Abstract

Cultural variation has been identified in a growing number of animal species ranging from primates to cetaceans. The principal method used to establish the presence of culture in wild populations is the method of exclusion. This method is problematic, since it cannot rule out the influence of genetics and ecology in geographically distant populations. A new approach to the study of culture compares neighbouring groups belonging to the same population. We applied this new approach by comparing ant-dipping tool length between two neighbouring communities of chimpanzees (Pan troglodytes schweinfurthii) in the Kalinzu Forest, Uganda. Ant-dipping tool length varies across chimpanzee study sites in relation to army ant species (Dorylus spp.) and dipping location (nest vs. trail). We compared the availability of army ant species and dipping tool length between the two communities. M-group tools were significantly longer than S-group tools, despite identical army ant target species availabilities. Moreover, tool length in S-group was shorter than at all other sites where chimpanzees prey on epigaeic ants at nests. Considering the lack of ecological differences between the two communities, the tool length difference appears to be cultural. Our findings highlight how cultural knowledge can generate small-scale cultural diversification in neighbouring chimpanzee communities.

Highlights

  • Recent studies have examined in detail the variation between neighbouring chimpanzee communities in the Taï Forest, Ivory Coast[9,10,11]

  • We examined the relationship between the availability of the different army ant species and their consumption by M-group chimpanzees

  • Ant-dipping tool length differed between the two neighbouring chimpanzee communities at Kalinzu, despite them having identical army ant availabilities

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Summary

Introduction

Recent studies have examined in detail the variation between neighbouring chimpanzee communities in the Taï Forest, Ivory Coast[9,10,11]. Community differences in a foraging context were found in the selection of hammers for nut-cracking[9,10], as well as in termite prey selection and in strategies of army ant nest raiding[11]. Longer tools are used for more aggressive army ant species (‘epigaeic’), and shorter tools for less aggressive species (‘intermediate’) This pattern was found both within community[15] and across populations[17]. We investigated differences in ant-dipping tool length between two neighbouring communities of chimpanzees (Pan troglodytes schweinfurthii) in the Kalinzu Forest, Uganda. If we find differences in tool length between neighbouring communities without finding differences in army ant species availability, these differences are highly likely to have a cultural basis. We analysed the relationship between army ant species targeted and dipping tool length

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