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Western chimp numbers revised up to 53,000, but development threats loom

Western Chimpanzees at Tacugama Chimp Sanctuary in Freetown, Sierra Leone. Photo by BigMikeSndTech, licensed under CC by 2.0

Western Chimpanzees at Tacugama Chimp Sanctuary in Freetown, Sierra Leone. Photo by BigMikeSndTech, licensed under CC by 2.0

  • A new survey of data from the IUCN’s Apes Database indicates that there are nearly 53,000 western chimpanzees in West Africa.
  • The number is significantly higher than previous estimates, which placed the population closer to 35,000, but the subspecies remains categorized as critically endangered on the IUCN Red List.
  • The authors of the study say their findings can help governments in the region ensure that proposed infrastructure projects do as little harm to the remaining chimpanzee populations as possible.

Nearly 53,000 western chimpanzees live in the forests and savannas of West Africa, a higher number than previously thought, according to a new study published in the journal Environmental Research Letters.

The study finds that just 17 percent of this population lives inside high-level protected areas, and points to a series of proposed development corridors as among the potential threats to chimpanzee populations in the region.

Earlier estimates placed the population of western chimpanzees (Pan troglogytes verus) at closer to 35,000. Drawing on a larger number of surveys included in the IUCN database for the subspecies, the authors of the latest study say they were able to more accurately estimate both population and distribution.

Set up to encourage researchers to share their findings with one another, the IUCN database has proved vital in providing conservationists and policymakers with a sharper picture of ape populations in West Africa and elsewhere. Three-quarters of the studies used to develop the new population estimate for western chimpanzees are unpublished; Stefanie Heinicke, a researcher with the Max Planck Institute for Evolutionary Anthropology and lead author of the survey, said the census would not have been possible without the database.

“Because we were able to use so many datasets shared by the collaborators with the IUCN SSC A.P.E.S. Database, we were now able to for the first time model the western chimpanzee density distribution across their entire range, including unsurveyed areas,” she told Mongabay in an interview. “This explains why our estimate is higher.”

Findings contained in the database, for example, allowed the authors to revise estimates for the western chimpanzee population in Senegal up from a few hundred to around 2,600. The new study will better equip governments in the region to understand how development corridors and other infrastructure investments can be designed with conservation of this population in mind.

Nearly 11,000 kilometers (7,000 miles) of foot surveys were carried out between 2001 and 2016 to gather the data presented in the report.

“The datasets used in this paper came from 58 separate surveys in different places across the range of the species,” Fiona Maisels, a co-author of the paper, told Mongabay. “They are all nest count surveys, which means that researchers walk a series of lines within each of the areas surveyed looking for chimp nests.”

Guinea holds largest population

The study focused on the critically endangered western chimpanzees, one of four chimpanzee subspecies. They are found to the west of the Dahomey Gap that separates Central African forests from those in West Africa.

The largest population of western chimpanzees was found in the Fouta Djallon region of north-central Guinea, where cultural taboos against hunting chimpanzees are strong and industrial-scale economic activity is low compared to other parts of the region. The study indicates that just over three-quarters live in “savanna-mosaic forests,” with the rest living either in dense rainforests or, more rarely, cropland habitats.

While the new census figure is higher than previous estimates, western chimpanzees remain in peril. A 2017 study calculated that their numbers had declined by a staggering 80 percent since 1990. Even with the upward revision, the subspecies remains categorized as critically endangered on the IUCN’s Red List, or just one step away from being extinct in the wild.

The majority of western chimpanzees were said to be living in relatively close proximity to human activity: 67 percent within 10 kilometers (6 miles) of human settlements, and 88 percent within 10 kilometers of roads. The study suggests that plans for further development — including mines, dams and a series of planned development corridors that would extend roads, irrigation and other infrastructure in the western chimpanzee’s range — could pose dangers to the region’s remaining population.

Development projects a potential threat

The number of western chimpanzees in Ghana and Côte d’Ivoire plummeted due to large-scale deforestation and widespread hunting linked to the expansion of industrial agriculture. The study used data on four proposed development corridors to show how they could threaten remaining chimpanzee populations, particularly in cases where new roads would cut through high-density habitats. Development of infrastructure there and in other areas where western chimpanzees live could lead to further declines in their numbers.

Workers marking cut logs on a road in a forestry concession in Rivercess County, Liberia. Photo by Flore de Preneuf/PROFOR, licensed under CC BY-NC 2.0
Workers on a forestry concession in Rivercess County, Liberia. Photo by Flore de Preneuf/PROFOR, licensed under CC BY-NC 2.0

Policymakers and leaders in the region view development corridors as a means of lifting rural citizens out of poverty and integrating the economies of neighboring countries. But according to the study, just over 10 percent of the remaining western chimpanzees in the region live within 25 kilometers (16 miles) of the four proposed corridors.

One would link the Guinean capital of Conakry to the Liberian port city of Buchanan, in the process bisecting a series of dense forests along border areas in the two countries. Some of those forests contain large western chimpanzee populations, raising fears that increased economic activity would also raise demand for bushmeat and damage habitats the animals rely on. Researchers say they hope the study will help give policymakers a tool to reduce the impact of infrastructure development on the subspecies.

“What we can do now is identify if these corridors are cutting through high-density areas for chimpanzee populations, so this is really about informing land use and conservation planning,” Heinicke said. “For example, one could redirect planned roads to avoid these areas.”


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 Letters. doi:10.1088/1748-9326/ab1379

Banner image: Western Chimpanzees at the Tacugama Chimpanzee Sanctuary near Freetown, Sierra Leone. Photo by BigMikeSndTech, licensed under CC by 2.0


Correction: An earlier version of this article incorrectly stated the estimated western chimpanzee population in Senegal is nearly 6,000; in fact the study estimates this population to be around 2,600. 


Ashoka Mukpo is a freelance journalist with expertise in international development policy, human rights, and environmental issues. His work has been featured in Al-Jazeera, Vice News, The Nation, The Guardian, and elsewhere. Follow him on Twitter at @unkyoka.

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