Cercopithecus solatus is a recently discovered monkey endemic to Gabon, present in parts of the Lopé National Park and the Forêt des Abeilles in the center of the country. It is listed as Vulnerable on the IUCN Red List (2010) due to its restricted extent of occurrence and continuing decline in population caused by high hunting pressure. All known field observations of this species are compiled here. Data collected since 1999 show that C. solatus occurs further to the south, east, and west than was previously known, and that its extent of occurrence almost certainly includes three national parks, rather than one.
Cercopithecus solatus was first described in 1988 (Harrison 1988), following sightings in 1984 in the Forêt des Abeilles, a large block of what was then mostly undisturbed primary forest in Central Gabon, north of the Ogooué River. Cercopithecus solatus is a member of the Ihoesti superspecies, and characterized by a bright yellow-orange on the distal half of its tail (Harrison 1988). The range of C. solatus is thought to be among the smallest of any African primate (Brugière and Gautier 1999). It was originally believed to be endemic to the Forêt des Abeilles forest block, but was later found in the contiguous Lopé Reserve to the west (White and Mackanga-Missandzou 1995). Cercopithecus solatus is threatened by hunting (Brugière and Gautier 1999), and being semi-terrestrial is sensitive to ground snares. Commercial hunting is likely to become a growing threat (Brugière and Gautier 1999), and could lead to population declines (IUCN 2010). Due to its restricted distribution, and the hunting pressure on the population, C. solatus is listed as Vulnerable on the IUCN Red List (IUCN 2010). It is also on Appendix II of CITES (CITES 2010), and was declared a fully protected species by the Gabonese government in 1994 (Brugière and Gautier 1999).
The range and habitat requirements of C. solatus have been further clarified since its original description in 1988 from the Forêt des Abeilles. In 1992, hunter surveys in 102 villages in the predicted range of C. solatus found that hunters did not encounter the species north of the Ogooué River nor west of the Offoué River. The species was not found south of the village of Popa, even though there was no obvious southern barrier (Gautier et al. 1992). In 1994, however, C. solatus was encountered in the center of the Lopé Reserve, west of the Offoué River (White and MackangaMissandzou 1995), providing the first sighting of the species in a protected area. Finally, surveys have shown that the density of C. solatus declines at higher elevations (Brugière et al. 1998), suggesting that the southern limit of the distribution may be limited by mountainous terrain—specifically by the lower density of the understorey (Brugière and Gautier, 1999).
In the last ten years, wildlife and bushmeat studies have been carried out in Central Gabon, both in and outside of protected areas. Many of these studies recorded sightings of C. solatus, either alive in the forest or as components of hunter catches. A collation of this data is presented here, which increases our understanding of the distribution of this species.
We contacted researchers working in Gabon, and asked them for any presence/absence information for C. solatus. We accepted presence/absence data from studies that used faunal transect surveys (visual and camera-trapping) inside and outside of protected areas, and from village bushmeat surveys and village interviews, as well as opportunistic sightings from experienced field researchers. Data on presence/absence of C. solatus were compiled (Table 1), and combined with data from the literature to create an updated range map (Fig. 1).
Sightings in and around Lopé National Park (Location Number (LN) 39–41, 61, Table 1)
In August 1995, a group of about 12 C. solutus were clearly seen by Kate Abernethy in trees next to the road in the SOFORGA logging concession. The observers (4) were on foot, and the monkeys travelled for several minutes in low vegetation near to the road. At one point an adult male walked several metres along a large branch in full view and was clearly identifiable, with the blue coloration of the scrotum easily visible. They were observed with 10 × 42 binoculars at a range of about 20 m. In 1993, on the road from Offoue to Booue, at the north-eastern border of the Lopé reserve, Lee White observed a group of 4 or 5 C. solatus on the ground crossing the road. The group was in clear view for 5 minutes, about 30 m from the vehicle. In 1994, Lee White met a hunter in Iwatsi village (close to the meeting-point of the Offoue and Onoy rivers) who had just arrived with an adult male sun-tailed guenon that he had shot. From 1989 to 2004, Kate Abernethy and Lee White carried out weekly transect surveys in the forest surrounding the Station d'Etudes des Gorilles et Chimpanzés, in the north of the Lopé reserve. No C. solatus were encountered during that time.
Sightings around the Makande study site (LN 29–38, Table 1)
A research camp (Makande), jointly run by the Institute for Tropical Ecological Research in Gabon (IRET) and the University of Rennes, hosted studies from 1992 to 1997 on the east side of the Offoué River. Much of the published literature on the species comes from this site or nearby.
Sightings during the “Megatransect expedition” (LN 41–45, Table 1)
The “Megatransect expedition” was a foot journey carried out between 1999 and 2001 by Mike Fay, from the northern Republic of Congo to the coast of Gabon. The trajectory passed through some of the most untouched forests remaining in Central Africa, and all wildlife and human sign was recorded along the way. Sun-tailed guenons were sighted on several occasions in October 2000, either in the Lopé Reserve (now Lopé National Park) or just to its southwestern border and at the limit of the Waka National Park (Fig. 1).
Sightings around Mount Iboundji (LN 47, 57, Table 1)
In the afternoons of 21 and 23 September 2001, Olivier Pauwels obtained good sightings of a group of 6–7 C. solatus feeding on a fruiting tree on the eastern slopes of Mount Iboundji (Offoué-Onoy Department, Ogooué-Lolo Province), in open forest, at an altitude of about 550 m. Using binoculars, he was able to identify the typical coloration of the species, and he approached the group until he was 60 m away. The species is well known by the villagers of Boussimbi, at the foot of the mountain (01°10′32″S, 11°49′16″E, altitude 485 m). They reported that C. solatus was common on the mount, and that groups often ventured into the village plantations.
Sightings around the Lekedi Sanctuary (LN 48, Table 1)
On 26 June 2003, Nicholas Bout radio-tracked a group of mandrills (Mandrillus sphinx) in the Lékédi Sanctuary. To search for the radio-collar signal he was positioned on a hilltop overlooking the canopy of the rainforest (approximately 01°47′05″S, 13°01′10″E). The position at the height of the canopy provided an unobstructed view of the forest. About 15 m from Bout, a slender and dark monkey, with a golden tail appeared and presented its profile on a large bare branch, offering a perfect view and was identifiable as C. solatus. It remained behind him for at least a minute. Seven monkeys also identified as C. solatus foraged in Pentaclethra macrophylla and Musanga cecropioides at 30 m above the ground in the canopy. They were not in the shadows, which allowed for good observation, and their long golden tails were clearly visible. The monkey closest to Bout suddenly rushed away and the group fled without calling. The entire group was counted—4 adults, 2 sub-adults and 1 infant. The local landscape is principally closed canopy forest with some forestsavannah mosaic, and is rich in all species of the local fauna found in southern and central Gabon, except the forest elephant (excluded from the sanctuary when it was fenced).
Village hunting returns in the Imeno Plateau and Ogooué-Lolo provinces (LN 46, 49, 50, 58, Table 1)
A study on subsistence hunting near logging concessions from 15 March to 20 June 2004 was carried out by Marielle Puit and local assistants in the villages of Iméno-Plateau (90-day survey), Mbégho (situated half way between Koulamoutou and Baniati, Lolo-Bouenguidi Department, OgoouéLolo Province; 45-day survey), and Roungassa (about 15 km northeast of Koulamoutou; 90-day survey). Observations were made in the eastern distributional limits of C. solatus; local villagers killed 10 C. solatus over 45 days in Mbégho (see Fig. 2). Six were shot, and four were caught by ground snares. Villagers of Mbégho mentioned that C. solatus had previously raided plantations. In 90 days in Roungassa, one C. solatus was shot (4 June 2004). During a previous hunting study carried out in 2000, Malcolm Starkey recorded that a sun-tailed monkey was killed by hunters in Banyati. Among the villages visited, Mbégho was the only one where the species was said to be abundant. It was said to be seen only occasionally in the others. Local vernacular names noted included bahia (Pouvi language, Mbégho), mbahi (Massango language, Iméno-Plateau) and imbonga (Nzebi language, Roungassa).
Village interviews and sightings along the Baposso-Mbigou road (LN 51, 59, 60, 62, Table 1)
Bushmeat inquiries were led by Jean-Jacques Tanga in several villages along the roads from Baposso to Mbigou (01°53′47″S, 11°54′37″E, altitude 700 m; Boumi-Louétsi Department, Ngounié Province), Mbigou to Koulamoutou (Lolo-Bouenguidi Department, Ogooué-Lolo Province), and from Koulamoutou to Pana (Lombo-Bouenguidi Department, Ogooué-Lolo Province), i.e., the three roads respectively situated near the eastern, northern and western limits of Mount Birougou National Park (February—March 2004, July 2004, June 2005). Main localities and park delimitations are shown by Anonymous (2002). The bushmeat markets of Koulamoutou, Mbigou and Pana were visited, and hunters from all the villages along these roads were interviewed and shown a poster illustrating 88 African primates (Kingdon 2001). These interviews show that the species was unknown in the villages situated west of the Onoye River (Moudouma, Itsiba, Mbigou and Lévinda), where the hunters did not recognize the species on the poster, and did not have a name to designate it. In comparison, the species was said to be present in the eastern villages (Léméngué, Koumbi, Siono and Grand Village), although uncommon, and always in small groups. In the villages in the northeast of Mount Birougou National Park, near Lolo River (Popa, Mambadi, Iwatsi, Missimba), the species was well known and was at once recognized both on the poster and on digital pictures. It was said to be locally common. In all villages where the species was recorded from Tanga's study, a single common name was given to this monkey by the Nzébi, Massango and Pouvi ethnic groups; mbaya, a name also used by the Massango in Iboundji area. In the villages near Lolo River, the species was well known for its habit of crop-raiding, especially manioc and bananas. It was hunted locally to reduce its impact on cultivated fields, and also as bushmeat. According to the interviews, it was most abundant in the hills between Lolo and Bouenguidi rivers. As these sightings are south of the formerly known distribution of C. solatus, Tanga asked the villagers to bring a specimen in order to unambiguously document irts occurrence. Popa villagers brought him a juvenile female in early June 2005 (Fig. 3). It had been caught in a ground snare in the northeastern buffer area of Mount Birougou National Park, in a hilly area (altitude 600 m). In the early afternoon of 8 March 2004, Tanga observed a single adult resting on a tree branch at the forest edge along the road between Popa and Mbigou Moréné (01°31′12″S, 12°17′24″E; altitude 355 m; Lolo-Bouenguidi Department, Ogooué-Lolo Province).
Camera trap study around Mount Mimongo (LN 52, Table 1)
During wildlife surveys conducted by Philipp Henschel between 14 April 2005 and 2 June 2005, C. solutus was photographed in a logging concession area south of Mount Mimongo (01°10′04″S, 12°08′29″E; altitude 675 m, Lolo-Bouenguidi Department, Ogooué-Lolo Province), a mountain range between Mount Iboundji and Mbégho. Seven images of C. solatus were obtained from 18 remote camera traps distributed through a 50-km2 study area over a 48-day trapping period (Fig. 4).
Camera trap study and hunting survey around the Lolo River (LN 63–64, Table 1)
Fifteen camera traps were deployed in a 30-km2 study area over 54 days between 28 August and 21 October 2004 in an area about 10 km to the south of the southern bank of the Lolo River. No images of C. solatus were obtained. This indicates that the species is either absent or very rare south of the LoIo River. Lauren Coad and local field assistants conducted a hunting study from January 2004 to January 2005 in the same area in two villages, Dibouka (01°19′07″S, 12°12′54″E) and Kouagna (01°18′28″S, 12°13′45″E). Their results showed considerable hunting pressure that was highest within 5 km from the villages, but also extended up to hunting camps 12 km to the north, on the southern bank of the Lolo. During this study all hunting returns for the two villages were recorded, and no C. solatus were ever caught or seen. During a previous hunting study in these villages conducted by Malcolm Starkey from 2000 to 2002, no C. solatus were observed or captured. Hunters from Dibouka could, however, identify C. solutus from Kingdon (2001) as mbaya, and said that it could be found around villages further south-west towards Iboundji.
Sightings between Popa and Ngoungou villages (LN 53, Table 1)
On 1 August 2006, in the forest surrounding Popa village, Yves Mihindou saw a single individual of C. solatus close to a group of C. nictitans in a Musanga cecropioides tree. As he approached, all the monkeys fled. This observation was made between the villages of Ngoungou (01°31′59″S, 12°19′09″E) and Popa (01°36′04″S, 12°18′14″E).
Sightings between Popa and Biroughou National Park (LN 54–55, Table 1)
In 2006, Yves Mihindou and Jean-Jacques Tanga reported separate sightings of individual sun-tailed guenons on the road from Popa to Birougou National Park, close to the northern boundary of the park.
It is clear that the range of C. solatus extends further to the west, south, and east than was previously thought, and the extent of occurrence may be as great as 18,000 km2 (previously the range was estimated at 11,000 to 12,000 km2; Brugière and Gautier 1999). Sightings of C. solatus very close to the limits of the national parks of Waka and Mount Birougou are particularly important, as the species was previously only known to occur in Lopé National Park. In addition, as both the Birougou and Lekedi areas are close to the Congolese border, it is possible that C. solatus may also occur in the Congolese part of the Massif du Chaillu. In that area of Congo, however, hunting pressure is considerably higher than on the Gabonese side of the border, and the single faunal survey carried out there in 2007 did not mention the species (Inkamba-Nkulu 2007). If present, the species is likely to be under considerable threat. The evidence from the Lolo area indicates that it may have been hunted to local extinction (as it occurs all around that area). The semi-terrestrial habits of the species render it vulnerable to wire snares, and when it encounters hunters with dogs it climbs and is then highly visible and vulnerable to hunters with guns.
Currently the IUCN Red List categorizes C. solatus as Vulnerable under the criteria Blab(v). The criterion B concerns the geographic range, and B1 specifically the extent of ocurrence, which, to qualify as Vulnerable, is considered to be less than 20,000 km2. To qualify as Vulnerable under criterion Bl, two further conditions (subcriteria) must apply in aspects concerning (a) a severely fragmented population or occurrence at no more than 10 locations, (b) decline in populations and range, or (c) extreme fluctuations in populations or range (see IUCN  for the precise criteria). In the case of the current designation, C. solatus was considered to exist at no more than 10 locations (a) and is suffering from decline in the numbers of mature individuals (b(v)) (Oates and Bearder 2008).
Oates and Bearder (2008) indicated that hunting was becoming an increasingly serious threat to C. solutus. Severe hunting pressure may be leading to local extinctions, and the number of mature individuals is undoubtedly decreasing. Most of the area of occurrence of the sun-tailed guenon apart from the protected areas is now under timber exploitation, with the result that the logging road network has penetrated almost all of its range. Roads provide easy access to local and commercial bushmeat hunters in the region and are strongly associated with wildlife depletion in Central Africa and in the range fragmentation of a number of species (Blake et al. 2008; Laurance et al. 2006; Minnemeyer et al. 2002; Stokes et al. 2010; Wilkie et al. 2000 ). Thus, the IUCN Red Listing status of the sun-tailed guenon should remain as Vulnerable Blab(v), despite the increase in the size of its extent of occurrence detailed in this paper.
Our field trips and research were financed by the UK National Environmental Research Council (NERC; LC), the Oxford Martin School (LC), the United States Agency for International Developent (USAID) through WCS-Gabon (JJT), the World Wide Fund for Nature Central Africa Regional Programme Office (WWF-CARPO; OSGP), the Wildlife Conservation Society (WCS; LJTW, MPS, FM, YM, NB, MF, PH), the UK Economic and Social Research Council (ESRC; MS), Fonds Français pour l'Environnement Mondial (MP), the University of Stirling (KA), and the Global Taxonomy. We are grateful to Dr Anne Franklin, Dr Yves Samyn and Dr Jackie Van Goethem (Institut royal des Sciences naturelles de Belgique (IRSNB), Brussels), René-Hilaire Adiaheno (Conseil national des parcs nationaux (CNPN)), Dr André Kamdem Toham (WWF-CARPO), Jean Massima (Popa), Luc Mathot (Liège), Bertrand Moundounga (Koulamoutou) and Matthew Steil (WCS-Gabon), the logging company SBL/TRB, the Project WWF/Nature+, the Centre International de Recherches Médicales de Franceville, and the villagers of Boussimbi, Popa, Dibouka and Kouagna. Dr. Sally A. Lahm (Institute for Tropical Ecological Research (IRET), Makokou), Dr. Allard Blom (WWF, Washington, DC), and Dr. Jean-Pierre Gautier (Université de Rennes) kindly gave useful comments on the manuscript.