The eastern lowland gorilla (Gorilla beringei graueri), also called Grauer's gorilla, is a type of eastern gorilla that is very endangered. It is found only in the mountain forests of eastern Democratic Republic of the Congo. Large groups of these gorillas live in Kahuzi-Biega and Maiko National Parks, nearby forests, the Tayna Gorilla Reserve, the Usala forest, and the Itombwe Massif.
This gorilla is the largest of the four gorilla types. It has a very dark black coat, similar to the mountain gorilla (Gorilla beringei beringei), but its hair is shorter on the head and body. As male gorillas grow older, their fur turns gray on the back, which is why they are called "silverbacks."
There are far fewer eastern lowland gorillas than western lowland gorillas. A report from 2004 estimated about 5,000 eastern lowland gorillas lived in the wild, but by 2016, this number had dropped to fewer than 3,800. In contrast, there are over 100,000 western lowland gorillas. However, a survey in 2021 suggested the number of eastern lowland gorillas might be as high as 6,800, showing the decline may not be as severe as earlier believed. Despite this, these gorillas still face serious threats. Outside their natural habitat, only one female eastern lowland gorilla lives in captivity at the Antwerp Zoo in Belgium.
Physical description
Eastern lowland gorillas are the largest type of gorilla and the biggest living primates. Male gorillas weigh between 150 and 209 kilograms (331 and 461 pounds), based on measurements from four males. Female gorillas weigh between 73 and 80 kilograms (161 and 176 pounds), though this data comes from a small number of females. Male gorillas are between 1.69 and 1.96 meters (5 feet 7 inches to 6 feet 5 inches) tall, while females are about 1.6 meters (5.2 feet) tall. A different study of eight wild adult males found their average weight to be 169 kilograms (373 pounds).
Habitat and ecology
Gorillas spend many hours each day eating plants. They live in groups for months or years, similar to how a family functions. Groups of eastern lowland gorillas are often larger than groups of western gorillas.
The eastern lowland gorilla lives in the widest range of heights among all gorilla types. They are found in mountainous areas, areas between mountains and lowlands, and in lowland tropical forests. One well-known group of eastern lowland gorillas lives in the Kahuzi-Biega highlands. Their habitats include thick forests, moderately moist woodlands, Cyperus swamps, and peat bogs.
Gorillas do not eat banana fruits, but they may damage banana trees to eat the soft, nutritious part inside the trunk. Eastern lowland gorillas prefer areas where plants are growing again, such as places near old villages or farmland. Farmers who have seen gorillas in their fields sometimes kill them to protect their crops and sell the meat in markets.
Eastern lowland gorillas eat a variety of plants, including fruits, leaves, stems, and bark. They also eat small insects like ants and termites, but insects make up only a small part of their diet. Compared to western lowland gorillas, which live in low-altitude tropical forests, eastern lowland gorillas move less and eat more plants with soft stems.
Behaviour
Eastern lowland gorillas are very friendly and peaceful, living in groups of two to more than 30. A group usually includes one silverback, several females, and their young. Silverbacks are strong, and each group has one dominant male, called an alpha male. These males protect their group from danger. Young silverback males leave their birth group when they become adults and then try to attract females to create their own groups.
Not much is known about the social behavior, history, or environment of eastern lowland gorillas, partly because of the civil war in the Democratic Republic of the Congo. However, some social behaviors have been studied. For example, gorillas form groups that may include two adult males. One-third of gorilla groups in East Africa have two adult males in their group.
Most primates are connected through relationships between females, a pattern also seen in many human families. Once they reach adulthood, both males and females usually leave their group. Females often join another group or a lone adult male silverback, while males may stay together for a time until they attract females and create their own groups. It is commonly believed that the structure of gorilla groups helps protect them from predators.
A female gorilla gives birth to one baby after a gestation period of about 8 and a half months. She breastfeeds for about three years. The baby can crawl at around nine weeks old and can walk at about 35 weeks old. Infant gorillas stay with their mother for three to four years and reach maturity at about 8 years old (females) and 12 years old (males).
Threats
Threats to the survival of the eastern lowland gorilla include poaching, civil unrest, and the destruction of their habitat due to logging, mining, and agriculture.
The main reason for the decrease in the number of eastern lowland gorillas is poaching for bushmeat, which is meat hunted for food. Displaced people, militia groups, and loggers or miners in the area eat this meat. Studies have found that great apes, such as chimpanzees and bonobos, make up 0.5–2% of the meat sold in bushmeat markets. Some research suggests that about 5 million tonnes of bushmeat are traded each year. This hunting harms gorilla populations because they reproduce slowly and their numbers are already low. Even though gorilla meat makes up a small part of bushmeat sales, it still causes their numbers to drop. Endangered Species International reported that about 300 gorillas are killed each year to supply bushmeat markets in the Congo.
Civil unrest in the Democratic Republic of the Congo has led to fewer eastern lowland gorillas. The area where these gorillas live has decreased from 21,000 to 12,000 square kilometers over the past 50 years. This species now occupies only 13% of the area it once lived in. Violence in the region has made research difficult, but scientists estimate that their population has dropped by more than 50% since the mid-1990s. In the mid-1990s, their population was close to 17,000.
The civil war in the Democratic Republic of the Congo has caused military groups to stay in forests for long periods, increasing poaching as militia and refugees face hunger. Military leaders have also removed weapons from park guards, leaving them unable to control activities in national parks or stop people entering them when faced with armed soldiers. Militia groups in the region limit efforts to protect the eastern lowland gorilla. Studies suggest that more than half of the 240 gorillas known in one study were killed due to poaching. Researchers also note that patrolling areas outside of parks is harder, and poaching may be even worse there.
Conservation groups worked with rebels in the eastern Democratic Republic of the Congo to re-arm park guards. After the war began, the government stopped funding the parks. Conservation groups, such as the International Gorilla Conservation Program and the German development agency, have supported the guards for several years.
Many multinational companies indirectly or directly fund the civil war in the Democratic Republic of the Congo by buying illegal resources from the region or trading resources for weapons. In 2007, reports showed that 14,694 tonnes of cassiterite (worth $45 million), 1,193 tonnes of wolframite ($4.27 million), and 393 tonnes of coltan ($5.42 million) were exported. Coltan, in particular, is a key resource used in cellphones and is in high demand. One company, Traxy's, bought 226 tonnes of coltan in 2007, which was 57% of the Congo’s total coltan exports. The United Nations Environmental Programme reported that resources from companies and pension funds in industrialized countries are used to fund corruption and arms sales, which may involve "conflict" natural resources. Private companies have been found to trade weapons for resources or provide access to weapons through subsidiary companies.
About two million people, directly or indirectly connected to the 1994 Rwandan genocide, fled to Tanzania and the Democratic Republic of the Congo, mainly to Virunga National Park. It is estimated that 720,000 refugees lived in five camps near the park. Deforestation happened as 80,000 refugees entered the park daily to find wood, causing a deforestation rate of 0.1 square kilometers per day. When the Congo war began in 1996, 500,000 refugees remained, increasing pressure on natural resources, including the eastern lowland gorilla.
Illegal logging may occur by companies without land rights or by legal landowners. Over-harvesting, an illegal practice often done by legal concession holders, leads to deforestation and the export of illegal resources. Areas logged are important gorilla habitats and are a global concern. Companies involved in illegal logging contribute to environmental damage and support the illegal resource trade controlled by militia groups.
Conservation
Most parks in the Democratic Republic of the Congo are unsafe areas that make it hard for park rangers to work. Park rangers are trained to stop illegal hunting, but there are not enough rangers, and they do not have the training or tools needed to deal with groups of armed people. In Virunga National Park, for example, 190 park rangers have been killed over the past 15 years because of civil war. Laws that require countries to work together across borders have helped reduce the loss of eastern lowland gorillas. These laws also helped stop the illegal removal of resources from Virunga National Park, which reduced the money that armed groups could use to fund their activities. Although rangers have limited the amount of illegal resources being taken from the area, armed groups have responded by killing gorillas to scare the rangers. On July 22, 2007, 10 gorillas were killed as punishment for the rangers stopping the illegal transport of resources like wood. Armed groups continue to control the region because of support from nearby countries. These groups trade minerals and timber illegally for weapons, and some officials and companies from other countries are involved. Gorillas are also in danger because of hidden traps placed in the forest. While violence from armed groups harms gorillas, the main reason their population is declining is because of damage to their homes caused by the removal of natural resources.
Genetic studies
There was already evidence that inbreeding caused health problems in some gorilla groups, such as birth defects like syndactyly, where fingers or toes are fused together. A recent study of gorilla DNA, which included all four types of gorillas, examined how much genetic variety exists among the remaining gorilla populations and how different they are from one another. The study found that the eastern lowland gorilla group is actually two separate subgroups. This division might be due to the small number of gorillas studied or the way gorillas in this group live together socially. The findings show that the eastern lowland gorilla subgroup has very little genetic variety, which could make it harder for them to survive and adapt to changes in their environment. This lack of variety is likely because the group started with only a few ancestors and had little movement between groups, leading to high levels of inbreeding. Conservation efforts for the eastern lowland gorilla suggest creating breeding programs in captivity or moving individuals between the two subgroups to help increase genetic diversity.