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Evolutionary theory predicts that individuals adapt to the living conditions faced during their lifespan. From the start of the Taï Chimpanzee Project, the foremost question was how living in a dense rainforest affects the behaviour patterns compared to the Gombe and Mahale chimpanzees, which lived in a more open environment dominated by mosaic habitat with dry woodland savanna patches and some gallery forest. Do Taï chimpanzees need a precise mental map to find their food in this dense rainforest? How does the more social nature of the social life of the Taï chimpanzees affect paternity in this population? How old is tool use, exemplified by the stone hammers used to crack nuts in Taï? Where do females come from and where are they going when they transfer between communities as young adults? Is there a difference in the cooperation level between populations when hunting arboreal monkeys and why? In all these domains, the Taï Chimpanzee Project presented new data and replicated them over different periods of time and different social groups. The role of the environment for each of this domain was discussed and proved to be essential in explaining population differences.
The chimpanzees of the Taï Forest, Côte d’Ivoire, crack highly nutritious Coula edulis nuts using anvils and hammers. While using tools to access encased food items provides obvious benefits, the energetic gain of tool-assisted foraging can be further increased by optimal selection of tools. Previous studies of animal tool selection often relied on implicit assumptions or theoretical arguments about how tool features would influence foraging efficiency, and comprehensive measures of actual efficiency are still missing. We used field observations of nut-cracking efficiency and previously published estimates of energetic costs to investigate the rate of net energy intake as a function of hammer weight and hammer material. While stones allowed for a generally more efficient performance, nut-cracking efficiency depended on an interaction of hammer weight and material. Relative performance of stones and wood varied according to the ripeness of the nuts. Chimpanzees’ tool selection tends to optimize nut-cracking in many respects. Nonetheless, we also observed a few mismatches between efficiency and selection, some of which may be explained on cognitive, motivational or cultural grounds.
First established to distinguish humans from other animals, the concept of culture provides a stimulating framework to address complexity and diversity of social responses to environmental and social factors in animals. The ‘Golden Barrier’ separating humans from other animals thinned as observations of behavioural diversity in wild chimpanzees accumulated. For 40 years, the Taï Chimpanzee Project has contributed to discussions of animal culture. The ant-dipping and nut-cracking differences reported between chimpanzee populations across Africa produced insights into cultural attributes of chimpanzees. Observed differences between neighbouring communities in the same environment of Taï forest with routine gene flow presented strong evidence for a social process sustaining group-specific cultural differences. Today, the concept of chimpanzee culture implies not only varied behaviours, group-specific forms of social learning, but also conformity within groups, accumulation of variation within traits, presence of material, symbolic and social cultural traits and diverse forms of maternal tutoring. Future work will elucidate cultural transmission mechanisms in wild animal populations.
The Taï Chimpanzee Project (TCP) was initiated in 1979 to obtain data on rainforest-living chimpanzees, as only chimpanzees in the woodland savanna of Gombe and Mahale National Park were known. Introducing ecology into the discussion on chimpanzee behavioural diversity, we identified human poaching and leopard hunting as important ecological pressures. Over 40 years, the TCP overcame two civil wars, recurrent poaching and the dramatic impact of Ebola, anthrax and respiratory diseases. The project habituated three neighbouring chimpanzee communities, integrating many local students and assistants to ensure continuity of data collection and the security of chimpanzees, even in times of extreme political instability. Taï National Park has become an island within a huge cocoa and coffee plantation, which the chimpanzees and the TCP survived thanks to the extreme dedication of local and international project members, a project-specific law enforcement programme, a complete health monitoring programme, and the support of local human populations. Taï chimpanzees have become famous for their nut-cracking behaviour, high level of cooperative hunting and extensive cultural diversity.
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