Gorilla beringei graueri
Geographic Distribution and Habitat
Grauer’s gorilla, formerly known as the eastern lowland gorilla, is found only in the lowland tropical rainforests of eastern Democratic Republic of Congo in Central Africa. One of two subspecies of the eastern gorilla (the mountain gorilla is the other), Grauer’s gorilla is Earth’s largest primate. 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 Democratic Republic of the Congo, Uganda, Rwanda, Burundi, and Tanzania. This geologic, mountainous wonder is a key ecoregion for flora and fauna found nowhere else in the world. The species’ historic range extends towards Punia in the west, from the Lindi River in the north, and to the Itombwe Mountains in the south.
But the war-torn conflict that has plagued the Democratic Republic of Congo since 1996, related to Rwanda’s 1994 genocide, has largely destroyed this great ape’s habitat. Illegal mining has also marred great tracts of habitat. Poaching has further jeopardized the species, leaving Grauer’s gorilla on the brink of extinction.
Size, Weight, and Lifespan
The earth’s largest primate is distinguished from other gorillas (namely: the mountain gorilla, a subspecies of the eastern gorilla; and the western lowland and Cross River gorillas, subspecies of the western gorilla) by a stocky body, large hands, and a short muzzle.
Males typically weigh between 450 and 550 pounds (204 to 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 tall (1.62 meters), or less.
The lifespan for Grauer’s gorilla is 35 to 50 years in the wild.
Grauer’s gorilla looks a lot like this subspecies’ cousin, the mountain gorilla, with only subtle differences in appearance. A jet-black to blue-black coat covers a slightly narrower physique, and the hair on the head and body is shorter than that of the mountain gorilla. Grauer’s gorilla also has longer limbs, and the nostrils are noticeably rounder than that of the mountain gorilla.
Like all gorillas, Grauer’s gorilla has 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. Ears, hands, feet, are also bare; and in old males, the chest is bare of fur.
And 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 fruit-eaters. Leaves, nuts, seeds, and herbs complement their frugivorous (fruit-based) diet. A fraction of their diet might contain the occasional insect or lizard.
Behavior and Lifestyle
Because Grauer’s gorilla has not been studied in the wild as much as its cousin, the mountain gorilla, less is known about this giant primate’s behavioral proclivities and nuances.
Grauer’s gorillas cover vast distances in search of food, propelling 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. To more effectively gather food, they will create rudimentary tools, using sticks, for example, from their environment.
Morning and afternoons are spent foraging and feeding, with time taken for a midday siesta. Rest breaks include time for grooming one another. At night, the gorillas gather branches and leaves to create a nest in which to sleep. Mothers and babies sleep together.
Grauer’s gorilla is named after Rudolf Grauer, an Austrian explorer and zoologist who first recognized this great ape as its own subspecies.
Grauer’s gorillas live in family groups, known as troops, led by a dominant silverback. Average troop size includes 15 to 20 individuals. Besides the dominant silverback male gorilla, a troop typically includes three unrelated adult female gorillas and four or five young gorillas. Subordinate male gorillas may also be members of a troop.
Upon reaching puberty, at about 15 years of age, 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 become the dominant male, or create a new troop by attracting females who have left an existing troop.
Females, who reach puberty earlier than males, at about 9 years of age, may leave their natal group at that time if the troop’s dominant silverback has died. But they do not always leave. More often, a multi-female group and their offspring will remain intact until a new dominant silverback finds them and assumes the role as their leader and protector. Wildlife biologists speculate that “safety in numbers” keeps the females and their offspring together; they are less likely to be attacked by a leopard or crocodile, their only natural predators, if they remain situated.
Once a silverback has secured his place as the head of the troop, he typically remains with that troop for life, unless forced out by another male gorilla vying for the role as leader. 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.
As characterized by their well-developed social structure, troop members live closely with one another, interact, and travel together. Because of their enormous weight, they spend most of their time on the ground, rather than in trees. Should they decide to climb a tree, however, fully grown adults will keep to a tree’s thick trunk and large branches. Juveniles, who are lighter and more agile, are more likely to climb trees.
As with all gorilla species, vocal communication among Grauer’s gorillas is important. Infants typically emit whines and whimpers; chuckles or laughs accompany play; grunts and whimpers accompany copulation (mating); coughing grunts are used to call attention to a mild threat; “dog whines” indicate a more imminent threat. Screams often indicate alarm. Barks and hoots, used during threat displays, are often accompanied by chest-beating–particularly by silverbacks.
In all, 25 vocalizations—single syllable and multi-syllable and each with its own specific meaning—have been observed in gorillas.
Captive Grauer’s gorillas have been taught to use sign language.
Like their human primate relatives, who ironically are the species’ biggest threat, Grauer’s gorillas (like other great apes) exhibit behavior and emotions similar to the human experience, including laughter and sadness.
Only the dominant silverback is permitted to mate with the females in his troop. By establishing this exclusive bond with each female, the likeliness that members of his harem will leave the troop or mate with another male gorilla is diminished.
Breeding season is throughout the year. Adult females give birth to a single infant about every 4 years, after a gestation period of 8.5 to 9.5 months. Infant mortality is high among these helpless babies, who weigh only 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 squelching any aggression or disputes from younger males 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 able to walk. They are considered weaned at 2.5 to 3 years of age, at which time they become independent of their mothers.
As with other primates who have a frugivorous diet, Grauer’s gorillas are important seed dispersers, playing a critical role in forest regeneration in their fragile ecosystem. Since they travel distances, they disperse seeds far from the mother tree, adding to the diversity of the forest flora.
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 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. If this downward trajectory continues, the species may become extinct in five years.
Although 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 today is illegal hunting for the bushmeat trade. 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.
Grauer’s gorilla joins the western lowland and Cross River gorillas, bearing the ignoble distinction as Critically Endangered. The mountain gorilla is Endangered. All gorilla species may forever disappear from the earth.
International trade of 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.
Congolese wildlife officials from the Institut Congolais pour la Conservation de la Nature (ICCN) oversee the protection of a population that resides in two national parks. However, the majority of Grauer’s gorilla population lives outside of these protected areas.
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 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 committed to saving Grauer’s gorilla from extinction include the Wildlife Conservation Society (WCS), Fauna and Flora International (FFI), the World Wildlife Fund (WWF), and other conservation partners. Some of the initiatives called for by these partners include the immediate creation of the Itombwe Reserve and Punia Gorilla Reserve, which together would conserve over 50 percent of the remaining gorillas; the reduction of poaching and human encroachment; the development of a management plan to ensure the species survival in unprotected areas; and the eradication of illegal mining camps.
Written by Kathleen Downey, September 2016