Tool use by Nigeria-Cameroon chimpanzees for driver ant predation in Kom-Wum Forest Reserve, North-West Region Cameroon

Abstract

Chimpanzees feed on driver ants (Dorylus sp.) using different tools and predation techniques that vary among populations and can be affected by availability of ant species as well as ecological and social-learning factors. At the Kom-Wum Forest Reserve (KWFR) in Cameroon, we investigated tool use behavior in Nigerian-Cameroon chimpanzees (Pan troglodytes ellioti), examining the characteristics of tools used in driver ant predation, looking for possible seasonal patterns and comparing our results to those from other study sites. We recovered 83 tools along line transects and recces (reconnaissance) during two seasons. We found that chimpanzees used tools with blunting and dirty ends (possible digging and probing tools) and tools without (dipping tools), in driver ant predation. Tools with dirty ends tended to be thicker (N = 52), and thinner tools were less likely to have dirt (N = 31). Tools recovered in the wet season (N = 62), were significantly shorter and thicker than those recovered in the dry season (N = 21). Furthermore, driver ant tools recovered at KWFR are on average the longest yet recorded insect dipping tools for chimpanzees comparable to those used in North Uele. We found no evidence of nut-cracking, tool use for honey bee nor termite consumption and did not observe the potential prey remains in chimpanzee faeces despite their presence in the reserve. Our results suggest that seasonality significantly contributes to a divergence in the form of tools selected for driver ant predation.