WESTERN LOWLAND GORILLA

Gorilla gorilla gorilla

Geographic Distribution and Habitat
The western lowland gorilla is one of two subspecies of western gorilla (the rare Cross River gorilla being the other) and is the most widespread of all gorillas, inhabiting the dense and remote tropical rainforests of Cameroon, the Central African Republic, the Democratic Republic of Congo, Equatorial Guinea, Gabon, Angola, and the isolated lowland swampy forests of the Republic of Congo on the African continent. Their secluded habitats make it difficult for wildlife biologists to accurately determine how many of these great apes remain in the world, though the total population is thought to be close to 100,000 individuals.

Indeed, western lowland gorillas are more numerous than the other three gorilla subspecies including their Cross River gorilla “cousins” and the two subspecies of eastern gorilla: the mountain gorilla and Grauer’s gorilla, formerly known as the eastern lowland gorilla.

But like most gorillas, western lowland gorillas are Critically Endangered in the wild. (Although their population numbers are still small, the conservation status of mountain gorillas was reclassified to “Endangered” in 2018 because they are stable and carefully protected). Western lowland gorillas are also the gorilla subspecies most often found in zoos.

Western lowland gorilla geographic range in red. Map credit: Fobos92/Creative Common

Size, Weight, and Lifespan
Slightly smaller than the other gorilla subspecies, western lowland gorillas stand 4 to 6 feet tall (1.2 to 1.8m) and weigh between 150 and 440 pounds (68 to 200kg). Adult females are typically half the size of adult males. Lifespan in the wild is 35 to 50 years.

Appearance
Besides being a bit smaller than other gorillas, western lowland gorillas have shorter hair, longer arms, and a more prominent ridge line. They resemble their Cross River gorilla cousins but have a wider skull and smaller ears.

Like all gorillas, western lowland gorillas have flat, expressive faces with what appears to be a permanently furrowed brow (evocative of deep contemplation), wide nostrils, and dark eyes that are deeply set. Their faces, hands, and feet are bare of fur. The coats of western lowland gorillas are typically brownish gray, and they have auburn-colored chests; a reddish crest adorns their cone-shaped heads. Adult males sport a silvery swath of hair down their backs, a characteristic they share with all adult male gorillas, earning them the nickname “silverback.”

Diet
Their formidable size might suggest fearsome man-eaters, but these primate giants are predominantly vegetarian. They use their opposable thumbs to help them pick fruits from more than 100 varieties of fruit trees. In addition to these seasonal fruits, the diet of western lowland gorillas is comprised of roots, shoots, wild celery, tree bark, pulp, and nuts. Occasionally, especially in drier months when fruit is scarce, they might supplement their diet with termites or ants and the occasional lizard.

Behavior and Lifestyle
Foraging for all that fruit they eat takes western lowland gorillas over vast distances. Their preferred mode of locomotion is by walking on all fours, or “knuckle walking” (scientifically known as quadrupedalism); that is, they propel themselves forward by walking on the knuckles of their hands and on the soles of their feet. However, they are capable of walking upright—a feat that appears to be more of a swagger—for brief periods. This swagger might be accompanied by a display of chest-beating, if the situation warrants. To help them more effectively gather food, western lowland gorillas fashion rudimentary tools out of sticks and branches, useful in coaxing termites from mounds, for example.

Daytime is playtime for young gorillas. Like young human children (before they begin an obsession with cell phones and other electronic devices), gorilla youngsters spend a lot of time chasing one another, climbing trees, and swinging from branches. Gorilla moms and dads are simply too heavy to spend much time hanging out in trees with their children—their great girth would cause branches to collapse beneath them—so the treed rainforest habitat provides an awesome playground for gorilla youngsters. Besides, grownups need to spend their days foraging for their family so that everyone has plenty to eat.

When it’s time to go to sleep for the night, gorillas create nests out of the surrounding vegetation. They are skilled in this practice, constructing a new nest every night. Only infants share a nest with their mothers.

Fun Facts

Gorillas share 98.3 percent of their DNA with humans, making them our next-closest living relatives after bonobos and chimpanzees.

sad fact

Harambe, a western lowland gorilla at the Cincinnati Zoo, became known to the world when he was shot and killed by a zoo official, after a young child tumbled into the water-filled moat of the great ape’s enclosure in 2016. Video of the incident generated debate as to whether Harambe was trying to help or harm the child, when the great ape dragged the boy through the shallow moat in his habitat. The controversial killing of the great ape sparked outrage and sadness and led to conversations as to whether great apes belong in captivity. Harambe was killed one day after his seventeenth birthday.

Daily Life and Group Dynamics
Western lowland gorillas live in small, stable family groups known as troops. Of all the gorilla subspecies, theirs is the smallest troop size, consisting of four to eight individuals. Each troop is led by an alpha male, a silverback, whose job is to protect the troop’s members; he also has mating privileges and breeds with all the females in his group. A silverback retains his leadership position for years, and the adult females of his harem (who are unrelated to one another) usually remain with him for life.

About 50 percent of a group’s males and 75 percent of its females emigrate from their birth groups when they reach puberty. The males may travel for years in so-called “bachelor groups,” until they, themselves, become silverbacks and are able to establish their own groups by attracting females. Females put serious consideration in deciding which silverback they should join. A silverback’s leadership ability and the quality of his habitat are important factors in informing the feminine decision.

Occasionally, a lone silverback will infiltrate a group with the intention of deposing the reigning silverback and taking control of his harem. The ensuing silverback “throw down” is characterized by great posturing, elaborate displays of strength, hooting, chest-beating, and throwing sticks, branches, and vegetation at each other. On rare occasions, if intimidation fails to work, a fight to the death can result, with the victim most often being the lone male interloper. But fights are rare in gorilla troops. Most gorillas live peaceably with one another in their family group and in their interactions with outside groups.

Communication
Like all gorillas, western lowland gorillas employ a vast array of communications. Although they are normally quiet animals, their vocalizations include hoots, screams, barks, and roars, each with its own meaning. (Scientist have determined 22 different gorilla vocalizations.) Body language includes low crouches, an indication of submissiveness; and walking upright while beating their chests, as silverbacks do in the face of a threat.

Gorillas display behaviors and emotions similar to the human experience.

Captive gorillas have mastered simple human sign language.

Reproduction and Family
Female gorillas reach breeding age at ten years old. Males mature a bit later, not engaging in breeding activity before 15 to 20 years of age.

After a gestation period of about nine months, the same gestation period as human females, female gorillas give birth to a single infant (twins are rare). Newborns weigh a mere four pounds and can only cling to their mothers’ fur. At four months of age, they begin to ride on their mothers’ backs and continue this practice for the first two or three years of their lives.

Over the course of her life, a female gorilla gives birth about every four years. But infant mortality is high; only two or three of a gorilla mom’s offspring survive into adulthood.

Ecological Role
As with other primates who have a frugivorous diet, western lowland gorillas are important seed dispersers, playing a critical role in forest regeneration in their fragile ecosystem. Since they travel long distances, they disperse seeds far from the mother tree, adding to the diversity of the forest flora.

Conservation Status and Threats
The western lowland gorilla is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN. 2016), appearing on the IUCN Red List of Threatened Species. This highest threat level means that the western lowland gorilla joins most gorilla subspecies in facing an extremely high risk of extinction in the wild. 

Habitat loss through logging—clear-cutting the forests for agricultural use, mining (for coltan, a mineral used in cell phones), and for the development of human settlements—is the foremost threat against western lowland gorillas and other great apes. But logging leads to two other significant threats: poaching and disease.

Logging roads provide easy access for poachers to come into the gorillas’ habitat and kill them. But those doing the killing are not typically poor people from the indigenous community who hunt for survival. Rather, the poachers are professionals who kill the primates to sell their flesh, known as bushmeat, to gourmet food vendors who, in turn, sell the flesh as a high-priced delicacy item to affluent customers in city markets.

And with the influx of humans comes the spread of human diseases, including Ebola.

Poaching and disease have led to a 60-percent decline in western lowland gorilla populations over the last 25 years.

Gorillas are also killed so that their body parts can be fashioned into trinkets, charms, and various sundries for human use, such as an ashtray created from a gorilla hand.

Because of their large size, western lowland gorillas have few natural predators. Only large jungle cats and the occasional crocodile pose a threat.

Conservation Efforts
The western lowland gorilla is included under its parent species, the western gorilla (gorilla gorilla) in the African Convention on the Conservation of Nature and Natural Resources, listed under Class A; and listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.

However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce. Adding to their plight, nearly 80 percent of western lowland gorillas live in unprotected areas that are highly vulnerable to poaching.

But conservation groups dedicated to saving the western lowland gorilla from extinction are working to create effective law enforcement—not only in the protected areas of national parks but also in unprotected gorilla habitats. These groups, which include the World Wildlife Fund (WWF) and the Gorilla Organization, are brainstorming to develop effective and sustainable land use strategies that avoid destroying gorilla habitat. Maintaining large, intact, and well-protected areas of forest is key to maintaining great ape populations—and ensuring that they remain in the future of the world.

Carefully managed ecotourism allows visitors to view western lowland gorillas in their natural habitat, while raising much-needed funds for local communities.

Additionally, scientists are working to adapt the Ebola vaccine to help protect gorillas from this fatal disease.

The Bushmeat Conservation Task Force (BCTF) is a consortium of conservation organizations and scientists dedicated to the conservation of wildlife populations threatened by commercial hunting for sale as meat. Its goal is to eliminate the commercial bushmeat trade by raising awareness and building a public, professional, and government constituency aimed at identifying and supporting solutions that effectively respond to the bushmeat crisis in Africa and around the world.

References:

  • https://www.worldwildlife.org/species/western-lowland-gorilla
  • http://www.nationalgeographic.com/animals/mammals/w/western-lowland-gorilla
  • http://wwf.panda.org/what_we_do/endangered_species/great_apes/gorillas/western_lowland_gorilla
  • https://a-z-animals.com/animals/western-lowland-gorilla
  • http://www.iucnredlist.org/details/9404/0
  • https://www.stlzoo.org/animals/abouttheanimals/mammals/lemursmonkeysapes/westernlowlandgorilla
  • https://nationalzoo.si.edu/animals/western-lowland-gorilla
  • https://www.washingtonpost.com/news/animalia/wp/2016/06/02/what-harambes-death-means-for-a-critically-endangered-species-of-gorilla/?utm_term=.36e9efb6dacd
  • https://en.wikipedia.org/wiki/Killing_of_Harambe

Written by Kathleen Downey, March 2017