Tamarins and chimpanzees differ in many aspects of their behavior, biology, and evolutionary history; however, both primates are heavily dependent on a diet of ripe fruits during all months of the year (reviewed in Digby et al. 2011; Stumpf 2011). In addition, previous research on cognition in tamarins and chimpanzees indicates that individuals retain spatial information concerning the location of many feeding sites (e.g., Garber 2000; Janmaat et al. 2013a; Normand et al. 2009). Since primates show a high level of site fidelity (Janmaat et al. 2009) and commonly rely on sessile food sources that are revisited many times over a limited part of the year (such as termite nests and trees producing fruits, leaves, flowers, and/or exudates), one might expect foragers to reuse a limited set of travel routes, return to previously visited feeding sites, and search for new food patches in locations nearby current feeding sites.

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.

A central component of primates’ social ontogeny is play with conspecifics. Play is constrained by ecological factors, especially food abundance, and social play is most likely limited by partner availability, which in turn can be related to ecology. However, how much social and ecological factors collectively influence social play rates has not yet been investigated. We used a multivariate approach to test to what degree fruit and partner availability affected social play rates of wild immature chimpanzees in Taï National Park. As fruit abundance and partner availability increased, infant and juvenile play rates rose, with juvenile play being affected more by fruit abundance than infant play. Partner availability predicted infant play rates better during the low than the high fruit availability season, which was not the case for juvenile play. Our results indicate that young chimpanzees face a trade-off in allocating time or energy to foraging and social play, with foraging becoming increasingly dominant with age. This joint analysis of social and ecological factors suggests that food abundance modulates the effect of partner availability on social play rates in young chimpanzees.

Meat sharing is common in chimpanzees. While being well-studied, it is still unclear what drives meat owners to relinquish nutritional benefits in favour of group members. The topic is rich in theoretical models, with support for different hypotheses coming from various chimpanzee populations. Few studies have considered several alternative hypotheses simultaneously, which provides insight into how multiple mechanisms interact to enable meat sharing. We investigated whether Reciprocal Altruism, Sharing-under-pressure, Mutualism, or Costly Signalling can explain meat sharing in Taï chimpanzees. We found evidence that chimpanzees exchange meat for support in aggressive interactions, supporting Reciprocal Altruism. We found partial support for Mutualism, as individuals who caught the prey ate more than others, and hunters who begged were more likely to receive meat than others. Finally, we found that begging led to sharing, possibly supporting the Sharing-under-pressure hypothesis. Various mechanisms can lead to meat sharing; the prevalence of one mechanism over another might result from their ability to adapt to the specific environmental and social conditions of the population.

It has become increasingly apparent that different chimpanzee populations behave differently. Most behaviours and vocalizations are observed across all or most populations. Some behaviours, however, are specific to few populations and different populations behave disparately when solving the same problems. Instead of speaking about the ‘typical’ behaviours, one can probably speak better of a range of chimpanzee behaviours. Between populations, behaviours can range widely. For good comparability and to avoid biases, observers either need to unilaterally use the same protocol or it needs to be apparent how and which data have been collected. Here, we clarify the protocol under which long-term data are collected by the Taï Chimpanzee Project. Despite regular changes to improve and update long-term data collection, our core data collection has remained unchanged, allowing use of the whole data set in analyses. With this chapter, not only can we interpret results generated from the Taï database with more accuracy, but also provide more accessibility for comparisons than currently available. One of the outcomes of this chapter will be making comparisons across study populations easier.

Demography and life-history data provide key information for our interpretation of the evolution and ecology of a species. Gathering reliable data can be a challenge, especially in species with long life spans such as the great apes. Only long-term field projects can compile trustworthy demography data, allowing us to access life-history measures. Here, we present the demography of four communities of wild chimpanzees (North, South, Middle and East Groups) located in Taï National Park, Côte d’Ivoire, following observations of individual chimpanzees for almost 40 years. We will provide demography data on birth, mortality, community size, age and sex ratios, among others, and translate these into life-history measures related to reproductive strategies (age of mother at birth of first infant, interbirth interval, etc.) and fitness (reproductive success, longevity, etc.). A comparison with available data from other long-term chimpanzee study sites will be made and we will discuss the life-history adaptations of Taï chimpanzees to the challenges they are facing.

Social network analysis is a widely applied tool to study the social organization of different species. Only few studies have investigated social network changes over time. A previous study of the North Group chimpanzees in Taï National Park indicated network structure changes with decreasing community size. We investigated how two natural ‘knockouts’, i.e. sudden large-scale declines in community size, affected association networks. Network dynamics following the 1992 knockout, during which eight individuals died, showed a delayed response: in the first months, association rates were lower than expected, and only after seven months did they converge to expected community-size–specific level. In contrast, network dynamics following the 1994 knockout, during which 12 individuals died, showed no deviation from expected community-size–specific levels. Thus, chimpanzee association networks can react differently to large-scale declines in community size. Differences might be related to the identity of deceased individuals and knockout amplitude. The patterns of observed changes did not support the idea that large-scale knockouts lead to strong disturbances of chimpanzee communities.

Across Africa, chimpanzee communities exhibit large behavioural diversity not exclusively explained by ecological or genetic variation. However, excluding subtle environmental factors is difficult when comparing far-apart populations. Taï National Park offers a unique opportunity to explore the impact of social learning on behavioural diversity. The Taï South and Djouroutou communities live only 60 km apart in a continuous ecosystem. However, these groups apply semi-different techniques when nut-cracking. Djouroutou chimpanzees crack five species of nuts, exclusively using stone tools. Taï South only cracks four of those species, using stone and wooden tools, and does not exploit abundant Sacoglottis gabonensis nuts. Moreover, this group uses stone and wooden tools. Here, we compared tool material availability and tool choice. Our results showed that both groups did not differ in available nut trees and access to different materials. The communities responded to these ecological conditions differently than predicted if availability was the only factor responsible for shaping behaviour. This highlights the potential role of cultural behaviour in wild chimpanzee feeding ecology.

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.