Status & Distribution

The geographic range of western chimpanzees, Pan troglodytes verus, spans eight West African countries and a diverse array of habitats, from the tropical humid forests along the coast to the montane regions of Nimba and Lofa, north to the undulating highlands of the Fouta-Djallon, and the savanna mosaic that touches the Sudano Sahel. Humans and chimpanzees have coexisted in this region for thousands of years. While the human population has exploded in size in recent years, the chimpanzee population has declined precipitously, and been extirpated through a large part of its former range. In the past two decades, the number of chimpanzees in West Africa has declined by 80% – a trajectory that will continue unless concerted action backed by local, national and international support is taken immediately.

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Current knowledge of chimpanzee distribution in West Africa

Pan troglodytes verus occurs in eight countries: Côte d’Ivoire, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Senegal and Sierra Leone.

 

Chimpanzees have already been extirpated from Benin, Burkina Faso and Togo (Ginn et al. 2013; Campbell & Houngbedji 2015); Ghana may soon be added to this list, as only a small number of individuals remain in the southwest of the country.

Guinea, Liberia and Sierra Leone are the strongholds of this subspecies, harbouring the largest chimpanzee populations in the region. In Côte d’Ivoire, their numbers have declined by 80% since 1990 due to anthropogenic pressures and land conversion, corresponding to a range contraction of 20%. Only a few hundred remain in two national parks, Taï and Comoé (Campbell et al. 2008; Granier et al. 2014

Data on the range limits in Guinea-Bissau, Mali and Senegal are scarce. Recent information indicates that the northern limits are likely near Hérémakhono, Senegal (Wessling et al. 2019, Wessling et al. 2020). Surveys in Senegal indicate that chimpanzees are widespread, although there is some discrepancy between modelled estimates and previously published estimates. In Mali, the chimpanzee’s range limits remain unclear and no surveys outside Bafing and Moyen-Bafing national parks have been undertaken since 2004 (Duvall 2008). The widespread distribution of chimpanzees in Guinea-Bissau has been confirmed (Carvalho et al. 2013; Bersacola et al. 2018), although population trends could not be derived due to a lack of historical estimates.

Current and previously known geographic range of western chimpanzees
Based on Kühl et al. 2017 (map: Tenekwetche Sop)

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Alarming decline of western chimpanzees in Côte d’Ivoire

One example of a country in which western chimpanzee loss has been extensively and closely monitored over time is that of the unprecedented and exceptional decline of chimpanzee populations in Côte d’Ivoire. It was once home to likely one of the largest western chimpanzee populations, but natural habitat in most of the country has been lost to the industrial agricultural sector (for example, for coffee, cacao, palm oil). Now chimpanzees are largely found only in two national parks: Taï and Comoé. These two parks likely harbour only a few hundred individuals, whereas remnant populations outside park boundaries hang on with less than 100 individuals. Similar declines have occurred even in protected areas, such as the Marahoué National Park, where chimpanzees were extirpated in just a few years because of inadequate law enforcement, lack of immigration controls and poor park management. As such, the chimpanzee range in Côte d’Ivoire has been reduced by 70.3% (T. Sop, pers. comm.), and an analysis of chimpanzee population patterns in the country suggested already dramatic declines by 2008. These declines appear to have continued into 2014, despite longstanding and extensive efforts made to conserve this species in Côte d’Ivoire, demonstrating the difficulty in mitigating ongoing threats to chimpanzee populations in the region.

Current and previously known geographic range of chimpanzees in Côte d’Ivoire, highlighting sites where chimpanzees have been extirpated.
Based on Campbell et al. 2008 and Kühl et al. 2017 (map: Tenekwetche Sop)

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Population estimates

The IUCN SSC Ape Populations, Environments and Surveys database (hereafter A.P.E.S.) was established in 2005 (Kühl et al. 2007). This repository now includes many survey datasets (listed in Sop et al. 2018), including the Guinean section of Fouta Djallon, and national datasets for Côte d’Ivoire, Liberia and Sierra Leone. Combining local surveys with large-scale surveys allows estimates to be projected for unsurveyed areas and informs on general patterns at a larger scale. At the regional scale, Kühl et al. (2017) compiled abundance data from 35 sites to estimate population trends and geographic range for western chimpanzees, and Heinicke et al. (2019a) compiled 52 density surveys to model the density distribution of western chimpanzees.

Modelled density distribution of western chimpanzees across their range
(reproduced from Heinicke et al. 2019a, CC BY 3.0)

Figure 2-3 Modelled density distribution (reproduced from Heinicke et al. 2019a, CC BY 3.0

Important conservation areas

To support systematic conservation planning for western chimpanzees, Heinicke et al. (2019c) used the modelled chimpanzee density distribution and a spatial prioritisation algorithm to identify important geographic areas for conservation of the subspecies. Based on scenarios that account for different spatial scales and conservation targets, the study identified Fouta Djallon and 14 transboundary areas shared by Côte d’Ivoire, Guinea, Liberia and Sierra Leone as being particularly important. While there was a strong overlap with priority areas identified in the first regional action plan for this subspecies (Kormos & Boesch 2003), the analysis highlighted the importance of the north-south connectivity across the chimpanzee’s range from southern Senegal to northern Sierra Leone. The areas mapped areas are presented here to inform stakeholder consultation processes, such as the expanding a PA network, identification of priority sites, the designation of “no-go” zones for industry and infrastructure projects, and where to target conservation activities outside PAs. For countries with small chimpanzee populations, especially Ghana, scenarios run separately for each country will be more informative for determining where conservation activities should be targeted. Further information is available via the IUCN SSC A.P.E.S. database.

 Important conservation areas for western chimpanzees
with the number of times a cell was selected summed up across 27 scenarios overlapping the Kormos and Boesch (2003) priority areas for (a) Comoé, (b) Diéke, (c) Fouta Djallon, (d) Ghana-Côte d’Ivoire border, (e) Guinea-Guinea-Bissau coastal, (f) Haute Sassandra and Mt Péko, (g) Haut Niger, (h) Lofa-Mano-Gola forests, (i) Loma mountains, (j) Manding plateau, (k) Marahoué, (l) Nimba mountains, (m) Outamba-Kilimi and Guinea border, (n) Taï-Grebo-Sapo-Cestos, (o) Ziama and Wonegizi
(reproduced from Heinicke et al. 2019c, CC BY 3.0)

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