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Gorilla beringei

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA PRIMATES HOMINIDAE

Scientific Name: Gorilla beringei
Species Authority: Matschie, 1903
Infra-specific Taxa Assessed:
Common Name(s):
English Eastern Gorilla, Mountain Gorilla
Taxonomic Notes: The eastern species of gorilla (Gorilla beringei) consists of two subspecies, Gorilla beringei beringei (Mountain Gorilla) and Gorilla beringei graueri (Eastern Lowland Gorilla or Grauer’s Gorilla). Gorilla beringei beringei is found in two isolated subpopulations, Bwindi Impenetrable National Park, Uganda, and the Virunga Volcanoes region of Rwanda, Uganda, and Democratic Republic of Congo (DRC). While there has been some debate as to whether Bwindi gorillas should be considered as a separate subspecies (Sarmiento et al. 1996, Stanford 2001, Grubb 2003), they are considered here as one subspecies following Caldecott and Miles (2005) and Groves (2006).

Assessment Information [top]

Red List Category & Criteria: Endangered A4abcd ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Robbins, M. & Williamson, L.
Reviewer(s): Mittermeier, R.A., Butynski, T.M. & Tutin, C. (Primate Red List Authority)
Justification:
Eastern Gorillas have been and are still severely affected by human activity. They are hunted, more now than before in war-torn eastern DRC; and their habitat is being destroyed and degraded by mining and agriculture. They are estimated to have experienced a significant population reduction in the past 20-30 years (one generation is ~ 20 years: Werikhe et al. 1997; Robbins and Robbins 2004) and it is suspected that this reduction will continue for the next 30-40 years. The maximum population reduction over a three-generation (i.e. 60 year) period from the 1970s to 2030 is suspected to exceed 50%, hence qualifying this species for Endangered under criterion A4. The causes of the reduction, although largely understood, have certainly not ceased and are not easily reversible. The suspected future continuation of the population reduction is based on a precautionary approach taking into account the rapidly increasing human population density in the region and the high degree of political instability in the range states.
History:
2000 Endangered

Geographic Range [top]

Range Description: Eastern Gorillas are found in Rwanda, Uganda, and eastern DR Congo. There are two subspecies.

G. b. beringei (Matschie, 1903) is found in the Virunga Volcanoes region, an area of 440 km² straddling the border between Uganda (Mgahinga Gorilla National Park), Rwanda (Volcanoes National Park), and DRC (Virunga National Park), and also in the 330 km² Bwindi Impenetrable National Park in southwestern Uganda (Schaller 1963; Butynski 2001).

G. b. graueri (Matschie, 1914) is endemic to eastern DRC, and is found from the lowlands east of the Lualaba River and the Mitumba Range from Mount Tshiaberimu in the north of Virunga National Park, south to the Itombwe Massif, and formerly even further south in the area west of Fizi on the escarpment west of Lake Tanganyika (Schaller 1963; Butynski 2001; Mehlman 2008). The southern limit of the current Grauer’s Gorilla range has been extended by the discovery in late 2007 of a hitherto unreported population in the Hewa Bora region east of Kilembwe in Fizi District (J. Hart, pers comm.).
Countries:
Native:
Congo, The Democratic Republic of the; Rwanda; Uganda
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: G. b beringei

The Mountain Gorilla subspecies is found in only two isolated subpopulations in Rwanda, Uganda, and the DRC. The Virunga subpopulation was estimated at 380 individuals in 2003, an increase from 320 in 1989 (Gray et al. 2006). Approximately half of the subpopulation is mature individuals (Kalpers et al. 2003; Gray et al. 2006). However, all population growth in the Virungas between 1989 and 2003 has been limited to one sector of the population, the four gorilla groups in perhaps ecologically the richest area, which is also relatively well protected (Kalpers et al. 2003; Gray et al. 2006). Not only do unhabituated (and therefore less well-protected) groups have a lower ratio of juveniles to adults, but the current rate of growth of the whole population is lower than that during the 1980s (Kalpers et al. 2003). Additionally, a resurgence in poaching and killing of gorillas (approximately 3% of the entire Virunga subpopulation in 2007: see below) directly limits population growth and emphasizes the fragile nature of this small population.

While the G. b. beringei subpopulation in Bwindi Impenetrable National Park was believed to have increased from about 300 gorillas in 1997 to 320 individuals in 2003 (McNeilage et al. 2006), a census in 2006 that combined genetic analysis of the entire population with traditional census methods revealed that there are only approximately 300 individuals in Bwindi (Guschanski et al. in review). These new results do not lead to the conclusion that the population has declined in size; instead, due to the ‘sweep census’ method used, it is not possible to put error estimates around the population estimates and therefore it is difficult to assess how the population size has been changing over time.

In total, the subspecies G. b. beringei has only approximately 680 individuals remaining in two isolated populations.

G. b. graueri
In 1995, the population of G. b. graueri was estimated at 16,900 animals (Hall, Saltonstall et al. 1998; Hall, White et al. 1998). In the last decade, it is believed that the total population has declined dramatically, as the lowland populations have been progressively fragmented and reduced (Hart and Liengola 2005; Hart et al. 2007). Many populations have disappeared in the last 30 years (comparing Schaller 1963 and Hall, Saltonstall et al. 1998); for example, Itombwe lost about half of its subpopulations between 1960 and 1996 (Omari et al. 1999). Their habitat continues to become fragmented and discontinuous; the current occupancy range for Grauer’s Gorilla is estimated at 21,600 km², a decline of 25% from surveys completed in 1959 (Mehlman 2008). However, data are lacking to determine the extent of decline, apart from in the uplands of Kahuzi-Biega National Park, where the population dropped from an estimated 270 in 1996 to only 170 animals in 2000 (WCS 2000).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: The Mountain Gorillas of the Virunga Volcanoes are confined by surrounding cultivation to altitudes above 1,500 m, extending up perhaps to 4,000 m. That range of altitude covers many Afromontane habitat types, from bamboo forest to subalpine zones, typically with dense ground vegetation and relatively little canopy cover (Schaller 1963; Vedder 1984; Watts 1984). The Mountain Gorillas of Bwindi live at altitudes of 1,100-2,400 m, in a forest characterized by steep hills of predominantly mixed forest habitat with a dense understorey. While both subpopulations feed mainly on herbaceous vegetation, diet composition varies greatly with altitude, and the Bwindi gorillas incorporate a considerable amount of fruit into their diet (Ganas et al. 2004; Robbins et al. 2006).

G. b. graueri is distributed from lowland tropical rainforest habitat through transitional forests to Afromontane habitat (500–2800 m). G. b. graueri has a different diet from that of G. b. beringei, largely due to differences in what plant species are present, but they also feed predominantly on herbaceous vegetation, as well as on fruit from many species (Ferriss et al. 2005; Yamagiwa et al. 2005).
Systems: Terrestrial

Threats [top]

Major Threat(s): Detailed information on the threats to the Eastern Gorilla and its two subspecies can be found in chapters 8, 13 and 16 of Caldecott and Miles (2005).

G. b. beringei

For the Mountain Gorilla, G. b. beringei, the Virunga Volcanoes region and Bwindi Impenetrable NP are surrounded by some of the highest human densities in Africa (Plumptre and Williamson 2001; CIESIN and CIAT 2005) in countries with some of the fastest increasing human populations in Africa (World Resources Institute 2007). So many people with so much need for land pose significant threats to both subpopulations of Mountain Gorilla. While a key conservation strategy for both subpopulations of Mountain Gorillas is tourism, there is concern about the risk of disease transmission and disturbance to the gorillas, both of which could jeopardize these conservation programmes (e.g. Butynski and Kalina 1998; Homsy 1999). Transmission of infectious disease agents has been proven among habituated wild gorillas, people, domestic animals and other wild animals. Although not yet documented in gorillas, human-origin viral respiratory disease has recently been shown to cause high mortality among habituated chimpanzees (Köndgen et al. 2008). However, overall, Mountain Gorillas visited by researchers and tourists have consistently done better than those not visited, due to the level of protection afforded to areas and groups that are monitored daily (Harcourt 1986; Weber 1993). For instance, in both the 1981 census and 2003 census of the Virunga gorillas, the ratio of immatures to adults were higher in gorilla groups visited by researchers or tourists than in groups not visited (Harcourt et al. 1983; Gray et al. 2006), at 0.4 vs. 0.6 juveniles per non-silverback adult in 2001 (Gray et al. 2006, Table 3). Nevertheless, the threats remain considerable, and intensive conservation activities must continue.

The Virunga subpopulation of G. b. beringei suffered numerous impacts from more than a decade of war and instability in the region (Plumptre and Williamson 2001). Threats included incursions by militia, habitat destruction for firewood and farmland, illegal cattle grazing, illegal timber extraction, and illegal hunting, including snares set for other mammals such as antelope that can injure or kill gorillas. In 2004, 15 km² was deforested for conversion to farmland (NASA 2005) and recently there has been a sharp increase in timber extraction for the illegal production of charcoal. There has also been a resurgence of poaching for the illegal pet trade and bushmeat (Kalpers et al. 2003) and since 2003, 12 orphans (both Grauer’s and Mountain Gorillas) have been confiscated and taken into the care of veterinarians. In 2007, at least eight gorillas were shot dead in three incidents in Virunga NP (Williamson and Fawcett 2008). These losses amount to about 3% of the Virunga subpopulation. Since September, the Mikeno sector, where DRC’s Mountain Gorillas are found, has been under rebel control and park authorities have been prevented from monitoring the gorillas. The failure of the 2008 Peace Conference means that the region remains volatile and the gorillas vulnerable, despite the efforts of international NGOs and UN observers.

Threats to the Bwindi subpopulation of G. b. beringei include illegal use of forest resources (poaching, pit-sawing, firewood collection, etc.), encroachment and demand for land, human-induced fires, invasive exotic species and human-wildlife disease transmission (McNeilage et al. 2006). The forest is also recovering from high levels of timber extraction, gold-mining, encroachment and poaching that occurred prior to designation of National Park status in 1991.

G. b. graueri

In eastern DRC, Grauer’s Gorillas face substantial threats to their survival: agriculture and pastoral activities are leading to massive loss and fragmentation of forest habitat (as noted already, the current occupancy range for Grauer’s Gorilla is approximately 21,600 km², a decline of 25% since 1959; Mehlman 2008); widespread illegal mining activities in the forests increase demand for bushmeat, including consumption of gorillas; and illegal capture of infants (and concomitant killing of group members), which has increased substantially since 2002. Ongoing political unrest and military activity, including occupation of national parks, and killing of gorillas for food, have compounded the problems (Hall, Saltonstall et al. 1998; Plumptre et al. 2003; Yamagiwa 1999, 2003). At present, there is no commercial logging in the Grauer’s range, but there are continuous low-level extractive activities (charcoal production, bamboo harvesting and wood cutting), which put further stress on the habitat (J. Hart pers. comm. 2007). As some of the country emerges from civil war, new concessions for timber, minerals, and possibly petroleum will pose conservation challenges for the future (Caldecott and Miles 2005, Ch. 16).

Conservation Actions [top]

Conservation Actions: Detailed information on conservation measures to protect the Eastern Gorilla and its two subspecies can be found in chapters 8, 13 and 16 of Caldecott and Miles (2005).

The Eastern Gorilla is listed under Class A of the African Convention and Appendix I of CITES. The subspecies is found only within National Parks. These protected areas all have active national programmes for conservation management, assisted by international NGOs. Although the protected areas are relatively well monitored, measures of the impacts of illegal activities on the gorillas should continue.

Most subpopulations of G. b. graueri are found in protected areas, where international NGOs are supporting rehabilitation and conservation programmes, such as in Kahuzi-Biega NP, Maïko NP, Tayna Nature Reserve and Kisimba-Ikobo Nature Reserve. However, due to the presence of armed militia groups in some areas, conservation activities sometimes require assistance from the United Nations Mission in the Congo (MONUC). Efforts are underway to establish up-to-date distribution, abundance, and threats to improve conservation management. It is important to identify key populations of G. b. graueri and continue to provide active protection. Work must continue to document the post-conflict distribution, abundance and conservation status of Grauer’s Gorilla throughout its range. Efforts must also be made to support and maintain active protection for Grauer’s Gorilla where it is already established, while simultaneously developing and mobilizing conservation activities in the more remote and inaccessible sectors of its range.

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Citation: Robbins, M. & Williamson, L. 2008. Gorilla beringei. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 23 September 2014.
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