Monitoring Gorillas in Nigeria

Categories: Journal no. 40, Nigeria, Cross River National Park, Afi, Mbe, Cross River Gorilla, Gorilla Journal

Comparison of encounter rate of human sign (per km) in Boshi Extension, Mbe Mountains and Afi Mountain Wildlife Sanctuary (© Inaoyom Imong)

Comparison of encounter rate of human sign (per km) in Boshi Extension, Mbe Mountains and Afi Mountain Wildlife Sanctuary (© Inaoyom Imong)

From March to August 2009, surveys were conducted to evaluate the status of gorillas and other diurnal primates and their habitat at four gorilla localities in Nigeria. In this article, we present a summary of the survey results and make recommendations for improving gorilla conservation and management of the sites.

The surveys were conducted at three sites - the Afi Mountain Wildlife Sanctuary (AMWS), the Mbe Mountains Community Wildlife Sanctuary (MMCWS), and the Okwangwo Division of Cross River National Park (CRNP), where two gorilla localities (Boshi Extension and Okwa Hills) occur.
The "recce survey" method (White & Edwards, 2000; Kühl et al., 2008) was used at all sites. For the purpose of the surveys, each site was divided into smaller sectors for better coverage. The sectors were searched simultaneously at each site by teams of 3-4 persons.


Gorillas: A total of 74 gorilla nest sites were recorded; 33 of these were recorded in CRNP, 24 in MMCWS and 17 in AMWS. One of the objectives of these surveys was to obtain current gorilla population size estimates for the four localities in Nigeria (based on analysis of nest count data collected during these surveys) to assess the population growth trend. The estimates presented here are rough; obtaining accurate gorilla population size estimates from nest count data is difficult due to a number of factors, and the application of genetic methods to determine gorilla population size has shown that nest-based methods are liable to produce inaccurate estimates (Guschanski et. al. 2009).
The data suggest the presence of 25-35 gorillas in the AMWS, at least 20 gorillas in MMCWS, 11-23 gorillas in the Boshi Extension forest and 10-15 gorillas in the Okwa Hills during the survey period. These estimates are similar to estimates from previous surveys indicating that the gorilla populations at these sites have, remained stable over the last 5 years.
In AMWS fresh gorilla signs were limited to the north-eastern and south-central sectors of the sanctuary. No gorilla evidence was recorded in the north-western sector of the sanctuary, an area known to be used frequently by gorillas particularly during the dry season when fruit is scarce. The absence of any fresh or recent gorilla signs in that sector during the survey period (toward the end of the dry season in the Afi area) might be due to a recent bushfire that damaged large areas. In February 2008, one of the most severe wildfires since the creation of the AMWS occurred and affected the eastern, western and north-western sectors of the sanctuary. An earlier fire incident in 1997 damaged the northeastern part of the sanctuary and caused gorillas to abandon the sector for several years returning to the area only in 2005.
In MMCWS gorilla signs were concentrated within the south-central portion of the sanctuary (which forms the core of the gorilla range in the Mbe Mountains) during this survey, a pattern of distribution that has been observed in a number of previous surveys. No fresh gorilla evidence was found in the western sector of the Mbe Mountains, an area which was previously exploited frequently by gorillas. In February 2009, feeling aggrieved, 2 of the 9 surrounding communities that have traditional ownership of the Mbe Mountains resigned their membership of the recently established Conservation Association of the Mbe Mountains (CAMM) - the community conservation association that manages the sanctuary. To give maximum impact to their withdrawal from the association, the two communities banned all conservation activities in their part of the mountains, disrupting the research and anti-poaching activities of WCS ecoguards in that sector of the mountains. As a consequence of the absence of ecoguards in the sector, hunting and other illegal activities increased considerably, and this increased level of disturbance in the area might have caused the gorillas to temporarily move out of the area into less disturbed areas. Efforts led by WCS, with support from the Cross River State Forestry Commission, to resolve the disagreement in CAMM resulted in the lifting of the ban and resumption of research and anti-poaching activities in the sector.
In CRNP fresh gorilla activity was concentrated in the central portion of the Boshi Extension forest and in the eastern part of Okwa Hills close to the border with Cameroon. The gorillas inhabiting the Okwa Hills area have a transboundary range, moving across the border between the Okwa Hills in Nigeria and the Obonyi Hills area of the contiguous Takamanda National Park in Cameroon. As this survey focused only on the Nigerian side of the border, it is possible that the population size estimate given here may not be representative of the whole group, part of which might have been ranging in the Obonyi Hills in Cameroon, which was not searched during this survey. A brief reconnaissance survey which was limited to the Okwa Hills in April 2005 (NCF-WCS 2005) recorded a single nest site that contained 16 nests, but a recent survey of the Okwa Hills-Obonyi Hills transboundary area conducted in July 2008 (Imong & Warren 2008) estimated 1-3 gorilla sub-groups with a minimum population size of 16 individuals and a maximum of 33.

Other Diurnal Primates: Data from these surveys suggest the presence of at least two small chimpanzee (Pan troglodytes ellioti) groups in AMWS and at least one in MMCWS, at least one group in the Boshi Extension forest, and at least one group containing 7 individuals in the Okwa Hills. Their conservation status across all sites is thought to be precarious.
Evidence of drill presence was recorded at all sites, although disturbingly scarce in some. Drill (Mandrillus leucophaeus) signs were observed more frequently in the Mbe Mountains than at other sites. Estimated drill group size (based on foliage movement, dung, and litter disturbance) for MMCWS ranged from 30 to 60, although the number of individuals seen and counted during encounters ranged from 6 to 23. Drills were not sighted in AMWS, but other signs of their presence were observed. The data suggest the presence of 1-3 drill groups in AMWS and in MMCWS . In both the Boshi Extension and Okwa Hills areas of CRNP signs of drill were extremely scarce.
Olive baboons (Papio anubis) were recorded only in Boshi Extension where some savanna woodland habitat occurs on the northern fringes. Only a single observation (vocalization) of this species was made. Three guenons (Cercopithecus mona, C. nictitans and C. erythrotis) were observed to be more abundant in MMCWS and AMWS compared to Boshi Extension and Okwa Hills. The endangered Preuss' monkey was recorded only in Boshi Extension and Okwa Hills.

Human Disturbance: Illegal human activity was observed at all sites, but at a relatively lower frequency in MMCWS. Hunting pressure was particularly high in CRNP. Seven hunters and four active hunting sheds were recorded during the survey in addition to other evidence of hunting - gunshots heard, spent shotgun cartridges and wire snares. In AMWS, hunting and farm encroachment were major forms of human disturbance in addition to occasional bushfires. Hunting and farm encroachment in some areas were also the main forms of human disturbance in MMCWS.
At all sites, the presence of wire snares found in core gorilla areas is an indication that, although gorillas may not be targeted for hunting, they remain vulnerable since they are terrestrial and can get caught in snares with the possibility of sustaining potentially fatal injuries.


  1. Across all sites, but particularly in CRNP and AMWS, a more efficient ranger-patrol monitoring system should be developed to ensure that planned patrols are implemented; and all areas within the park and sanctuary are patrolled regularly to reduce levels of hunting and other forms of human disturbance that are currently widespread in both areas. The cybertracker system currently in use at CRNP and MMCWS is ideal for this purpose and better use of them is encouraged. Through the use of the cybertracker system, relatively good monitoring is already in place in MMCWS and seems to be yielding good results as reflected in the lower level of human disturbance in the sanctuary compared to CRNP and AMWS.
  2. Efforts to eliminate farms from AMWS should be intensified to curb the current high rate of farm encroachment. Ongoing discussions between the Cross River State Forestry Commission, NGO partners and local communities to agree a strategy to remove all farms from the sanctuary should be fast-tracked to ensure that the proposed farm elimination is achieved.
  3. The importance of the Olum Hills, adjoining the AMWS in the northeast, for gorillas and other species has long been recognized, a finding repeated by this 2009 survey. A review of the current AMWS boundary to include the Olum Hills is recommended.
  4. A rigorous annual fire prevention programme that includes cutting fire break trails in areas prone to bushfires around AMWS, and enactment and enforcement of stiffer laws against indiscriminate bush-burning, should be developed with local communities at all sites.
  5. At all sites, the development of a management plan that reflects current realities is recommended to ensure that management is based on a clear understanding of the area, its purpose, resources and values; provides guidance for day-to-day operations and planning, identifies monitoring needs and provides more efficient use of resources by prioritizing management activities.

Inaoyom Imong, Kathy L. Wood and Andrew Dunn

We are grateful to the Great Ape Conservation Fund of the United States Fish and Wildlife Service for funding these surveys.

Guschanski, K. et al. (2009): Counting elusive animals: comparing field and genetic census of the entire mountain gorilla population of Bwindi Impenetrable National Park, Uganda. Biological Conservation 142, 290-300
Imong, I. & Warren, Y. (2008): Survey of Gorillas and Other Large Mammals in the Okwa-Obonyi trans-boundary area of Cross River National Park (Nigeria) and the proposed Takamanda National Park (Cameroon). Unpublished report to MINFOF, the NNPS, USFWS, WWF and WCS Nigeria and Cameroon
Kühl, H. et al. (2008): Best Practice Guidelines for surveys and monitoring of Great Ape Populations. Gland, Switzerland: IUCN SSC Primate Specialist Group (PSG)
NCF-WCS Biodiversity Research Programme (2005): A Gorilla Reconnaissance Survey of the Okwa Hills, Okwangwo Division, Cross River National Park. Unpublished report to Cross River National Park, Nigerian Conservation Foundation and Wildlife Conservation Society. Research Report No. 3
White, L. & Edwards, A. (2000): Conservation research in the African rain forests: a technical handbook. The Wildlife Conservation Society. New York