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Chimps in Sierra Leone adapt to human-impacted habitats, but threats remain

Camera trap photo of a chimpanzee with mangoes.

Camera trap photo of a chimpanzee with mangoes. Photo: Tacugama Chimpanzee Sanctuary/DICE, University of Kent

  • Western chimpanzees are adapting to survive in severely degraded habitat, a new study says.
  • However, the study also finds the abundance of western chimpanzees in Sierra Leone is impacted by even secondary roads.
  • Ensuring the long-term survival of western chimps calls for changes in agriculture, roads and other development, researchers say.

A new study of western chimpanzees in southwestern Sierra Leone finds they are adapting to survive in severely degraded habitat. But researchers say this doesn’t obviate the need to minimize the impacts of development such as roads and promote less-damaging approaches to farming by local people.

Despite the gradual loss of most of their original habitat, the chimpanzees in Moyamba district have survived thanks to a particular set of conditions, according Tatyana Humle, a senior lecturer in conservation and primate behavior at the University of Kent, U.K., and one of the authors of the study.

“In this case, the main driver of forest loss in the locality is slash and burn agriculture which has taken place over generations, and some key natural resources remain in the landscape,” Humle told Mongabay. “The study area is dominated by semi-domesticated oil palm: the oil palm is native to West Africa, and people tend not to cut them down as they are also useful to people for the fruit, palm leaves for construction materials, and local wine production.”

Oil palm (Elaeis guineensis) is a key species for the chimpanzees, which typically build a new nest every night: in the study area, all the nests were built in oil palms in the absence of other mature nesting tree species. Another tree species usually spared by farmers because they eat the fruit is the Guinea plum (Parinari excelsa); the plums are also a preferred food item for chimpanzees.

The relatively small human settlements in the area and local tolerance for the chimps’ presence are also key factors. “[People] do not persecute or kill the chimps out of fear or because they forage on their crops — which chimpanzees do in this study area, probably because wild food resources are limited,” Humle said.

Moyamba residents standing in front of mud-brick and thatched roof homes.
People in Moyamba District live in relatively small settlements; the original forest has largely been replaced with farmland and stands of semi-wild oil palm. Photo: Red Cross CC by ND 2.0

Chimps in the anthropocene

The western chimpanzee (Pan troglodytes verus) is today found in eight West African countries, with the greatest numbers found in Guinea, Liberia and Sierra Leone. The subspecies vanished from parts of its historic range in Benin, Burkina Faso and Togo during the 20th century. Today, it is all but extinct in Ghana, and populations in Côte d’Ivoire have also declined sharply in recent decades.

Sierra Leone is home to perhaps 10 percent of the 53,000 western chimpanzees still in the wild; more than two-thirds of that number live outside of the country’s protected areas.

Western chimps are found in a variety of habitats, including savanna grasslands and dense rainforest. But habitat loss across their range due to expansion of human populations and agriculture, mining and development of infrastructure, is the principal threat to the survival of the subspecies. Combined with diseases such as Ebola and the hunting of the apes for bushmeat and traditional medicine — or in retaliation for the animals’ raids on crops — destruction or degradation of habitat has seen western chimp numbers crash, placing them on the IUCN’s Red List of critically endangered species.

Researchers from the Autonomous University of Barcelona, Spain’s Institute of Game and Wildlife Research, the University of Kent, and Sierra Leone’s Tacugama Chimp Sanctuary set out to investigate how anthropogenic factors (roads, settlements, abandoned settlements and human presence) and available habitat (swamps, farmlands and mangroves) affected the abundance of chimpanzees in Moyamba.

In this part of the country, the original forest has largely been replaced with active and abandoned farmland and stands of semi-wild oil palms; the district is lightly veined with unpaved roads and some relatively undisturbed areas of swamps and mangroves remain. It is a common pattern across West Africa’s forest zones, where a mosaic of farmland, fallow land and remnant forest has become the dominant landscape as human population growth, industrial agriculture and urban expansion encroach on natural habitat.

The team set up 24 infrared camera traps in farmlands, swamps and mangroves across the district during an eight-month period between 2015 and 2016, and captured about 75,000 images.

As expected, the camera trap data showed Moyamba’s chimps preferred to stay close to swamps and tended to avoid roads. But contrary to expectations, chimpanzees’ abundance appeared unaffected by human presence or settlements, be it used or abandoned. The primates were captured on camera in locations close to human settlements, sometimes carrying domesticated fruits like pineapples and mangos. However, the chimps foraged these sources of nutritious food early in the mornings and late in the day, appearing to time their visits to avoid contact with humans who were active in the same areas at midday.

The chimpanzees’ avoidance of the district’s roads stood out for several reasons.

Earlier studies in Central Africa (where a different subspecies of chimpanzee lives) suggested that chimps’ abundance was negatively affected only by the presence of tarmacked main roads, wider than 15 meters (50 feet), and relatively heavy traffic. But the study in Moyamba district found that chimpanzees avoided even the unpaved secondary roads here.

“This has a major implication when it comes to road infrastructure development, which is predicted to increase significantly in the coming years across Africa, including West Africa,” Humle said.

Other researchers in the field express similar concerns.

“This paper highlights that we need to better understand the impact of infrastructural development, such as roads, on chimpanzee distribution and behaviour, especially in light of the future road development across West Africa. It’s unlikely to be good news,” Kimberly Hockings, a conservation scientist at the University of Exeter, who was not involved in the new study, told Mongabay.

Hockings, whose research focuses on interactions between human and nonhuman great apes, said this and other research showing how some chimpanzee populations live in proximity to humans under certain conditions in no way justifies further destruction of ape habitat. “This needs to be made crystal clear,” she said.

The sensitivity of Moyamba’s chimps to even secondary roads has implications for governments in Sierra Leone and elsewhere in Africa, a region seeking to rapidly build much-needed infrastructure. Such infrastructure development can increase loss of habitat, as well as chimpanzee mortality, either directly through road kill or indirectly by enabling poaching, the study said.

Alongside care in planning infrastructure development, the research team would like to see local communities set aside areas in which fruiting trees, such as wild figs, can regenerate. “This could potentially help reduce chimpanzees reliance on crops for food. These areas would also benefit people when it comes to medicinal plants and other useful resources which they acknowledge are longer available due to forest loss,” said Humle.

“If we want to secure their long-term survival, it is crucial that successful protection measures should benefit people and chimpanzees alike,” Humle said. “Conservation actions should focus on education and helping farmers to implement alternative agricultural methods to slash and burn farming and environmentally-friendly revenue generating activities to ensure coexistence between the two species.”

Long-term solutions

Sierra Leone’s government says it is stepping up efforts to protect the chimpanzee. In March, it declared the western chimpanzee the country’s national symbol and promised to open two new sanctuaries for them.

But with the majority of the country’s chimpanzees living outside of protected areas, the creation of new refuges may be missing the point.

Lincoln Larson, an expert on human-wildlife interactions and conflict at North Carolina State University, U.S., argues that with the huge expansion of humankind’s ecological footprint, animals are forced to adapt or perish.

“This might mean occupying, and in some cases even thriving, in land dominated by human infrastructure,” he told Mongabay. “The chimps in Sierra Leone, the leopards in Mumbai, and the mountain lions in Los Angeles are all good examples of this.”

Species may change their behavior, patterns of activity, and even their diets to survive in human-dominated landscapes. But, Larson cautions, the consequences of these changes are unknown. “Confining wildlife to protected areas and/or waiting – hoping – for animals to adapt when they venture outside of parks are not viable ecologically or socio-economically viable options,” Larson says.

“To achieve coexistence, we must be proactive. We must search for creative solutions that support local livelihoods and community develop while simultaneously achieving conservation goals. And we must craft interventions that culturally compatible with the context in which a conflict emerges. All species might be at a crossroads at this point in time, but it is humans who determine where the path forward might lead.”

Banner image: Camera trap photo of a chimpanzee with mangoes. Photo: Tacugama Chimpanzee Sanctuary/DICE, University of Kent



Garriga, R. M., Marco, I., Casas-Díaz, E., Acevedo, P., Amarasekaran, B., Cuadrado, L., & Humle, T. (2019). Factors influencing wild chimpanzee (Pan troglodytes verus) relative abundance in an agriculture-swamp matrix outside protected areas. PLOS ONE, 14(5). doi:10.1371/journal.pone.0215545

Heinicke, S., Mundry, R., Boesch, C., Amarasekaran, B., Barrie, A., Brncic, T., … Kühl, H. S. (2019). Advancing conservation planning for western chimpanzees using IUCN SSC A.P.E.S.—the case of a taxon-specific database. Environmental Research Letters14(6), 064001. doi:10.1088/1748-9326/ab1379

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