Western Lowland Gorilla
Scientific Name: Gorilla gorilla gorilla
Scientific Name: Gorilla gorilla gorilla
While gorillas are the largest of all apes, western lowland gorillas (Gorilla gorilla gorilla) are the smallest of the three gorilla subspecies. The great apes also include the chimpanzee, bonobos and the orangutan. Male gorillas stand about 5½ feet tall and weigh around 300–450 pounds; females are only half the weight of males.
Western lowland gorillas are found in the tropical rainforests of West Africa, including southwest Nigeria, Cameroon, Rio Muni, Gabon and eastern Congo. Eastern lowland gorillas inhabit lowland forests over 625 miles away in eastern DR Congo. Mountain gorillas, the best known and most often studied race, are only found among the Virunga volcanoes of extreme northeastern DR Congo, western Uganda and northern Rwanda. They live on mountain floors and secondary forests with damp, hot climates, similar to a South Carolina summer.
Gorillas’ coats are black, brown or gray, with adult males having “silverback” saddles reaching to the thighs.
Hands, faces, feet and chests are black and hairless. Their skulls are large with heavy brow ridges. Noses are the most distinguishing features on gorillas, as individualized as fingerprints. Eyes are small and reddish brown in color. Ears are small and set close to the head. Like humans, gorillas have 32 teeth.
Gorillas have long arms, short legs and carry the bulk of their weight on their legs. They have short, broad hands with opposable thumbs that are adapted for “knuckle walking.” Of all the great apes, the gorillas’ feet are closest to those of humans, as the big and second toes are less opposable and are set closer together.
Gorillas are diurnal (active in the daytime) animals, living in groups of up to 30 with a single dominant male silverback. The groups, called troops, are well integrated and peaceful. Social grooming is common amongst troop and family members. Only silverbacks mate with females. Young silverbacks, known as bachelors, leave the group and live alone until they can coax away females of their own to form a troop. Females may move from group to group, but never live alone. Males nest on the ground, and females and their young nest on platforms built less than 10 feet from the ground.
Communication is accomplished both vocally and by full-body display. Over 20 different sounds have been recorded. Gorillas are more vocal during mating, and the silverbacks’ displays are well known. Males will beat their chests, make hoots and growls, put leaves between their lips as a symbol of feeding, stand upright and charge up to 20 feet before dropping to all fours. Gorillas also communicate through facial expressions and other body language.
Male gorillas reach maturity at eight to ten years of age, females at six to eight years. There is no fixed breeding season. Gorillas usually give birth to one offspring after a gestation period of about 8½ months. Babies generally stay with the mother until about age three, though they are weaned at two years. Females breed about every three to five years. Maternal behaviors are learned, not instinctive.
The median life expectancy for gorillas is estimated at 31 years for males and 38 years for females in AZA zoos; that is, 50% of gorillas that survive up to their first birthday will die before the median life expectancy and 50% will die after this age. The maximum longevity of gorillas born in zoos is 54 years for males and 57 years for females.
In the wild, gorillas feed on ground plants, leaves, bark, stems, roots, vines and bamboo. Sometimes young gorillas will climb trees and throw fruit down to older gorillas. Most water is taken from greens and fruit. Gorillas cannot swim and have been known to drown in relatively shallow water.
All gorillas, regardless of subspecies, are considered Critically Endangered under the IUCN, and wild born gorillas are banned from international trade by CITES (Conference on International Trade of Endangered Species). Under CITES, gorillas are considered to be Appendix I species and therefore receive the highest level of international protection, with about 100,000 gorillas remaining in the wild.
Threats to their survival include destruction of habitat and poaching. The lands in which they are found are poor and densely populated; park land set aside for gorillas is often encroached upon by agriculture. Wire traps set by poachers for other game often ensnare gorillas. Their heads and hands are prized trophies. Western gorilla populations also have been significantly affected by Ebola.
Western lowland gorillas are part of the Association of Zoos & Aquariums’ Species Survival Program (SSP). Under the SSP, zoos exchange gorillas so that suitable family groups can be formed. There are presently about 340 lowland gorillas in North American zoos. Since the first gorilla birth in a zoo in 1956, tremendous amounts of research on both captive and wild gorillas have revealed the social structure, habitat and nutrition requirements for successful breeding. Zoos are also working to allow as many infants as possible to be raised by their mothers instead of being hand-raised, so they can better learn natural gorilla behavior.
While zoos have made great strides in breeding gorillas in captivity, they have also worked to help gorillas in the wild, including adoption of a policy not accepting gorillas caught from the wild or “orphaned” gorilla infants. This practice serves to deter the illegal hunting of wild gorillas. In fact, no gorillas have been directly imported from the wild into North American zoos since 1972.
When they encounter gorillas, many people think of the well-known research by Diane Fossey, as featured in the film “Gorillas in the Mist.” It is important to point out that those are mountain gorillas, and the gorillas at Riverbanks are western lowland gorillas. However, research such as this has allowed zoos to advance their breeding capabilities so that no gorillas have been brought to US zoos from the wild since the 1970s.
Well-managed and well-presented gorilla troops in zoo settings offer a first-hand educational experience to millions of zoo visitors every year. Educational graphics such as those found in the Ndoki Base Camp serve to further entertain and enlighten visitors to the characteristics and plight of these amazing creatures. There are few other animal species that so easily excite the human spirit and imagination.