Eastern gorillas are the largest species of gorilla and the world’s largest living primate. They are divided into two subspecies – eastern lowland gorillas (Grauer’s gorilla) and mountain gorillas. These gorillas are closely related to humans and can perform several tasks like a man. The DNA of eastern gorillas is 98% similar to humans.
The heaviest individual recorded was a 589 lb (267 kg) silverback shot in Ambam, Cameroon.
Body and Coloration: Eastern lowland gorillas have a thick layer of deep black fur, while eastern mountain gorillas have bluish fur. Mountain gorillas are smaller and lighter than eastern lowland gorillas. When they are 12, the fur on the male’s back changes from black to grey.
Compared to the rest of their bodies, they have large heads covered with fur – except for their completely bald faces. The face of an eastern gorilla includes ridges above their eyes, a flat nose with enlarged nostrils, small ears, and larger jaws compared to other gorilla species. Their chests are bare and wide. The long arms end in hairless hands and fingers, of which the thumbs are larger than the other digits. Like other gorillas, a strong smell emits from the apocrine glands in their armpits when they are under stress. The arms of the eastern gorilla are about 15% longer than their legs.
Sexual dimorphism exists in this species as males tend to be bigger than females. Also, a male eastern gorilla can be identified by his sharp and large canine teeth.
They have a silvery saddle on their back, which becomes white as the gorilla ages. Because of their silver saddle, older males are often called silverbacks.
Mountain gorillas inhabit the forests of the eastern Democratic Republic of Congo (DRC), southwestern Uganda, and Rwanda. Two subpopulations live in the Virunga mountains at about 1500-4000 meters above sea level and the steep mountains of Bwindi National Park in Uganda at 1100-2400 meters.
Eastern lowland gorillas dwell across the forests of the Albertine Rift in eastern DRC. Their home range is smaller than western gorillas. They are found between the Tanganyika and Edward Lakes and the Lualaba River.
Previously, their home range was 8100 square miles, but now it has decreased to 4600 square miles. These days they occupy only 13% of their historical range.
They reside in mountain rainforests, dense montane forests, subalpine forests, and sometimes in swamplands if the proper vegetation grows. They sleep in nests that are built on treetops.
Eastern gorillas are herbivores, and they follow a foliage-based diet. They also eat fruits if they are available in the area they inhabit. Sometimes they eat flowers, bark, roots, and small invertebrates.
These gorillas are diurnal. They spend 40% of the day resting, 30% on feeding-related tasks, and the remaining 30% traveling. Foraging mostly occurs in the morning and late afternoon. At night, they stay in their nests that are built by folding over vegetation on the ground.
They are semi-terrestrial species that do not always live on land, spending a lot of time on treetops.
Eastern gorillas live in stable, cohesive family groups of up to 35 members. A dominant silverback male is the head of the family and protects the females and the infants.
To defend his family, a male silverback will beat his chest as a warning. If that isn’t enough, he will charge at the perceived threat.
Adult males rule over a single territory, often fighting to gain control over an area or a female.
The gorillas beat their chest to create an emanating drumming sound to attract females and intimidate rival males.
These gorillas are intelligent and communicate with 25 different noises.
The lifespan of these gorillas is between 40 and 50 years.
Eastern gorillas have opposable thumbs, which move in a different direction than their other fingers, making it easier to grab different things and gather food.
They have strong, large arm muscles that help to defend themselves against potential threats and gather food.
Just like opposable thumbs, these gorillas also have opposable toes that aid them in climbing trees with ease. Their feet have a tough bottom which makes it easier for them to walk on rocks and grass.
Mating and Reproduction
These gorillas are polygynous, where one dominant male of the group can mate with all the females of that group. They form groups called harems with one male and several females. Grooming occurs between males and females or between females.
Breeding takes place throughout the year. While mating, the female first approaches the male slowly and hesitantly. After giving birth, the females cease to ovulate for several years and only reproduce once every 3-4 years.
Their gestation period is 8.5 months, after which the mother gives birth to a single baby gorilla with a greyish-pink skin color. The mother carries the baby until it is nine weeks old, after which it can start crawling. After 30–40 weeks, it learns to walk.
Female gorillas reach reproductive maturity at 10, while males reach maturity at 15. The mother breastfeeds the baby for a year, but weaning occurs when it is three and a half years old.
Large animals like leopards and the odd crocodile are the primary predators of eastern gorillas.
These species are put on the list of “Critically Endangered” or “CR” species by the IUCN. In the last 20 years, their population decreased by 70%, with current estimates putting the number of gorillas in the wild at about 6000 or less.
The reason behind this decline is due to habitat destruction (for commercial, agricultural, and residential purposes), habitat fragmentation (by transportation corridors and resource extraction procedures like mining), and diseases. The population of mountain gorillas is under less threat than the lowland gorillas, and their numbers have been on the rise.
Conservation efforts for eastern gorillas include protecting them in parks and zoos, however the only zoo where eastern gorillas are currently housed outside their range is the Antwerp Zoo in Belgium. However, exposure to humans from these parks has led to the gorillas being infected by zoonotic diseases like scabies. Another way to preserve them is by regulating tourism, minimizing contact with humans, and preventing them from contracting diseases.
Genetic studies are also conducted to identify the levels of diversity and divergence among the remaining population of the eastern gorilla. Conservation interventions have suggested captive breeding programs or translocations between the eastern lowland subgroups to lower the rate of inbreeding.
However, the biggest hurdle to conserving these species has been the civil unrest faced in the places where they live, most notably the Democratic Republic of Congo (DRC).
Eastern gorillas are afraid of water and do not like getting wet. They try to avoid streams and rain.
The punch of a gorilla is strong enough to scatter the skull of a human. They can punch with a force of 1300 to 2700 pounds.
It is advisable to avoid eye contact with a gorilla as it considers anyone who keeps direct eye contact with them a challenger and an enemy. Direct eye contact can provoke the gorilla to attack you.
Eastern gorillas are larger and have darker and longer fur than western gorillas.
Just as humans have unique fingerprints, these gorillas have distinct nose prints.