Western Gorilla

The western gorilla is the largest living primate and one of our closest relatives — close enough that we catch each other’s colds. It is also, despite being the more numerous of the two gorilla species, Critically Endangered.

Overview

There are two species of gorilla: the western gorilla of Central and West Africa’s lowland rainforests, and the eastern gorilla of the mountains and forests further east. Most western gorillas are the western lowland subspecies — the gorillas seen in zoos. They live in warm, wet, fruit-rich forest and swamp, moving through it in small family groups.

Physical characteristics

A mature male western gorilla stands up to 1.8 m and weighs as much as 200 kg, with an arm span wider than his height and a bite force among the strongest of any land mammal. Females are roughly half his size. Both walk on the soles of their feet and the knuckles of their hands — knuckle-walking — and can stand or run bipedally for short bursts.

Adult males develop the saddle of silver hair across the back and hips that gives them the name silverback, along with a tall bony crest on the skull that anchors huge jaw muscles.

Diet

Western lowland gorillas are bulk folivore-frugivores: the base of the diet is leaves, stems, and pith, but when fruit is available they seek it out and will travel long distances between fruiting trees. They also raid termite mounds and ant nests for protein. A silverback may process 18–30 kg of plant matter a day, and the group’s daily movement is largely a search for the next good feeding patch.

Society

Gorillas live in stable troops of about 5 to 30 animals: one dominant silverback, sometimes a second subordinate male, several adult females, and their offspring. The silverback is the centre of the group — females and young stay close to him, and he mediates conflict, chooses the day’s route, and builds a fresh nest of branches each night, as every gorilla over about three years old does.

When threatened, a silverback performs the famous display: hooting, throwing vegetation, running sideways, and beating his cupped hands against his chest to produce a sound that carries through the forest. It is almost always a bluff designed to avoid a real fight.

Reproduction and life cycle

Females give birth to a single infant after an 8.5-month pregnancy — about the same as a human — and nurse it for three to four years. Infants ride on the mother’s back, learn which plants to eat by watching her, and are fiercely protected by the silverback. A female raises only three or four surviving offspring in her lifetime.

Young females usually transfer to another troop when they mature; young males often leave to live alone for years before attracting females of their own.

Threats and conservation

The western gorilla is Critically Endangered and declining:

• Bushmeat hunting. Commercial poaching supplies urban meat markets and is the most immediate threat in accessible forest.
• Habitat loss from industrial logging, mining, and agriculture, which also opens roads that make poaching easier.
• Disease. Ebola has swept through Central African gorilla populations repeatedly, killing an estimated one-third of all gorillas since the 1990s.

Well-protected sites with tourism and anti-poaching patrols — and, for eastern gorillas, decades of intensive conservation — show that the decline can be halted, but western gorilla numbers are still falling across most of the range.