. Repeated exploitation of a discovered nest is viable only in the short term, as disturbed colonies soon moved to a new site. Moreover, monitoring previously occupied nest cavities is uneconomical, as ants hardly ever re-used them. Thus, the apes have to detect new nests regularly, although colony density is relatively low (1 colony/1.3 ha). Surprisingly, visual search cues seem to be of limited importance because the probability of a nest being exploited was independent of its conspicuousness (presence of excavated soil piles, concealing leaf-litter or vegetation). However, chimpanzees preferentially targeted nests in forests or at the base of food trees, that is, where the apes spend relatively more time and/or where ant colony density is highest. Taken together, our findings suggest that, instead of employing a search strategy based on visual cues or spatial memory, chimpanzee predation on army ants contains a considerable opportunistic element.

Pascual-Garrido A ，Umaru B ，Allon O ，Sommer V ... -  《-》

Chimpanzee insectivory in the northern half of Uganda's Rift Valley: do Bulindi chimpanzees conform to a regional pattern?

McLennan MR 《-》

The nature of culture: technological variation in chimpanzee predation on army ants revisited.

Schöning C ，Humle T ，Möbius Y ，McGrew WC ... -  《journal of human evolution》