Mountain Gorilla, Gorilla beringei beringei
MOUNTAIN GORILLA
Gorilla beringei beringei
Geographic Distribution and Habitat
Mountain gorillas are endemic to a small region in Central Africa, known as the Virunga Massif, which spans the countries of Rwanda, Uganda, and the Democratic Republic of Congo (DRC). The entire population of these large apes is restricted to a range of about 300 square miles (777 sq. km), which is only about the size of New York City!
They live in high-elevation montane forests (as high as 14,764 feet (4500 m)) where fruiting trees are scarce. The population is split across two sub-populations that live in two montane forest regions, Virunga Massif and Bwindi-Sarambwe, that are separated by human-cultivated regions. Mountain gorilla habitat is characterized by dense ground cover vegetation, including woody shrubs, bamboos, and subalpine forests, which typically have spreading canopies.
Mountain gorillas are well studied, and many populations have been habituated to researchers and tourists. One of the most popular research facilities studying the species is the Karisoke Research Center of the Dian Fossey Gorilla Fund International.
There are two subpopulations of mountain gorillas, located in the Virunga Massif and the Bwindi-Sarambwe regions. These two habitats are separated by approximately 18.7 miles (30 km). Early explorers and naturalists observed minor differences in size, fur length, and build between gorillas from these regions, and mistakenly classified them as separate species. Today, we recognize these variations as normal differences within a single species or subspecies, not indicators of distinct taxonomic groups.
The species name beringei comes from Robert von Beringe, a German army officer who shot and collected the first two known specimens of mountain gorillas in 1902. The mountain gorilla (Gorilla beringei beringei) was initially classified as a subspecies of the western gorilla (Gorilla gorilla). In 2001, scientists revised the species’ taxonomic classification and nomenclature to recognize it as one of the two subspecies of the eastern gorilla (Gorilla beringei). The other subspecies is the Grauer’s Gorilla (Gorilla beringei graueri)
Size, Weight, and Lifespan
Mountain gorillas are larger than the other eastern gorilla subspecies. Although both male and female mountain gorillas are approximately the same height of 5.6 feet (170 cm), males have significantly heavier and more muscular builds. Males typically weigh 358 pounds (162.5 kg) on average, while females are approximately half that weight at 215 pounds (97.5 kg).
Mountain gorillas have a significantly longer lifespan compared to other primate species, with males typically living up to 39 years and females around 44 years.
Appearance
Mountain gorillas can be distinguished from other gorilla species by their long, coarse, dark black or blue-black hair, which often hangs over their faces. Their thick hair is an adaptation to the colder climates of their high-elevation homes in the montane forests, where temperatures can drop below 32 degrees Fahrenheit (0 degrees C).
As males mature, the hair on their upper back turns a silvery grey, and these individuals are commonly referred to as “silverbacks.” In contrast, adolescent males are referred to as “blackbacks.” In gorilla troops, the dominant male leader is often the oldest and largest male, and he can be easily distinguished by his clearly defined silver-grey “saddle” coloration. A troop can have multiple mature male silverbacks, but only one silverback will take on the dominant role of leader of the troop.
They have the typical features of great apes—forward-facing eyes, dry noses with nostrils that point downwards, opposable thumbs, and flat nails on their fingers and toes. The wrinkles above their noses form patterns distinct enough that researchers have used them to identify individuals from photographs. These “noseprints” are a valuable tool for distinguishing individuals, tracking their behavior, and monitoring them in large populations where individuals can appear similar.
Mountain gorillas are sexually dimorphic, meaning that males and females exhibit noticeable differences in appearance. The most significant difference is size; adult males are almost twice as heavy and much more muscular than females. Males also have other distinct features called secondary sexual characteristics. These include large bony eye-sockets (supraorbital ridges), a powerful crest on top of the skull where strong jaw muscles attach, a thick hump on the back of the neck (nuchal crest), enlarged jaws, and large canines.
Diet
Mountain gorillas are primarily herbivores, feeding on a variety of plants, including leafy vegetation, woody plants, and roots. They also eat insects, such as ants and bees, along with earthworms and dirt, to obtain essential nutrients. Because the high-altitude forests where they live don’t produce much fruit, mountain gorillas rely heavily on protein-rich plants to keep their energy up.
To maintain their massive size, they spend much of the day eating, sometimes as much as 40 pounds (18 kg) of plants in a single day. Since the plants they eat contain a lot of moisture, mountain gorillas rarely need to drink water. They get most of their hydration directly from their food.
Mountain gorillas have large, protruding bellies because their digestive systems are built to handle massive amounts of bulky plant material. They have large, simple stomachs that aren’t divided into chambers like those of some other herbivores. Plant material is first digested with acid in the stomach, then moves to the intestines, where bacteria help break down the fiber through fermentation. Their long intestines allow extra time to break down this fibrous diet and extract as many nutrients as possible.
Leaves and bark are packed with tannins, the same chemical that gives tea its dark color and bitter taste. Since gorillas eat so much of this tannin-rich vegetation, their teeth often become stained black over time.
Behavior and Lifestyle
Mountain gorillas are diurnal, spending the early mornings and late afternoons foraging for the large amounts of food they need. Families rest together and build nests on the ground using nearby leaves and shrubs. They often make separate nests for daytime and nighttime rests, reusing the same spots, but rebuilding the nests each time.
Mothers share nests with their infants, but by the age of four, young gorillas begin building their own. Large silverbacks put considerable effort into their nests, which can reach over 5 feet (1.5 meters) in diameter.
They are primarily terrestrial (ground-dwelling) and quadrupedal, walking on all fours. Their primary mode of movement is knuckle-walking, where they bear the weight of their upper body on their knuckles. Knuckle-walking is a crucial adaptation that enables them to balance their heavy bellies and powerful hindquarters, and the strength required for it develops gradually over time.
Gorilla infants are first carried in their mother’s arms, and as they grow older, they are carried on her back. At around four months old, they experiment with bipedal walking. At this stage, young gorillas have relatively stronger arms compared to their legs, which is why they’re often seen climbing and playing in trees. As they grow, they become too heavy to remain arboreal (living in trees) and shift to moving on all fours, placing their full palms on the ground initially. This posture helps support their growing bellies and developing leg muscles. Between 17 and 21 months of age, young gorillas transition fully to knuckle-walking, mimicking the adult style of movement. By the time they’re about two years old, the balance of strength in their limbs shifts. Their legs become much larger and stronger than their arms, better suited to supporting their size and lifestyle on the forest floor.
They may appear slow, but mountain gorillas can sprint surprisingly fast over short distances, reaching speeds of 23 to 25 miles per hour (about 40 km/h).
Tool use in mountain gorillas is less commonly documented compared to other great apes. There have been a few observed cases, such as using sticks to probe for ants or, in one instance, a mother using a bamboo stick as a ladder to help her young climb up to her. These behaviors show that mountain gorillas are capable of observing their environment and finding solutions to problems. However, they likely do not need to use tools as often as other species because their primary food source, plants, is abundant and readily accessible.
Grooming in mountain gorillas is mainly seen between mothers and their infants, or between individuals with close social bonds. The primary purpose is hygiene, removing pests like insects or ticks, which also provides a convenient snack for the groomer. In many primates, grooming plays a crucial role in maintaining social relationships; however, in mountain gorillas, it appears to be less central to social bonding. Instead, their social closeness is more often maintained through “proximity patterns,” where individuals regularly sit or rest near each other while feeding or relaxing.
Homosexual behaviors, meaning sexual interactions between individuals of the same sex, have been documented in both male and female mountain gorillas. In males, this behavior is often observed in all-male groups or among juveniles, who exhibit curiosity. In females, researchers believe it may be linked to elevated reproductive hormones and sexual gratification.
Mountain gorilla populations are increasing, which is a positive sign for conservation efforts.
Adult male gorillas are called “silverbacks” due to the distinctive silver hair that develops on their backs.
Juvenile males are known as “blackbacks” until they mature.
Mountain gorillas can eat up to 40 pounds of vegetation in a single day.
Their teeth often turn black because of the high tannin content in their diet.
They are vulnerable to human illnesses, so keeping a safe distance is important for their health.
Infant gorillas have stronger arms than legs, but this balance shifts as they mature into juveniles.
Mountain gorillas usually wake at around 6 a.m.; however, on cold, misty mornings, they may stay in their nests a bit longer. Their day is mainly spent foraging and eating to obtain enough nutrition to maintain their energy levels. They do not travel far, usually covering between 0.5 and 0.6 miles (about 0.05 to 1 km) each day as they move through the dense mountain forests of Central Africa.
As they travel, they stop at food patches and eat as much as they can until the hot midday hours, when they rest. During this break, they build temporary nests to relax, play, groom, or bond with each other. This resting and social time is an important part of their daily routine and helps strengthen social bonds.
After their midday break, they forage again until just before sunset. Then they build new nests for sleeping. On average, mountain gorillas spend about 45% of their active time feeding, 6.5% traveling, and 3.5% socializing.
Mountain gorillas live in troops of an average of 10 individuals, with some groups being larger than 40 gorillas. The core of the family troop is formed between the dominant male, known as the silverback, and his females. A typical troop can consist of multiple females, their offspring, immature blackbacks, and at least one dominant silverback.
Gorillas have a high tolerance for large groups because their food source of plant matter is abundant, and there is little competition among individuals for food. The silverback is the most dominant and usually has the reproductive advantage of mating with the females. Non-dominant males also have a hierarchy, with dominance categories of beta (the next dominant and most likely challenger to the silverback) and gamma (the subordinates).
Male and female relationships are the strongest social bonds within a gorilla troop, with males spending a significant amount of their time with females. Gorillas are not strictly monogamous and do not form lifelong pair bonds. Females often transfer between groups throughout their lives. Within a troop, female hierarchy is relatively loose, with older females typically being the most dominant. Competition among females is usually centered on access to food. However, related females sometimes form close, long-term bonds that can last for years and may even encourage some females to stay in the group rather than leave.
Young gorillas spend a lot of time playing with each other. Play helps them explore their environment and learn about the strength and flexibility of their bodies. Playing also helps develop social skills and develop bonds between the young and the adults. Juvenile gorillas often like to be near the dominant silverback, the leader of the group. They will try to sit close to him.
Most mountain gorilla troops have only one silverback male, who is the dominant male within the troop. However, about 40% of troops have multiple silverbacks, with one male being the most dominant among them. The dominant silverback has the most access to mating with females, but subordinate males also sometimes mate when the leader is not paying attention. Researchers have estimated that about 50% of the matings have occurred between subordinate males and females. As a result, most of the infants in a troop are likely the dominant male’s offspring, but some may belong to one or more of the subordinate males.
Gorillas cannot easily identify which infant belongs to which male. This serves as a form of protection. If the dominant silverback is ever replaced, the new leader is less likely to commit infanticide (killing the previous male’s offspring) because he won’t know for sure which infants are his. This is one reason why dominant silverbacks tolerate other mature males in the group. Having more males can attract new females to join, and it also lowers the risk of the silverback’s offspring being killed if leadership changes. However, sometimes the risks of keeping other males in the group outweigh the benefits. Subordinate males may challenge the dominant silverback, try to take over the group, and steal his females. When this happens, more aggressive behaviors and displays are often seen.
Troops can fission, or break up, mostly when females leave either by themselves or with their offspring. Multi-male groups of multiple silverback bachelor males can also form when there are not enough mature females to join them to be a family troop. In the Virunga volcano region, approximately 10-40% of the groups have been multi-male over the 30 years of research. Silverbacks can also be found as single units and are often referred to as a “lone silverback”. When a troop’s dominant silverback dies, the next dominant silverback will take over.
Gorillas are highly expressive and communicative apes. Researchers have spent a considerable amount of time close to these primates and have been able to break down an impressive number of vocalizations and behavioral displays that they use to communicate with one another.
The most iconic form of gorilla communication is chest drumming—a loud, resonant sound that can carry nearly 0.6 miles (1 km) through the forest. In larger groups that tend to spread out, visibility in the dense vegetation is limited, so loud, high-pitched calls are especially useful for keeping track of one another’s location.
Mountain gorillas are the most vocal of the eastern gorillas, with a wide range of sounds used to communicate everything from group coordination to emotional states. Males are generally more vocal than females, and their calls include at least three types of aggressive sounds, two alarm calls, two distress calls, three gathering calls, and one that seems to be used specifically to communicate with other gorilla groups.
Their vocal repertoire includes growls, roars, grunts, panting, barks, cries, whines, hoots, and a sharp “wraag” alarm bark. Long-distance hoots often resemble owl calls, while grunts may be used to guard food or signal others to keep their distance. Roars and screams are linked with aggression or alarm. Interestingly, gorillas also hum or “sing” softly and sway while feeding—especially when enjoying a favorite food.
Aggressive displays are typically intended to demonstrate their size and strength. As the primary protector of the troop, the dominant silverback performs the most displays. These include chest beating, thrashing around, and using leaves and branches to create louder sounds and produce dramatic visual effects, thereby amplifying the display.
You may have noticed the long, sharp canines in gorillas, especially in males. Since they are primarily herbivorous, why do they need such large canine teeth? Male gorillas use their canines as part of threat displays. They open their mouths wide and show their teeth to intimidate rivals and signal aggression. These displays serve as a means to avoid actual fights, which can be dangerous and result in injuries for both the aggressor and the defender. Older, larger males tend to have longer canines, so these displays often help determine who the likely winner of a fight would be, without the need for physical conflict.
When males direct their displays toward females, the females respond with appeasement behaviors. These displays indicate submission and signal acceptance of the dominant male’s authority.
Just like humans, gorillas sweat. They have many glands in their armpits that also secrete scent, which can be used in olfactory (sense of smell) communication. When alarmed, silverbacks can emit a strong odor that alerts other members to the presence of danger nearby. When females are in estrus (hormonally ready to mate), they emit a scent that attracts males.
There is no specific breeding or mating season in mountain gorillas, and the timing of matings may be influenced by food abundance. Females become sexually mature around 8 years of age, while males take longer, reaching sexual maturity between 10 and 12 years. By around age 13, males develop the full secondary sexual characteristics of a silverback. Once they become silverbacks, they are large and dominant enough to gain reproductive rights over females.
Females typically give birth when they are 10 years old and can bear offspring every four years or so. The gestation period (time a female is pregnant) is about 8.5 months. Usually only one offspring is born, though there have been reports of twins. Most infant deaths occur due to infanticide when the dominant silverback dies and an outside male takes over. As a result, infant survival is high in multimale groups.
Mothers develop strong bonds with their offspring, and they remain social with each other even when the young disperse. The silverback rarely takes an active parenting role; however, he often plays with or tolerates young gorillas around him. Juveniles are usually attracted to silverbacks and tend to stay close to them. The bond between mother and child is strong, and sometimes a dead infant will be carried and cared for by their mother. Researchers have documented gorillas returning to the site of a deceased family member.
Newborns weigh approximately four pounds and are entirely dependent on their mothers, as they are too weak to move about or hide, much like human babies. Unlike human babies, gorilla infants develop at twice the rate and start moving away from their mothers by the time they are three months old. Newborn gorillas are fully weaned off their mother’s milk by the age of three years.
Mountain gorillas are considered infants until they are about three and a half years old, when they can survive on solid food alone. From ages 3.5 to 6, they are considered juveniles, and from 6 to 8, they are referred to as subadults. Female gorillas are considered adults after 8 years of age. Males, on the other hand, are known as blackbacks between the ages of 8 and 12. When they develop the silver fur on their back or “saddle,” they are called Silverbacks.
Until females are about ten years old and males are around eight years old, young gorillas appear similar. After that, males begin to grow much faster and eventually become almost twice the size of adult females. Females reach their full size by around 12 years old, while males continue growing until approximately 13 years old.
Both males and females can disperse or leave their natal troop (the troop where they were born). Males can become subordinate in another silverback’s troop or become a lone silverback. Females disperse to a solitary male to create a troop, or they can join an existing troop. After that, females can transfer multiple times between troops and mate with numerous silverbacks throughout their lifetime.
The smallest mountain gorilla family unit would consist of one dominant silverback and a female who will eventually have offspring. However, typical mountain gorilla social groups are often polygamous, meaning individuals have multiple mates. These groups can include one to four silverbacks, around five unrelated adult females, and their offspring.
Mountain gorillas thrive in dense, high-elevation forests where fruiting trees and tall canopies are rare. Without a thick canopy, fast-growing shrubs and grasses, such as bamboo, take over the forest floor. Gorillas consume large amounts of this vegetation, effectively acting as ecological gardeners by dispersing seeds and pruning plants. This helps regulate plant growth and maintain a diverse, healthy plant community.
Mountain gorillas share their habitat with other primates, including golden monkeys (Cercopithecus mitis kandti), guerezas or black-and-white colobus monkeys (Colobus guereza), and eastern chimpanzees (Pan troglodytes schweinfurthii). There is little competition for food between gorillas and these other primates because gorillas mainly eat leaves, stems, and other plant matter. In contrast, the other species focus more on fruit.
Eastern chimpanzees have been observed showing aggression toward gorillas, primarily due to competition for space rather than food. Generally, these species coexist peacefully.
Leopards and potentially hyenas prey on mountain gorillas, primarily targeting infants and juveniles.
The International Union for Conservation of Nature lists the mountain gorilla as Endangered (IUCN, 2018), appearing on the IUCN Red List of Threatened Species.
Recent numbers indicate that the mountain gorilla population has been increasing to the point where their status was downgraded from Critically Endangered to Endangered. Habituated gorillas tend to be detected more easily and skew detection probabilities and counts more than the unhabituated gorillas, which are harder to detect. In other words, gorillas that are used to humans are easier to spot, which can make them seem more common than shy gorillas that are harder to find. This makes identifying and accurately counting them challenging. Researchers know that the mountain gorilla population has increased, but they are actively working on developing more effective methods to determine the exact extent of the increase. Current estimates suggest that the total population is at least 1,004 individuals.
Forest degradation, political instability, and human encroachment are the biggest threats to mountain gorilla conservation. When governments are unstable, conservation efforts often get deprioritized, and people living in poverty are forced to rely on natural resources to sustain their livelihoods. This leads to deforestation for firewood, hunting wildlife for food, and clearing land for farming, all of which shrink the gorillas’ habitat.
Mountain gorillas face risks from snares set for other animals. Even though they are not usually hunted, they sometimes get caught in traps meant for smaller wildlife, which can lead to serious injuries or death. Infants, particularly, are captured by poachers, and they are inadvertently killed in the process, especially in snare traps.
Another major threat to mountain gorillas is disease. Because they are so closely related to humans, they are vulnerable to catching human illnesses, especially respiratory infections, which can be deadly. As humans move closer into gorilla habitats, there is an increased risk of spreading zoonotic diseases (illnesses that jump between species) such as the flu, pneumonia, and Ebola. Gorillas do not have natural immunity to these diseases, making the threat even more serious.
The mountain gorilla is 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.
Mountain gorillas are protected throughout their range by national and international laws that prohibit their killing and trade. Their populations live mainly within protected areas, including Volcanoes National Park in Rwanda, Mgahinga and Bwindi Impenetrable National Parks in Uganda, and Virunga National Park in the Democratic Republic of Congo. A transboundary collaboration that harnesses the political power of these countries has been in place for several years, supporting wildlife habitat protection, eco-tourism, and law enforcement. These countries work closely with non-governmental organizations such as the Dian Fossey Gorilla Fund and the Karisoke Research Center. Together, they engage local communities, support ongoing monitoring and research, and provide vital veterinary care to help ensure the survival of mountain gorillas.
Much of what we know comes from gorilla populations that have been habituated by researchers. Eco-tourism has also helped fund gorilla conservation efforts and provided employment opportunities for local communities. However, eco-tourism companies rely on developing roads and facilities to expand their client capacities to make a profit, and this often leads to the exploitation of gorillas and their habitat. Too much contact with humans can stress gorillas and raise the risk of spreading disease. To protect them for generations to come, we must limit how often people visit and always keep a safe distance. The International Union for Conservation of Nature (IUCN) has outlined its Best Practice Guidelines for Great Ape Tourism to help businesses balance profitability with environmental sustainability.
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Written by Acima Cherian, Jul 2025