Chimpanzee tool technology in the Goualougo Triangle, Republic of Congo

With the exception of humans, chimpanzees show the most diverse and complex tool-using repertoires of all extant species. Specific tool repertoires differ between wild chimpanzee populations, but no apparent genetic or environmental factors have emerged as definitive forces shaping variation between populations. However, identification of such patterns has likely been hindered by a lack of information from chimpanzee taxa residing in central Africa. We report our observations of the technological system of chimpanzees in the Goualougo Triangle, located in the Republic of Congo, which is the first study to compile a complete tool repertoire from the Lower Guinean subspecies of chimpanzee (Pan troglodytes troglodytes). Between 1999 and 2006, we documented the tool use of chimpanzees by direct observations, remote video monitoring, and collections of tool assemblages. We observed 22 different types of tool behavior, almost half of which were habitual (shown repeatedly by several individuals) or customary (shown by most members of at least one age-sex class). Several behaviors considered universals among chimpanzees were confirmed in this population, but we also report the first observations of known individuals using tools to perforate termite nests, puncture termite nests, pound for honey, and use leafy twigs for rain cover. Tool behavior in this chimpanzee population ranged from simple tasks to hierarchical sequences. We report three different tool sets and a high degree of tool-material selectivity for particular tasks, which are otherwise rare in wild chimpanzees. Chimpanzees in the Goualougo Triangle are shown to have one of the largest and most complex tool repertoires reported in wild chimpanzee populations. We highlight new insights from this chimpanzee population to our understanding of ape technological systems and evolutionary models of tool-using behavior.