Grauer’s Gorilla, Gorilla beringei graueri
Gorilla beringei graueri
Geographic Distribution and Habitat
Our earth’s largest primate, the Grauer’s gorilla (Gorilla beringei graueri), is found in the lowland tropical rainforests of eastern Democratic Republic of the Congo (DRC) in Central Africa. Its interrupted distribution extends from east of the Lualaba River, west through the Mitumba and Itombwe mountain chains, north to Mount Tshiaberimu in Virunga National Park, and south to the Fizi District of Hewa Bora region (home to a subpopulation). Kahuzi-Biega National Park and Oku Community Reserve are the heart of this great ape’s geographic range.
The habitat of this magnificent being includes the eastern Albertine Rift, a natural fracture in the earth’s crust that straddles the borders of the DRC, Uganda, Rwanda, Burundi, and Tanzania. This geologic, mountainous wonder is a key ecoregion for flora and fauna found nowhere else in the world.
These super-sized primates live across the widest altitudinal range of all gorillas, from about 1,968 ft (600 m) to 9,514 ft (2,900 m) above sea level. Indeed, while the vast majority of Grauer’s gorillas inhabit lower-elevation rainforests, two small populations have been reported in highland habitats.
Sadly, the war-torn conflict that has plagued the Democratic Republic of the Congo since 1996, related to Rwanda’s 1994 genocide, has largely diminished this great ape’s habitat to just one-fifth of what it once was. Illegal mining has also marred great tracts of habitat. Poaching has further jeopardized the species, leaving the Grauer’s gorilla on the brink of extinction.
The Grauer’s gorilla, classified as Critically Endangered, made its debut on the IUCN Red List of Threatened Species in 1996 as one of two subspecies of the Eastern gorilla (gorilla beringei); the mountain gorilla (gorilla beringei beringei), classified as Endangered, is the other.
Prior to its subspecies designation, Grauer’s gorilla had been referred to as the Eastern lowland gorilla, but this nomenclature is today regarded as a misnomer.
Size, Weight, and Lifespan
The Grauer’s gorilla is the earth’s largest primate, further distinguished from other gorillas by a stocky body, large hands, and a short muzzle. [Those other gorillas are Grauer’s subspecies cousin, the mountain gorilla, the Western lowland gorilla (gorilla gorilla gorilla), and the Cross River gorilla (gorilla gorilla diehli), each a subspecies of the Western gorilla (gorilla gorilla).]
Adult males weigh between 450 and 550 pounds (204–250 kg); however, giant-size male Grauer’s gorillas can weigh 600 pounds (272 kg) or more. Their maximum height is a towering 6 feet, 4 inches (1.95 meters).
Females weigh half as much as their male counterparts and stand only 5 feet, 3 inches (1.62 meters) tall or less.
The lifespan for the Grauer’s gorilla is 35 to 50 years in the wild.
Grauer’s gorillas look a lot like their mountain gorilla cousins, with subtle differences in appearance. Their slightly narrower physique and longer limbs are covered by a jet-black to blue-black fur coat with shorter hair on their head and body than mountain gorillas.
Like all gorillas, Grauer’s gorillas have a broad chest and shoulders, a large cone-shaped head (thanks to a bony crest at the top of the skull), and a shiny, black bare face that evokes an almost pensive expression. Dark eyes sit beneath a pronounced brow ridge, and a broad, flat nose with inquisitive nostrils, noticeably rounder than those of mountain gorillas, sit above a wide mouth with narrow lips. Tiny ears sit demurely on either side of their head. Ears, hands, and feet are bare; in old males, their chest is often bare of fur. As with other male gorillas, fully mature Grauer’s males sport a swath of silver-colored hairs down the center of their back, leading to the nickname “silverback.”
Their formidable size might lead to the assumption that Grauer’s gorillas are fierce predators. Not so. These extra-large primates are primarily plant-eaters, dining on at least 100 plant species. Stems, leaves, pith, bark, and roots are consumed, along with fruits. Fruit intake is highest during the wet season, from September to December when fruits are plentiful. A proclivity for figs has been recorded. And, on a seasonal basis, bamboo shoots are heavily consumed. Leaves, nuts, seeds, fungi, and herbs complement Nature’s meal plan for these great apes. A fraction of their mostly plant-based diet might contain the occasional insect, earthworm, or lizard.
Researchers have found that the diet of Grauer’s gorillas residing in lower-elevation rainforests differs from the two subpopulations residing in highland habitats. Studies were conducted between 2014 and 2020 in the Nkuba Conservation Area, a lower-elevation forest, 1,640–4,921 ft (500–1,500 m), between Kahuzi-Biega National Park and Maiko National Park in the DRC.
Delving further, researchers discovered that Grauer’s gorillas consume many of the same fruits as their eastern and western lowland cousins, whose environmental conditions are comparable to that of Grauer’s gorillas; other vegetative food that Grauer’s gorillas consume is similar to that of mountain gorillas who inhabit montane forests. The scientific conclusion is that variation in gorilla diets is linked to the variation of vegetation in their respective habitats.
Behavior and Lifestyle
Humans are not the only great apes who possess the trait of intelligence. We know that gorillas are intelligent, evidenced only in part by their ability to innovate. To more effectively gather food, they create rudimentary tools from their environment, using sticks to extract insect foods from tree holes.
Compared to their mountain gorilla cousins, whom researchers have heavily studied, less is known about the behavioral tendencies of Grauer’s gorillas. But observations of these great apes in certain situations may give insight. Like other great apes, Grauer’s gorillas exhibit behavior and emotions similar to humans—including empathy, curiosity . . . perhaps even grief. When members of a troop came across the corpse of an outsider silverback within their territory, they paused their activities to regard the body. Researchers present at the event, which occurred within the high-altitude sector of Kahuzi-Biega National Park, DNC, in 2016, recorded their observations.
For nearly 20 minutes, 17 of the troop’s 21 members circled the dead silverback, jostling their positions around the corpse, moving away, but straying no more than 10 m (33 ft), and then returning. They took turns inspecting, poking, and grooming the dead silverback. Some licked the body. Virtually all licked their own fingers after touching the corpse. Only one of the troop’s three adult females approached the corpse, carrying her two-year-old infant on her back. But she only stared; she did not touch the body. When the viewing ended, the troop’s resident silverback stood up on two legs. He beat his chest, charged the corpse, then hit the back of the dead silverback with his fists, before pushing the body down a slope.
Troop members’ varied responses to the deceased silverback led researchers to conclude that humans are not the only animals who respond to death in emotive ways. Further studies, researchers say, can help cultivate our understanding of how nonhuman animals perceive and process death.
Because of their enormous weight, these great apes spend most of their time on the ground, rather than in trees (making them “terrestrial” as opposed to “arboreal”). Should they decide to climb a tree, however, fully grown adults will keep to a tree’s thick trunk and large branches. Juveniles Grauer’s gorillas, who are lighter and more agile than their elders, are more likely to climb trees.
Gorillas are active during daylight hours, making them “diurnal.” Morning and afternoons are spent foraging and feeding, with time taken for a midday siesta. Rest breaks include mutual grooming sessions.
To travel, Grauer’s gorillas propel themselves through the forest quadrupedally (walking on all fours), while “knuckle-dragging”; that is, curving their fingers inward to support their weight on the ground they traverse. On occasion, they stand and walk upright.
As characterized by their well-developed social structure, troop members live closely with one another, interact, and travel together. In their search for food, Grauer’s gorillas cover vast distances.
Just before dusk, each gorilla begins gathering branches and leaves to create an elaborate nest in which to sleep overnight. Mothers and babies sleep together. Unlike chimpanzees, gorillas make their nightly nests on the ground.
Except for humans (who are the greatest threat to these great apes), Grauer’s gorillas’ formidable size dissuades most would-be predators. Only leopards and crocodiles pose a potential threat to the gorilla who is caught unaware.
Grauer’s gorilla is named after Rudolf Grauer, an Austrian explorer and zoologist who first recognized this great ape as a distinct subspecies.
Grauer’s gorillas are highly social animals who live in family groups, known as “troops,” led by a dominant silverback. Troop size ranges from 5 to 35 individuals, with the average troop size being 15 to 20. Besides the dominant silverback male gorilla, a troop typically includes at least three unrelated adult female gorillas and four or five of their young. Subordinate male gorillas may also be members of a troop.
Upon reaching puberty, subordinate males leave their natal (birth) group. They may spend a few months, or a few years, alone before these “solitary males” find a troop where they can install themselves as dominant male—or create a new troop by attracting females who have left an existing troop.
Females are known to leave their natal group when a troop’s dominant silverback dies. In fact, wildlife biologists have found that females might change groups several times during their lifetime in search of troops with a strong silverback male who will protect them.
But females don’t always leave home. A multi-female group and their offspring sometimes wait for a dominant silverback to find them and assume the role of their troop leader and protector. Wildlife biologists speculate that “safety in numbers” keeps the females and their offspring together.
Once a silverback has secured his place as the head of the troop, he remains with that troop for life—unless forced out by another male gorilla vying for the role of leader. By establishing an exclusive bond with each female, the likeliness that members of a dominant silverback’s harem will leave the troop or mate with another male gorilla is diminished.
Other endangered wildlife species who share the Grauer’s gorillas’ lush habitat in the DRC include mountain gorillas, golden monkeys, a subspecies of the owl-faced monkey, chimpanzees, bonobos, and forest elephants. Altogether, more than 400 species of mammal live here and 1,000 species of bird; 117 types of butterfly also make this ecoregion their home.
As with all gorilla species, vocal communication among Grauer’s gorillas is important. In all, 25 vocalizations—single-syllable and multi-syllable and each with its own specific meaning—have been observed. Captive Grauer’s gorillas have been taught to use sign language.
Infants typically emit whines and whimpers, chuckles or laughs accompany playtime between juveniles, and grunts or whimpers accompany copulation (mating) between adults. Several vocalizations are used in threatening situations: screams often indicate alarm; coughing grunts call attention to a mild threat, while “dog whines” indicate a more imminent threat; barks and hoots are emitted during threat displays and are often accompanied by intimidating postures and chest-beating—particularly by silverbacks.
As a tactile activity, allogrooming serves an important role in fostering and strengthening social bonds with one another.
While olfactory communication is not yet closely studied or documented for Grauer’s gorillas, other studies have shown that gorillas are able to discriminate among different odors, and they produce individually identified smells. In western lowland gorillas, olfactory communication—specifically, body odor, is known to be an effective communication tool. Researchers studying 13 individuals in the Central African Republic for 1 year found that body odors, varying in intensity according to the situation, accompanied the gorillas’ emotional responses to anger, distress, and danger. They further found that silverbacks communicate their status through the strength of their body odor; an especially pungent body odor sends a message to other males to keep away.
Females reach puberty at 9 years old, though do not usually give birth to their first child until age 10. Males lag behind a bit, reaching puberty at about 13 years old. But it will be some years before they sire their first young, not until they are between the ages of 15 and 20. This delay in fatherhood has more to do with strength and dominance than with biological capability. Only the dominant silverback is permitted to mate with the females in his troop, a key indicator of a polygynous society. Fights among dominant silverbacks for exclusive breeding privileges with mature female gorillas can be intense and result in the death of one of the male contenders.
Breeding season is throughout the year. Adult females give birth to a single infant about every 4 years, after a gestation period of 9 months (same as human primates). Infant mortality is high among helpless Grauer’s gorilla babies, who weigh a mere 4 pounds (1.8 kg) at birth. Many do not survive beyond their first 3 years of life.
Mothers are the primary caregivers. However, a troop’s silverback plays a supportive role in squashing any aggression or disputes from juveniles who might interfere with the females as they nurse their babies.
Baby gorillas learn to crawl at about 2 months of age; by 8 or 9 months old, they are walking. They are considered weaned at 2.5 to 3 years of age, at which time they become independent of their mothers.
Gorillas are considered to be an “umbrella” or “keystone” species who help to protect the biodiversity of their habitat, which they share with numerous other species—many of whom are also endangered.
As with other primates who have a largely frugivorous diet, Grauer’s gorillas are important seed dispersers, playing a critical role in forest regeneration in their fragile ecosystem. Because they travel great distances, they disperse seeds far from the mother tree, adding to the diversity of the forest flora.
The Grauer’s 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, assessed in September 2016, means that the species faces an “extremely high risk of extinction in the wild.” According to conservationists, the species has lost 77 percent of its population since 1994, falling from 16,900 to just 3,800 in 2015—a downward trajectory of 5 percent a year.
Political unrest, human encroachment, and degradation of Grauer’s gorilla habitat, including the prevalence of illegal mining camps (for tin, gold, diamonds, and, especially, coltan—an alloy used in cell phones), have all contributed to the population’s decline. The gravest threat against the species, however, is illegal hunting for the bushmeat trade. (These giant primates are also poached, “incidentally,” by those engaged in illegal mining activities.) The number of gorillas who are murdered annually for their flesh, however, is unknown. Gorillas are also captured, killed, and mutilated so their body parts can be fashioned into trinkets or for use in folkloric medicinal potions.
Orphaned baby gorillas who are the tragic victims of the bushmeat trade become victims again in the illegal pet trade. Over the past decade, Congolese wildlife authorities have rescued many of these baby gorillas. The babies’ parents had all been killed for meat. Sadly, most infant gorillas die without the care of their mothers. Attempts to introduce them into another wild gorilla troop have been unsuccessful.
Gorillas aren’t the only animals in the DNC who are being poached and slaughtered. Forest elephants are killed for their ivory tusks, with the overall population having plummeted by two-thirds.
The world’s climate crisis looms over the DRC’s tropical rainforests and the ecological wonder of the Albertine Rift. Recent climate models for the DRC show that nearly 50 percent of all mammals, birds, plants, and other species found nowhere else in the world will become threatened—or worse—by the year 2080. It’s possible that Grauer’s gorillas may forever disappear from the earth.
International trade of the Grauer’s gorilla is banned under its listing 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, this ban is largely ignored and difficult to enforce. For example, in theory, those gorillas living within the boundaries of Kahuzi-Biega National Park and Oku Community Reserve are legally protected. Congolese wildlife officials from the Institut Congolais pour la Conservation de la Nature (ICCN) oversee the protection laws, while Congolese park rangers risk their own lives to keep the gorillas safe from poachers. Sadly, over the span of two decades, nearly 200 of these courageous rangers, alongside the gorillas, have been murdered by heavily armed poachers.
Conservationists stress that improved and strengthened law enforcement—with an imperative of disarming lawless militia groups and poachers—is critical in saving Grauer’s gorillas.
Those conservation groups committed to saving the Grauer’s gorilla from extinction include the Rainforest Trust, Wildlife Conservation Society (WCS) DRC, and local Congolese partner Réserve des Gorilles de Punia (RGPu), who together established the Oku Wildlife Reserve. Encompassing more than 1 million acres, the reserve includes four adjacent community-managed local community forestry concessions in the buffer zone. RGPu’s help was instrumental in fostering a dialog with local tribal leaders to gain their support in developing customary rules that forbid hunting the gorillas while protecting the forests and biodiversity of community land.
The Itombwe Natural Reserve and the Punia Gorilla Reserve were established thanks to the persistent advocacy of conservationists and researchers. Although the national government had declared the Itombwe Natural Reserve as a protected area in 2006, its status was not formalized until 2016. Today, the reserve is divided into three zones: a conservation zone for wildlife with no human use; a multiple-use zone that allows limited human use and sustainable resource extraction; and a development zone that includes human villages where sustainable development projects are encouraged.
The Dian Fossey Gorilla Fund, dedicated to the conservation and protection of gorillas and their habitats in Africa, operates a permanent field station in Grauer’s gorilla habitat, providing direct protection for this now critically endangered species. Additionally, the Fossey Fund collaborates with government agencies and other international partners to provide assistance to local communities through education (including youth education programs), health, training, and development initiatives. Small-scale sustainable farm projects that help to decrease malnutrition and end bushmeat hunting are key community development efforts.
Other conservation groups include Fauna and Flora International (FFI) and the World Wildlife Fund (WWF).
The urgent situation for Grauer’s gorillas requires the concerted conservation efforts of all these global organizations and local groups. But if we are to keep this great ape from becoming extinct, we must expand our own humanity by recognizing our connection to this keystone species.
Some conservationists call for a public relations campaign akin to the “Blood Diamonds” campaign, which raises awareness of the environmental and human atrocities associated with harvesting these precious stones. A “Blood Coltan” campaign would raise awareness to the many gorillas murdered by miners in locations where the mineral coltan is illegally sourced.
- Plumptre AJ, Nixon S, Kujirakwinja DK, Vieilledent G, Critchlow R, Williamson EA, et al. (2016) Catastrophic Decline of World’s Largest Primate: 80% Loss of Grauer’s Gorilla (Gorilla beringei graueri) Population Justifies Critically Endangered Status. PLoS ONE 11(10): e0162697.
- https://newsroom.wcs.org/News-Releases/articleType/ArticleView/articleId/9247/Largest-Gorilla-Subspecies-Declared-Critically-Endangered-by-IUCN-Red-List.aspx https://pubmed.ncbi.nlm.nih.gov/34056732
Written by Kathleen Downey, 2016. Updated by author, January 2023