The Endangered West African chimpanzee Pan troglodytes verus is one of the most threatened subspecies of chimpanzee, with an annual decline of at least 4.7%; populations in its eastern range have been particularly vulnerable to local extinctions. Côte d'Ivoire has experienced a 90% population decrease over the past 20 years, and P. troglodytes verus is generally considered to be extirpated from Benin, Togo and Burkina Faso. Opinions in the literature are undecided, with inconsistent accounts and distribution maps. The 2003 IUCN Status Survey and Conservation Action Plan for West African Chimpanzees named the investigation of the presence of the chimpanzee in Burkina Faso as a priority, as did the 2005 World Atlas of Great Apes and their Conservation. Following an alleged sighting of a chimpanzee in south-eastern Burkina Faso in 2011, and based on unconfirmed reports of the subspecies in the south-west, our research team aimed to investigate the status of P. troglodytes verus in Burkina Faso.
Between 11 May and 16 July 2012 we conducted reconnaissance surveys totalling 250 km in five forest reserves along the southern border of Burkina Faso: Arly National Park and Pama Partial Reserve in the south-east, Comoé-Léraba Partial Reserve in the south-west, and Koulbi Protected Forest and Nazinga Game Ranch and Reserve in the south central region. While conducting a preliminary primate survey we searched for any signs of the presence of chimpanzees; we found no chimpanzee faeces, tracks, feeding signs or nests, and made no sightings, across the five study sites.
We supplemented our surveys with interviews with seven farmers, 12 forestry guides, and five forestry officials. We presented each participant with a series of animal pictures, only one of which was P. troglodytes verus, to control for bias, asking for a yes/no answer as to whether they had ever seen each animal in the wild. We were prepared to follow up on any potential leads with forest surveys but no new leads were acquired. Only three individuals reported ever seeing chimpanzees in Burkina Faso. Two reports came from the region of Arly National Park, from 1999 and 2002, respectively. The third report was from Comoé-Léraba Partial Reserve more than 13 years ago. The positions of Arly National Park and Pama Partial Reserve north of Benin and Togo, from which chimpanzees are considered to be extirpated, and the lack of knowledge of chimpanzees amongst forestry officials and guides, makes the south-east an unlikely habitat for chimpanzees. Our findings suggest that chimpanzees may have never occurred in the south central region of the country, including Koulbi Protected Forest, which is close to both Côte d'Ivoire and Ghana.
Comoé-Léraba Partial Reserve seems to have harboured seasonal populations of chimpanzees in the past, as reported in multiple sources for 1969–1988. These groups were probably moving north from Comoé National Park in northern Côte d'Ivoire, just 35 km south of Comoé-Léraba. We suggest that this seasonal behaviour has ceased and/or the regional population has dramatically decreased because of three inter-related reasons: (1) the high degree of poaching in Comoé-Léraba (we encountered signs of poaching at a rate of 0.29 km−1 surveyed); (2) the once well-protected Comoé National Park suffered a massive decline in its chimpanzee population after management was forced to leave the park during 2001–2011 during a period of political unrest; (3) the land between Comoé National Park and Comoé-Léraba is not protected or managed, leaving large mammals in the area extremely vulnerable to habitat loss and poaching.
We suggest that, although confirmation of absence can never truly be made, the perennial or seasonal presence of P. troglodytes verus in Burkina Faso is unlikely. This Endangered great ape has lost its foothold in Burkina Faso, Togo, Benin and Gambia, remains in only a small section of Ghana, and is experiencing a catastrophic population decline in Côte d'Ivoire. These findings highlight the continually shrinking range of the West African chimpanzee, which has been increasingly fragmented, and the species locally extirpated, over the past several generations.
