Distribution and Habitat Use of Gorillas in the Ebo Forest

Categories: Journal no. 65, Censuses, Rain Forest, Ecology, Cameroon, Western Lowland Gorilla

A view of the Ebo Forest (© Daniel Mfossa/ZSSD)

Although gorilla distribution and habitat use are fairly well known for many gorilla populations in Cameroon, very little is known concerning the Ebo population, probably one of the most threatened populations of western gorillas. The traditional threats to this isolated gorilla population include habitat loss and degradation related to settlement and subsistence farming expansion, logging and climate change. For example, in 2020, the entire Ebo forest was proposed for logging by the government of Cameroon. This led to protests and pressure from stakeholders including grassroots communities, leading to the suspension of the logging concession process. With no current legal conservation status for the Ebo forest, there is a continued risk that logging and other land use changes could threaten the local biodiversity.

Human signs recorded in the study area from 2013 to 2017

Human signs             Number
Used cartridge shells          340
Wire snares                         110

Cut marks or machete cuts   72
Used batteries                       52
Hunting trails                         51
Footprints                              21
Encounters                            21
Gunshots                               19
Hunting camps                      14
Vocalisations                           3
Abandoned logging roads       2
Other signs                             6
Total                                    711

Preliminary studies and informal interviews with local communities surrounding the Ebo forest from 2002 onwards suggested that the gorilla population is restricted to the north-eastern part of the forest. In our study from January 2013 to November 2017, we wanted to map the distribution of the gorilla population there and to assess habitat use mostly using indirect signs of gorillas including nests, faecal and feeding remains.

The study site (~39 km²) was identified from previous records of gorilla signs by the Ebo Forest Research Project between 2005 and 2011, and informal reports from local hunters. We used the recce survey method or random walks as opposed to line transect methods which facilitate future access by hunters and destroy more vegetation.

Recces involve walking in a predetermined direction, allowing for data collection on the spatial distribution of an animal population in remote areas by intentionally taking paths of least resistance which are permitted to deviate from the initial direction through the study area to some degree.

The study site is characterised by mature forest with sparse undergrowth and late successional large tree species. The forest canopy is generally closed (75-100 % covered), with minimal sapling undergrowth. Primary and very old secondary forest falls into this vegetation category.

Secondary forest covers areas affected by recent or old anthropogenic activities (logging, abandoned plantation or habitation) with the canopy moderately closed (50-75 % covered) or open (25-50 % covered), a relative dense ligneous and/or herbaceous undergrowth and presence of indicator trees or scrubs.

Grassland covers areas ranging from 50-3,000 m² with scattered young trees and/or shrubs. In this vegetation category the canopy is open (25-50 % covered) or very open (0-25 % covered), and the dense or very dense herbaceous undergrowth is sometimes dominated by ferns and plants in the families Marantaceae and Zingiberaceae.

Swampy areas cover hydromorphic soil seasonally or permanently flooded, with a mixture of species principally characterised by high densities of hydromorphic plants and some water-adapted shrubs or trees.

Over the study period we surveyed 1935.8 km of recces in the study area and detected evidence of gorilla presence on 261 occasions. Based on the distribution of gorilla signs across the forest, the total estimated distribution of the population covered ~22 km² and was restricted to the central band of the study area. Both overall and for each season, gorilla signs were concentrated in the northern part of the study area. We observed a slight seasonal variation, with gorilla signs being more clumped during the dry season compared to the rainy season. Except for the southwestern part of the study area, evidence of human activities was prominent across the study area, including within areas with a high gorilla presence.

Mature forest was the most common habitat type throughout the study area (87.04 % coverage of the total), followed by secondary forest (7.90 %). The extent of grassland and the swampy areas were comparable and covered 2.63 % and 2.43 % of the area respectively. Gorilla signs were recorded in the four main habitat types found in the study area; more than half of the signs were observed in the grassland (53.6 %) followed by the mature forest (37.9 %). Very few signs were recorded in swampy areas (5.6 %) and secondary forest (2.8 %).

These results suggest that gorillas used grassland more than expected (53.6 % of signs yet only 2.63 % coverage) and mature forest less than expected (37.9 % of signs yet 87.04 % coverage). Gorillas tended to use the swampy areas more often during the dry season (57.14 %), while they visited the secondary forest most during the rainy season. Other studies have revealed that gorillas show a preference for light gaps in the forest which provide them with a variety of herbaceous and fruiting plants as food sources and preferred nest-building materials.

The Ebo gorillas ranged over around 22 km² and were restricted to the central band of the study area. This result concurs with an earlier study which suggested that the gorillas may have a very limited distribution within the Ebo forest.

Although the indirect human impact on the Ebo gorilla population still needs to be investigated systematically, the situation here could be less catastrophic than elsewhere, since gorillas are not currently targeted by hunters, at least partly due to sensitisation campaigns carried out by the community conservation association 'Clubs des Amis des Gorilles' (Gorilla Guardian Clubs) since 2012. This concurs with previous studies that have demonstrated that consistent conservation activities in local communities positively influence the preservation of wildlife species.

Further studies using alternative survey methods are essential to determine accurately the population size and dynamics, to shed light on the status of this population, and to clarify its taxonomic status through genetic studies. We recommend promoting and supporting sustainable alternative livelihood projects for the benefit of the local population that should, if implemented appropriately, reduce pressure on the gorilla habitat.

Daniel Mbouombouo Mfossa, Ekwoge Enang Abwe and Bethan J. Morgan

Original publication
Mfossa D. M., Abwe, E. E., Whytock, R. C., Morgan, B. J., Huynen, M.-C., Beudels-Jamar, R. C., Brotcorne, F. & Tchouamo, R. I. (2022): Distribution, habitat use and human disturbance of gorillas (Gorilla gorilla) in the Ebo forest, Littoral Region, Cameroon. African Journal of Ecology 00, 1-13