Biology

© Liran Samuni / TCP

Western chimpanzees live in multimale-multifemale, fission-fusion communities (meaning that the social unit is not cohesive and may split and merge depending on time of day, availability of reproductive females and food). Communities typically range in size from 11 to 63 individuals. Chimpanzees are generally male philopatric, meaning that females tend to leave their natal community when they reach reproductive age. They are a long-lived species (maximum lifespan c.50 years) with extensive maternal care; infant dependency is among the longest in the animal kingdom. Chimpanzees build nests to sleep in every night and occasionally to rest in during the day. Nests are valuable indirect signs of chimpanzee presence and are counted in most great ape surveys.

Most chimpanzee communities demonstrate some degree of territorial defence (Herbinger et al. 2001; Samuni et al. 2017). However, when the frequency of inter-community encounters increases because chimpanzees are forced to shift their home range due to habitat loss or disturbance, there is a risk that such interactions can escalate into physical fights that can be fatal. Each community occupies a home range, varying from 8 km2 to 89 km2, depending on resource availability. Particularly in the hot and dry northern reaches of the range, chimpanzees are dependent upon the availability of freestanding water sources. Western chimpanzees live in a wide range of ecotypes, from the sparse and arid habitats of Senegal and Mali to the wet lowland rainforests of Liberia and southern Côte d’Ivoire, as well as agricultural and anthropogenic landscapes across the region in question, notably in Sierra Leone, Guinea and Guinea Bissau. These habitats vary considerably in their forest cover, from 2% or less in the northernmost savanna mosaics (Garriga et al. 2019; Lindshield et al. 2019; Wessling et al. 2020) to high degrees of canopy cover in forested areas (see, for example, Taï National Park).

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© Liberia Chimpanzee Rescue & Protection

Chimpanzee diets consist of plant matter, with a strong preference for fruit, although all communities studied also eat meat (often other primates, such as galagos Galago spp. or colobus monkeys Colobus and Piliocolobus spp.), insects (termites, ants) and insect products (honey, insect nests). In some locations, chimpanzees are known to crack and eat nuts (Bossou; Sapo; Taï National Park), fish for algae (Humle et al. 2011; Boesch et al. 2017a), and hunt primates with the help of tools.

Western chimpanzees show considerable behavioural flexibility, which enables them to cope with and persist in human-impacted habitats. This includes dietary flexibility with human crop consumption, the use of leaf tools to ingest palm wine, and anthropogenic landmarks (such as roads) and other human intrusions (such as snares).