Grauer’s Gorilla

Grauer’s Gorillas (also known as Eastern lowland gorillas) is a subspecies of the Eastern gorilla. These great apes are only found in the Eastern part of Congo and the IUCN in September 2016 added it on the list of the Critically Endangered Animals in the world. The scientific name of the Grauer’s gorillas is the gorilla beringei graueri.


These gorillas are only found in the eastern part of democratic republic of Congo.

This subspecies is the largest of all subspecies of gorillas, longer arms than the mountain gorillas but have less hair/fur on their bodies than mountain gorillas. They have a population of less than 3000 gorillas. They are critically endangered as they are said to be the most declining gorillas in population. This is due to loss of habitats which are destroyed by man for settlement and agriculture, diseases are also affecting them.

Eastern Lowland Gorillas (Gorilla beringei graueri) have been, and still are, severely affected by human activity, particularly since the 1990s when instability in their area of distribution escalated into civil war, and violence, human tragedy and economic disintegration overshadowed gorilla conservation. Law enforcement is usually one of the first casualties of war. Gorillas are hunted more than ever before in war-torn eastern Democratic Republic of Congo (DRC), and their habitat is rapidly being destroyed and degraded by mining, agriculture and charcoal production.

Anecdotal evidence backed by limited data suggests a significant population reduction over the past 20-30 years and it is assumed that this reduction will continue for the next 30-40 years. The causes of the reduction, although largely understood, have certainly not ceased and are not easily reversible, taking into account the rapidly increasing human population density and the high degree of political instability in the region (IUCN Redlist, 2008. Robbins, M. & Williamson, L.).

Long-term strategy often has to be sacrificed in favor of day-to-day survival. 91% of the human population in the region practice subsistence farming, which requires them to convert the forest into agricultural land. Over 96% of these people rely on firewood, often harvested unsustainably, as their main energy supply for warmth and cooking. Forested parks are for many of them the last remaining source of fuel.

In the last decade, it is believed that the total population of Eastern Lowland Gorillas has declined dramatically, as the lowland populations have been progressively fragmented and reduced (Hart and Liengola 2005; Hart et al. 2007), and conservation efforts hampered or rendered useless by civil war. Their habitat continues to become more fragmented. The corridor linking the lowlands of Kahuzi-Biega National Park with the mountain sector has been illegally cut. Illegal miners, largely dependent on bushmeat for protein, have also entered the forest in search of valuable minerals such as gold, diamonds, tin and coltan, a mineral used in the production of cell phones, computers etc.

Origin of the species name

The American physician and missionary Thomas Staughton Savage first described gorillas (he called them Troglodytes gorilla) in 1847. The name was derived from a Greek translation of the word Gorillai (“tribe of hairy women”), described by Hanno the Navigator, a Carthaginian explorer who led a voyage (circa 480 BC) around the coast of West Africa. There is much academic debate over whether the ‘hairy women’ he saw are what we know as gorillas today.

Scientific name

Gorilla beringei graueri (Matschie, 1914)
In 1914, Paul Matschie, a mammalian taxonomist working at the Humboldt University Zoological Museum in Berlin described as a new species the gorillas inhabiting the lowlands of eastern Belgian Congo. Colin Groves in 1970 revised gorilla taxonomy and recognized Gorilla gorilla graueri, the lowland population of Eastern Gorilla as a subspecies different to the mountain gorilla.

Common names

English – Eastern Lowland Gorilla, Grauer’s Gorilla
French – Gorille de plaine de l’Est, Gorille de Grauer
German – Grauer-Gorilla
Spanish – Gorila de Grauer


The Eastern Gorilla tends to be larger than the Western. Differences between the two species include: longer, blacker hair for the Eastern; the head hair tends not to have red-chestnut tones as is usually the case with adult Western males; Eastern has a more developed sagittal crest along the midline of the skull, indicative of a more powerful jaw musculature; the saddle of silver hair tends to stand out more clearly against the darker hair and to be clearly delineated.

There are few if any absolute physical differences between the two recognized subspecies of Eastern Gorilla. The Mountain Gorilla tends to have very black and longer hair making it densely furred, with a broad face (larger cranium and wider facial skeleton), hairy brow-ridge, massive jaws as well as less rounded and more angular nostrils. Mitochondrial DNA comparisons confirm genetic divergence of the two eastern subspecies, and it is estimated that the two species diverged some 400,000 years ago (Vigilant & Bradley, 2004).

General Biology

Gorillas are mainly terrestrial. The gorilla’s large size and folivorous habits mean that the animals must spend long hours feeding everyday to maintain their body weight. Of all the great apes, the gorilla shows the most stable grouping patterns. The same adult individuals travel together for months and usually years at a time. It is because gorillas eat mainly foliage that they can afford to live in these relatively permanent groups. Foliage, unlike patchy fruit sources generally and especially the ripe fruits that the ape gut requires, is widespread and abundant. In the East, fruit forms a far lower proportion of the gorilla’s diet than in West Africa. Correlated to that, in the Eastern gorilla groups tend to be larger and split into temporary subgroups less frequently than in West Africa, where animals range far apart searching for the relatively scarce ripe fruit.

The Gorilla is a forest species. The Eastern Lowland Gorilla has the widest altitudinal range of any of the gorilla subspecies, living in montane, transitional, and lowland tropical forests. One of the best-studied populations occupies the highlands of Kahuzi-Biega. Here habitats vary from dense primary forest intermixed with bamboo stands, to moderately moist woodland, to areas of Cyperus swamp and peat bog, with alpine and subalpine grassland at higher altitudes.

The varied diet of the Eastern Lowland Gorilla includes a wide range of plants, fruits, seeds, leaves, stems and barks as well as ants, termites and other insects. Seasonality in diet and habitat use is greater for Grauer’s gorillas in low altitude forests than for mountain gorillas. Grauer’s gorilla eats more fruit than Bwindi’s mountain gorilla but not as much as western gorillas. When fruit is scarce, Eastern Lowland Gorillas travel less and increase their consumption of herbaceous vegetation. They also occasionally feed on ants, but insects are never more than a minor part of the diet.

Less is known about the social behavior, feeding ecology, life history and demography of Eastern Lowland Gorillas, compared with the extensive data gathered on the Mountain Gorilla. As far as group structure is concerned, gorillas form harems. It was once thought that gorilla groups contained only one adult male, but around one third of groups in East Africa have been found to host two full-grown males. Adult females in any one silverback’s harem are mostly unrelated, and the social ties that exist between them are weak.

In contrast to many other primates, it is the bond between each individual female and the silverback, rather than bonds between the females that hold the group together. Upon reaching maturity, most males and females leave the group in which they were born. The females usually join another group or a lone young adult male, whereas the males remain solitary until they can attract females and establish their own groups (Yamagiwa, 2003). Both natal dispersal and secondary dispersal (subsequent transfer to yet another group) occur among female eastern gorillas. The structure and group cohesion seems to serve mainly to avoid predators (Yamagiwa & Kahekwa, 2001).

Distribution (current and historical)

The Eastern Lowland Gorilla occurs only in eastern DRC, between the Lualaba river and the Burundi-Rwanda-Uganda border. Its distribution is limited to an area of about 90,000 km², within which it is thought to occupy an estimated 21,600 km² in five regions:

– Kahuzi-Biega National Park and the adjacent Kasese region;
– Maïko National Park and adjacent forest
– Itombwe Forest
– Tayna
– North Kivu Mbohe

The Kahuzi-Biega NP covers an area of 6,000 km², ranging in altitude from 600 to 3,400m. The Park is divided in two parts, a montane sector (ca 600 km²) and a lowland sector (5,400 km²), connected by a recently fragmented forested corridor. Maïko National Park and nearby forests are located in the upland region between the central Congo basin and the mountain ranges of the west side of the Rift. The Park has an area of about 10,800 km² and ranges in altitude from 700 to 1,300m.

There are also several community reserves around the area of Maïko, Virunga and Kahuzi-Biega National Parks which host between 700 and 1,400 gorillas. One of these community reserves encompasses the Itombwe Forest –an area of montane, transitional and lowland tropical forest west of Lake Tanganyika. This nucleus covers an area of 11,000 km² in which gorillas are found in four separate sub-populations. Gorillas also occur in Tayna/Mboke community reserve, and in the Masisi region in North Kivu.

Evaluation and evolution of populations

Eastern Lowland Gorillas have probably been isolated from Mountain Gorillas for 400,000 years and it is estimated that the two eastern taxa separated from their western counterparts at least 2,000,000 years ago.

In the mid-1990s there were estimated to be 17,000 (9,000-25,000) Eastern Lowland Gorillas in at least 11 subpopulations, with about 86% living in the Kahuzi-Biega NP and the adjacent Kasese region of DRC. Recent events in Kahuzi-Biega and the surrounding region, however, indicate that the taxon has undergone a substantial decline in numbers. The available information is very limited, but there is consensus among field workers that a drastic decline in total population has occurred. This is attributed to the combined effects of the rise in demand for coltan ore and the warfare that engulfed the whole of the Eastern Lowland Gorilla range from the late 1990s onwards; armies, rebels, refugees and miners all lived off the land and consumed bushmeat (Redmond, 2001).

The conflict has prevented field surveys in the lowland sector of Kahuzi-Biega, but it is hoped that future surveys will provide an estimate of remaining numbers. The Eastern Lowland Gorilla (G. b. graueri) is listed as ‘Endangered’ on the IUCN Red List (IUCN 2008, EN A4a -d) although if the feared declines are verified, this taxon would be ‘Critically Endangered’.

Ranging behavior

The ranging behavior of gorilla groups is mainly determined by the distribution and abundance of fruit and herbaceous vegetation in the environment (Robbins & McNeilage 2003), which are intrinsically seasonal phenomena. Ranging behavior may also be influenced by social factors such as competition for mates or the mate guarding tactics of silverbacks (Watts, 1994). Eastern Lowland Gorilla groups in the highlands of Kahuzi-Biega NP) have home ranges of 13-17 km² (Yamagiwa et al. 2003). Although the size of their home range in the lowlands is unknown they are likely to be larger.

Conservation Status

The Eastern Lowland Gorilla is a strict DRC endemic. Although no firm figures are available, the Eastern Lowland Gorilla has quite surely been badly affected towards the end of the 20th century. Due to war and conflict, large areas of forest previously occupied by gorillas were cleared and the high demand of fuel wood and food led to human incursions into protected areas. The high price of coltan (columbium and tantalum) ore led to a further invasion (~10,000 people) of Kahuzi-Biega NP – the single most important site for Eastern Lowland Gorillas.

Eastern Lowland Gorillas live in close proximity to (and are sometimes surrounded by) some of the densest rural human populations in Africa, with up to 300-600 people per km² and a correspondingly high demand for land and food. The increasing human population and the corresponding need for land is a serious and ongoing pressure (Hall et al., 1998a). The small isolated Masisi and Mount Tshiaberimu populations are particularly vulnerable to extensive encroachment. The relative remoteness of prime timber areas and the country’s poor transportation infrastructure mean that until now, only low-volume, selective logging has been profitable. Should DRC become more stable, it is likely that commercial logging companies will quickly move into its forests.

Direct exploitation

Hunting has historically threatened the survival of gorillas. Gorillas are hunted for their meat, for body parts for traditional African medicine/magic, as live specimens (particularly infants) for collections, and as trophies. The hunting of gorillas for sale as trophies (skins, heads, skulls, feet and hands) emerged in the mid-1970s, and continued until quite recently. The abduction of infants generally involves the loss of at least one adult, as members of a group will fight to the death to protect their young.

Various armed groups active in DRC are systematically exploiting natural resources to finance themselves. The most important resources are diamonds, copper, cobalt, gold, tin and coltan. The high values of cobalt, coltan, tin and gold have attracted miners to locations in eastern DRC where these minerals are abundant, including streams in Kahuzi-Biega NP. Professional hunters joined the miners to provide meat for them, and the Eastern Lowland Gorillas of Kahuzi-Biega have been severely affected. Traditionally, gorillas were rarely eaten in the eastern Congo Basin, which has given eastern gorillas a certain degree of protection. These traditions are weakest in areas inhabited by the Eastern Lowland Gorilla and, as seen in KBNP, are becoming a thing of the past.

Impact of Conflict

The early 1990s saw the outbreak of fighting in Rwanda, which by April 1994 resulted in a stream of refugees pouring into gorilla habitat in DRC. 860,000 refugees were concentrated in the vicinity of Virunga National Park (Dudley et al., 2002) and a further 332,000 fled into DRC near Kahuzi-Biega. Shortly after the influx of Rwandan refugees came the 1996 war between the armed forces of DRC and a rebel movement backed by Angola, Rwanda and Uganda. Fighting again broke out in 1998 between Rwandan and Ugandan troops and the DRC army.

The streams of refugees that were displaced during these conflicts led to uncontrolled firewood harvesting, and increased poaching. Hunting for gorilla meat in Kahuzi-Biega has increased greatly as a result of war and displacement (Plumptre et al., 2003; Redmond, 2001). In addition to the influx of refugees, the forests that are home to gorillas have served as hiding places and retreats for rebel forces leading to disturbance and hunting. The lowland areas remain largely inaccessible to researchers, but over just 4 years, the highland sector of Kahuzi-Biega NP lost more than 95% of its elephant population and an estimated 50% of its gorilla population.

Conflict has also deterred international conservation organizations, aid agencies and governments from investing in affected areas, leading to frozen budgets, withdrawal of staff, reduction in anti-poaching efforts and closure of projects. Protection of the gorillas in many areas has proved extremely difficult and often hazardous in wartime. In all 92 Congolese park staff are reported to have been killed between 1996 and 2004 (IGCP, 2004; Inogwabini et al., 2000; Iyomi & Schuler, 2002; Iyomi & Schuler, 2003).


Another potential threat to gorillas is exposure to human diseases (e.g Graczyk et al., 2001; Graczyk et al., 2003; Mudakikwa, 2001) particularly for habituated gorillas that come into contact with humans, in areas of gorilla tourism (Homsy, 1999). At present, this threat is a limited one for the Eastern Lowland Gorilla. Strict rules must be observed to regulate viewing duration and extent as well as size of tourist groups. Beside severe impacts on human populations, several outbreaks of the Ebola virus since 2000 might have claimed the lives of thousands of great apes in Africa. Ebola hemorrhagic fever is a severe, often fatal disease that affects humans, gorillas and chimpanzees. Many scientists believe the disease is spread through the butchering and handling of primate bushmeat. So far, Ebola has not affected Eastern Lowland Gorillas.

Other threats

International trade in live gorillas and gorilla parts, which used to be a major threat, has declined since the gorilla was listed in Appendix I of CITES. Accidental entrapment in wire snares used to trap other wild animals is a threat to gorillas. The impact of this threat needs to be assessed in the Eastern Lowland Gorilla area. Occasionally individuals that raid crops are killed.

Regulatory Provisions

CMS: Registered in the Annex I of the CMS since 2005.
CITES: Gorilla is on the Annex I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in 1975.
ACCNNR: The Gorilla is also enumerated in A class of the African Convention for the Conservation of Nature and Natural Resources in 1969.

National laws for the control of hunting and catching exist, but lack of funds, inaccessibility and instability has made application of that legislation difficult. DRC is party of the Convention on Migratory Species, the Convention on Biological Diversity, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the UN Convention to Combat Desertification, the African Convention on the Conservation of Nature and Natural Resources, and the World Heritage Convention.

There are five World Heritage Sites in DRC: Garamba NP, Kahuzi-Biega NP, Salonga NP, Okapi Faunal Reserve and Virunga NP. All are listed as World Heritage Sites in Danger due to human pressures. DRC also participates in UNESCO’s Man and Biosphere (MAB) Programme. The Ministry of Environment, Nature Conservation and Tourism is the government body responsible for nature conservation, although ICCN (the Congolese Institute for Nature Conservation), the National Parks authority, now reports directly to the Office of the President.

Conservation Measures

The taxon is legally protected in its only range state. Great efforts must be made to enforce laws concerning gorillas, including not only effective anti-poaching, but also follow-up of the legal process through arrest and prosecution. The creation of a network of protected areas may ensure security of movement of gorillas in the medium term. Conservation efforts should concentrate on the lowland sector of Kahuzi Biega and Kasese. The restoration and maintenance of a forest corridor between the two sectors of Kahuzi-Biega NP is considered to be essential. The Itombwe forest has also been recommended for particular attention for the conservation of Eastern Lowland Gorillas.