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Abstract

Abstract Comparative studies on tool technologies in extant primates, especially in our closest living relatives, offer a window into the evolutionary foundations of tool use in hominins. Whereas chimpanzee tool technology is well studied across populations, the scarcity of described tool technology in wild populations of our other closest living relative, the bonobo, is a mystery. Here we provide a first report of the tool use repertoire of the Kokolopori bonobos and describe in detail the use of leaf-umbrellas during rainfall, with the aim to improve our knowledge of bonobo tool use capacity in the wild. The tool use repertoire of the Kokolopori bonobos was most similar to that of the nearby population of Wamba and comprised eight behaviors, none in a foraging context. Further, over a 6-month period we documented 44 instances of leaf-umbrella use by 22 individuals from three communities, suggesting that this behavior is habitual. Most leaf-umbrella tool users were adult females, and we observed a nonadult using a leaf-umbrella on only a single occasion. While the study and theory of tool technologies is often based on the use of tools in foraging tasks, tool use in bonobos typically occurs in nonforaging contexts across populations. Therefore, incorporating both foraging and nonforaging contexts into our theoretical framework is essential if we wish to advance our understanding of the evolutionary trajectories of tool technology in humans.