|Scientific Name:||Gorilla beringei Matschie, 1903|
|Infra-specific Taxa Assessed:|
|Taxonomic Source(s):||Mittermeier, R.A., Rylands, A.B. and Wilson D.E. 2013. Handbook of the Mammals of the World: Volume 3 Primates. Lynx Edicions, Barcelona.|
|Taxonomic Notes:||This species appeared in the 1996 Red List as a subspecies of Gorilla gorilla. Since 2001, the Eastern Gorilla has been considered a separate species (Gorilla beringei) with two subspecies: Grauer’s Gorilla (Gorilla beringei graueri) and the Mountain Gorilla (Gorilla beringei beringei) following Groves (2001).|
|Red List Category & Criteria:||Critically Endangered A4bcd ver 3.1|
|Assessor(s):||Plumptre, A., Robbins, M. & Williamson, E.A.|
|Reviewer(s):||Mittermeier, R.A. & Rylands, A.B.|
|Contributor(s):||Butynski, T.M. & Gray, M.|
Eastern Gorillas (Gorilla beringei) live in the mountainous forests of eastern Democratic Republic of Congo, northwest Rwanda and southwest Uganda. This region was the epicentre of Africa's "world war", to which Gorillas have also fallen victim. The Mountain Gorilla subspecies (Gorilla beringei beringei), has been listed as Critically Endangered since 1996. Although a drastic reduction of the Grauer’s Gorilla subspecies (Gorilla beringei graueri), has long been suspected, quantitative evidence of the decline has been lacking (Robbins and Williamson 2008). During the past 20 years, Grauer’s Gorillas have been severely affected by human activities, most notably poaching for bushmeat associated with artisanal mining camps and for commercial trade (Plumptre et al. 2015). This illegal hunting has been facilitated by a proliferation of firearms resulting from widespread insecurity in the region. Previously estimated to number around 16,900 individuals, recent surveys show that Grauer’s Gorilla numbers have dropped to only 3,800 individuals – a 77% reduction in just one generation (ibid.) This rate of population loss is almost three times above that which qualifies a species as Critically Endangered.
The roughly 880 Mountain Gorillas have been faring substantially better; one of the two subpopulations is recovering from an all-time low in the 1980s, making Mountain Gorillas the only great ape taxon that has been increasing in number (Gray et al. 2013). In 2016, a census was ongoing and genetic analyses will confirm whether or not the Virunga population is still growing. Therefore, the Gorilla beringei beringei subspecies account will not be updated until the results of the 2016 survey are available. Meanwhile, Grauer's Gorillas are declining at an average rate of 5% per year (Plumptre et al. 2015). If this continues unabated, about 93% of Eastern Gorillas will be gone by 2054 (three generations from 1994). Even if the Mountain Gorilla population continues to grow, an overall continuation of the decline of Eastern Gorillas is expected due to the high levels of poaching, loss of habitat as human populations expand, and civil unrest and lawlessness in parts of this species’ geographic range. Therefore, Eastern Gorillas qualify as Critically Endangered under criterion A (A4bcd).
|Previously published Red List assessments:|
|Range Description:||Eastern Gorillas are found in eastern Democratic Republic of Congo (DRC), northwest Rwanda and southwest Uganda.|
Gorilla beringei beringei (Matschie 1903) is restricted to two populations in forests only 25 km apart, but isolated by land that is intensely cultivated and densely settled. One population is in the Virunga Volcanoes, straddling the borders between DRC (Virunga National Park), Rwanda (Volcanoes National Park) and Uganda (Mgahinga Gorilla National Park). The other occurs in Bwindi Impenetrable National Park, Uganda, with a small contiguous portion in Sarambwe Nature Reserve in DRC.
Gorilla beringei graueri (Matschie 1914) is endemic to the forests of the Albertine Rift escarpment in eastern DRC. It has a discontinuous distribution from the lowlands east of the Lualaba River to the Mitumba Mountains and the Itombwe Massif. Mt. Tshiaberimu in Virunga National Park is the northern limit of Grauer’s Gorilla’s geographic range. The southern limit is a subpopulation in the Hewa Bora region, Fizi District (Plumptre et al. 2009).
Although formerly known as the Eastern Lowland Gorilla, G. b. graueri occurs over the widest altitudinal range of any Gorilla, from approximately 600 m to 2,900 m asl, overlapping considerably with the altitudinal range of G. b. beringei (1,100–3,800 m asl; Williamson et al. 2013).
Native:Congo, The Democratic Republic of the; Rwanda; Uganda
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||It is likely that fewer than 5,000 Eastern Gorillas remain. The most recent estimate for Mountain Gorillas is 880 individuals living in two isolated populations in DRC, Rwanda and Uganda (Gray et al. 2013, Roy et al. 2014), making them only great ape taxon that has been increasing in number (Gray et al. 2013). In 2016, new surveys were ongoing and genetic analyses will confirm whether or not the Virunga population is still growing. Therefore, the G. b. beringei subspecies account will not be updated until the results of the 2016 survey are available.|
In 1995, the total population of G. b. graueri was estimated to be 16,900 individuals (Hall et al. 1998a, 1998b). Since then, widespread insecurity and poaching for bushmeat, particularly around mining camps, have led to increasing fragmentation of the population and reduction of numbers. Using survey data collected between 2010 and 2015, Plumptre et al. (2015) estimated that the total number of Grauer's Gorillas remaining in 2015 is only 3,800—a 77% loss since 1994. These population estimates were made using night nest abundance and distribution, and predictive modelling. Nest encounter rates indicate an ongoing rate of decline of ~5% per year at many of the sites surveyed, due to fragmentation and illegal hunting around the many artisanal mining camps and villages located in areas where Grauer's Gorillas occur (Plumptre et al. 2015).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Grauer's Gorillas range between 600 and 2,900 m asl in dense mature and secondary lowland tropical rainforest through transitional forests to Afromontane habitat, including bamboo forest, swamp and peat bog. Mountain Gorillas are restricted to elevations above 1,100 m in Bwindi Impenetrable National Park and above 1,850 m in the Virungas by human occupation at lower levels. Their habitat includes many Afromontane vegetation types, including bamboo forest, mixed forest, and subalpine grassland on the volcanic peaks. The Bwindi Mountain Gorillas live at lower elevations, in forest characterised by steep slopes of predominantly mixed forest habitat with a dense understorey.|
Diets of Eastern Gorillas vary greatly with elevation and its effect on food availability. Mountain Gorillas are largely herbivorous and feed on stems, pith, leaves, bark, and occasionally ants. Their favoured food items are wild celery, thistles, nettles, bedstraw, wood and roots. Both subspecies feed almost exclusively on young bamboo shoots when they are in season twice a year. Gorillas at lower elevations have a more diverse and seasonal diet. Both Grauer’s Gorillas in lowland forest and Bwindi Gorillas are frugivorous.
Eastern Gorillas are diurnal and semi-terrestrial. After waking, they feed intensively and then alternate rest, travelling and feeding until night-time. All Gorillas build nests to sleep in, some in trees, but the majority of their nests are on the ground. Gorillas are not territorial, and there is extensive overlap between the annual home ranges of different groups, which vary in size from 6–40 km². Eastern Gorilla groups are polygynous or polygynandrous, with one or more adult males, several females, their offspring, and immature relatives forming the core of relatively stable groups. Median group size is 10 weaned individuals; maximum observed group size is 65 individuals.
Life History (as summarised in Williamson and Butynski 2013)
Male Eastern Gorillas are capable of reproducing when they become “blackbacks” at 8-12 years of age. They are considered “silverbacks” at 12 years of age, and reach their full adult size at 15 years. Female menarche occurs at 6-7 years of age, followed by a period of adolescent sterility. Average age of first parturition is 9.9 years. Females have a reproductive cycle of ca 28 days and are receptive for 1-4 days around the time of ovulation. They experience lactational amenorrhea while suckling infants. Young are weaned at 3-4 years of age, from which point they no longer travel on their mothers’ back. Females give birth every 3-4 years and generally produce 3-4 surviving offspring during their reproductive life span. Maximum life span is unknown, but it is certainly over 40 years. Eastern Gorillas have a generation time of 18.2 years for females and 20.4 years for males (Langergraber et al. 2012).
|Generation Length (years):||20|
|Movement patterns:||Not a Migrant|
|Use and Trade:||
Gorillas are completely protected by national and international laws in all countries of their range, and it is, therefore, illegal to kill, capture or trade in live Gorillas or their body parts.
Major threats to Eastern Gorillas are:
Gorilla beringei is listed under Class A of the African Convention and Appendix I of CITES. DRC has a legal framework for managing national parks and wildlife, but has difficulty applying its laws, and political will is limited. Underlying this is a difficult sociopolitical context – a breakdown of law and order during two decades of conflict, combined with poverty and economic insecurity, exacerbates the difficulties of enforcing the law in this region. To address the critical situation faced by Grauer’s Gorillas, NGOs are working with the government authorities to support protected areas and reinforce conservation programmes. However, the widespread presence of armed groups in eastern DRC restricts the ability of conservation organisations to operate in the field.
One quarter of the predicted range of the Grauer’s Gorillas occurs in national parks and nature reserves; the remaining three quarters is currently unprotected (Plumptre et al. 2015). Gazetting of the Itombwe Reserve and establishing a protected area west of Kahuzi-Biega National Park could secure as much as 50% of the subspecies' range.
Conservation challenges are likely to increase as the DRC government continues its efforts to stabilize the east. Security will favour industrial extraction, large-scale agriculture and infrastructure. While development will increase the country's ability to support its human population and participate in the global economy, it will also result in increased human settlement in forest areas critical to Gorillas. Targeted conservation action in priority sites will be vital to slow further demise of this subspecies.
The entire Mountain Gorilla population resides in protected areas where there are active government programmes. Although the protected areas are relatively well monitored, illegal activities continue in some locations, therefore monitoring the impacts of both illegal activities and conservation actions should continue. While these national parks are legally protected, habitat fragmentation and degradation will be exacerbated if infrastructure developments are allowed within their boundaries.
To achieve conservation successes, long-term commitment is key, as shown by the international conservation organisations that have been working in difficult circumstances for decades to support the protected area authorities and try to secure the survival of Eastern Gorillas. IUCN has published a detailed conservation strategy with clear priorities for Grauer’s Gorillas (Maldonado et al. 2012). See Plumptre et al. (2015) for additional recommendations and see Robbins et al. (2011) for an overview of the impacts of conservation activities on mountain Gorillas in the Virunga Massif.
|Errata reason:||This is an errata version of the 2016 assessment to address minor grammatical corrections to the Geographic Range and Population sections.|
|Citation:||Plumptre, A., Robbins, M. & Williamson, E.A. 2016. Gorilla beringei (errata version published in 2016). The IUCN Red List of Threatened Species 2016: e.T39994A102325702.Downloaded on 16 January 2018.|
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