Population Structure

There are eleven known groups of Cross River Gorilla living in eight sites. Ten of these are clustered around the Nigeria-Cameroon border, and apparently form one large population, composed of three subpopulations that occasionally exchange migrants.

Although the forest between these groups has been worn away by human activity, satellite imagery shows that their ranges are still connected. The eleventh group is about 60km away, at Bechati-Fossimondi-Besali (13). It is unclear as yet whether the gorillas of this group are completely isolated, or if they maintain migratory links, however weak, with the rest of the Cross River Gorillas. (12)

In 2008, a survey team of the Environment and Rural Development Foundation (EruDeF) discovered eight gorilla skulls in local communities in the Bechati-Mone Forest Corridor. There are large parts of the forest which still have to be surveyed, in which there have been as yet unconfirmed reports of gorilla sightings by locals, so there may be undiscovered groups, and, potentially space for the known gorillas to expand into. (13)

Recently, gorillas were discovered in the Ebo Forest, Cameroon. These have not been classified into any of the existing subspecies, and may be a distinct type of gorilla. Further study will be necessary before we can be certain. (14)

Country/Site Status Altitude (m) Area (km2) Gorilla range (km2) Estimated Number
Afi Mountain Wildlife Sanctuary 130-1300 ~100 40 25-30
Mbe Mountains Proposed Community Wildlife Sanctuary 110-900 85 25 25-30
Okwangwo Division, Cross River National Park National Park 40-700 640 65 25-50
Takamanda National Park 80-1500 676 80 45-65
Mone River Forest Reserve 110-1200 538 35 20-30
Mbulu Unclassified 500-2000 ~1000 30 20-30
Kagwene Mountains Gorilla Sanctuary 1700-2000 19 19 20-30
Bechati-Fossimondi-Besali Unclassified 500-1200 ~25 ~25 20-30
TOTAL 200-295

Table adapted from Regional Action Plan (13) (updates from 15, 16)

The Ebo Forest Gorillas:

A recently discovered gorilla population at Ebo, is about 200km from the closest Cross River Gorilla site, and 100km from the nearest Western Lowland Gorillas. As with the remaining Cross River Gorilla groups, the Ebo gorillas are restricted to high, inaccessible ground. They are separated from the Western Lowland Gorillas by the Sanaga River, which is known to form a barrier between other sister species/subspecies, such as the moustached monkey to the south, and the red-eared monkey to the north. Mount Cameroon and the Bamenda highlands lie between the Cross River Gorillas and the Ebo forest, and may form another genetic barrier. Analysis of a skull from the Ebo population found that it did not fit into any of the common gorilla types in this region (Cross River Gorilla, Plateau Gorilla and Coast Gorilla). At this stage, any conclusions are just preliminary, but the Ebo Forest Gorillas may be a unique remnant of a type that was once more widespread in this region (17).