Behaviour & Ecology

Socio-ecology and Behaviour

Cross River Gorillas typically live in small groups of four to seven individuals, though larger groups do occur. The best-studied group at Afi consists of around 18 gorillas that range across approximately 30 km²—a larger home range than is typical for Western Lowland Gorillas. Over a three-month period, the group follows a cyclical movement pattern, shifting how intensively different areas are used based on seasonal food availability and perceived predation risk.

At Afi, the gorillas sometimes split into temporary foraging subgroups for one or more days—particularly when feeding on widely scattered fruits and herbs—and then reunite as a larger group during resting periods.

Similar flexibility has been observed at Kagwene, where nest group sizes vary widely, suggesting fluid grouping patterns. Gorillas here occupy an area of roughly 19 km², with an average daily travel distance of about 1 km at both sites. At Afi and Kagwene, gorillas more frequently build their nests in trees than has been reported for Western Lowland Gorillas.

Cross River Gorillas have also been observed throwing clumps of earth or branches toward humans—a behaviour rare in gorillas and more commonly associated with chimpanzees.

Tool-Use Observations

Of the six recognised categories of tool use in primates, one has been documented in Cross River Gorillas. On three occasions at Kagwene, gorillas threw earth or branches toward people. In one instance, researchers observed a man initiate the interaction by throwing stones at the gorillas, raising the possibility that the behaviour was learned in response to human disturbance.

Because Cross River Gorillas live in unusually close proximity to people, such defensive or deterrent behaviour may reflect local adaptation rather than widespread gorilla behaviour.

Habitat of the Cross River Gorilla

Cross River Gorillas inhabit the Cross River region of Nigeria and Cameroon and the Lebialem Highlands—an area separated from the vast western equatorial forests by the Sanaga River and expanding agricultural land.

The region has a more strongly seasonal climate than other gorilla habitats, with a longer, drier dry season and heavier rainfall during the wet season. The landscape is rugged and mountainous, characterised by steep valleys, cliffs, and narrow ridges. Elevation ranges from 200 to 2,037 metres, but the gorillas largely occupy remote highland areas, where human disturbance is lowest.

They show no strong habitat preference within their range and are believed to have been pushed into these fragmented refuges by historical hunting pressure. Sightings suggest seasonal altitudinal movements—gorillas tend to shift upslope during the wet season and descend into valleys in the dry season.

Across the region, moist lowland rainforest rises into sub-montane forest at 700–800 m, transitioning to montane forest above 1,500 m. Parts of Cross River National Park protect a rare continuum of all three forest types. While extensive primary forest still exists, several gorilla groups live in small and isolated forest patches, linked only by narrow and vulnerable corridors.

Human settlement is widespread and expanding. The lowlands form a patchwork of farmland, plantations, grassland, and secondary forest, intersected by villages and roads. Any gorilla migrating between groups—or ranging beyond usual feeding areas—must navigate through this fragmented human-dominated landscape, increasing risks and limiting natural movement.

Diet of the Cross River Gorilla

Cross River Gorillas rely more heavily on lianas and tree bark year-round and consume less fruit during periods of scarcity than Western Lowland Gorillas. In Afi, gorillas travel longer distances when feeding on fruit, whereas in Kagwene, daily travel distances are shorter when fruit is abundant.

When food is scarce, gorillas may leave their usual home ranges, either to explore other parts of the forest or to venture into lowland areas. This can sometimes bring them into conflict with farmers, as gorillas may feed on crops such as plantains and bananas. However, gorillas are not the most destructive species in the region; small mammals and larger animals like wild pigs often cause more agricultural damage.

Human-Wildlife Conflict

Crop-raiding by gorillas can seriously affect individual farmers, particularly when plantain or banana stands are damaged. For example, in January 2006, six farms across two villages near Afi reported gorilla-related crop damage—an event that locals said had not occurred in the previous 20 years.

Such incidents are often influenced by a combination of factors, including seasonal food scarcity, proximity of farmland to forest, and improved protection of gorillas from hunting. These occasional conflicts highlight the importance of including local communities in conservation planning, ensuring that both gorillas and people can coexist peacefully.