Great Apes and Humans: Hominidae

Physical characteristics: The western gorilla has short black hair with red or brown coloration on the top of the head. The face is black. The head is elongated, and a brow ridge sits over the eyes. A protruding belly houses a large intestine for processing a plant diet. The arms are very long, and the thick-skinned knuckles are used for walking. Big toes help grasp tree branches. At ages eleven to thirteen, males acquire silver-gray hair on their back, earning the name silverbacks. Males are bigger than females, averaging 352 pounds (160 kilograms) with a standing height of 5 to 6 feet (1.5 to 1.8 meters). Females weigh 150 to 251 pounds (68 to 114 kilograms), standing 5 feet (1.5 meters) tall.

The western gorilla is an herbivore, although young gorillas may eat termites and ants. (© Mark Newman/Photo Researchers, Inc. Reproduced by permission.)

Geographic range: Western gorillas are found in Angola, Cameroon, the Central African Republic, Congo, the Democratic Republic of the Congo, Equatorial Guinea, Gabon, and Nigeria.

Habitat: Western gorillas occupy open canopies and dense understories and forests that have been cultivated or logged. They inhabit swampy clearings, forests along rivers, and full-canopied primary forests.

Diet: Western gorillas prefer fruits but also feed on plants. In swamp forests, they eat water plants. Juveniles also eat termites and ants.

Behavior and reproduction: The gorilla family typically consists of a dominant male (silverback), a younger male, several adult females, and their offspring. The silverback protects the group, settles conflicts, and determines daily activities. The group forages on the ground, climbing trees only for special fruits or leaves. Members communicate using facial expressions, body language, and vocalizations. Females groom the silverback and mothers and infants groom each other, but other adults do not engage in mutual grooming. Gorillas build sleeping nests in trees, although heavier males nest on the ground.

The silverback mates with all receptive females, but adults of both sexes may have several partners. Females have single births every four years, nursing the young for three years. A young female leaves home to join a lone male or another group. She may change groups several times. A young male may inherit his father's position or leave home. When ready to reproduce, he will try to take over a group. If he succeeds, he kills the infants so that the mothers will be receptive to breeding. Scientists have found that males who stay in the neighborhood after leaving home have nonaggressive encounters, because they may be siblings or half-brothers and, therefore, have a familiar relationship.

Western gorillas and people: Western gorillas are popular in zoo exhibits. They are hunted for meat.

Conservation status: The IUCN lists the western gorilla as Endangered due to hunting, as well as habitat loss and degradation from agriculture, logging, and human developments. ∎