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Gorilla gorilla ssp. diehli

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA PRIMATES HOMINIDAE

Scientific Name: Gorilla gorilla ssp. diehli
Species Authority: Matschie, 1904
Parent Species:
Common Name(s):
English Cross River Gorilla
Synonym(s):
Gorilla gorilla subspecies stock
Taxonomic Notes: The Western Gorilla (Gorilla gorilla) consists of two recognized subspecies: Gorilla gorilla gorilla (Western Lowland Gorillas) and Gorilla gorilla diehli (Cross River Gorillas). The taxonomic status of the gorilla populations in the Maiombe Forest (Cabinda, Democratic Republic of Congo and Republic of Congo) and in Ebo/Ndokbou (Cameroon) awaits clarification; however, measurements from a single Ebo gorilla skull indicate this may be a relict population of a previously more widespread population living north of the Sanaga River (Groves 2005).

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A4cd ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Oates, J.F., Bergl, R.A., Sunderland-Groves, J. & Dunn, A.
Reviewer(s): Mittermeier, R.A., Williamson, E.A. & Butynski, T.M. (Primate Red List Authority)
Justification:
Listed as Critically Endangered since the total number of mature individuals is probably less than 200. There is the strong probability of continuing decline based on continuing loss, degradation and fragmentation of habitat from farming and road construction, and at least a low level of hunting. Also, there are fewer than 50 mature individuals in each of the subpopulations. The remaining total number of Cross River gorillas is estimated at 250 to 300 individuals spread between 9 to 11 localities including the recently-discovered population isolate in the Bechati area (Groves 2002, Oates et al. 2003, Beamont 2004, Bergl 2006). Genetic data suggest that gorillas in many of the Cross River localities are still in tenuous reproductive contact through the exchange of occasional migrants (Bergl and Vigilant 2007).
History:
2007 Critically Endangered
2000 Critically Endangered
2000 Critically Endangered
1996 Critically Endangered
1996 Critically Endangered

Geographic Range [top]

Range Description: G. g. diehli (Matschie, 1903) occurs in a small area on the Nigeria-Cameroon border, extending a short distance on either side of the border in the forests on the upper drainage of the Cross River.
Countries:
Native:
Cameroon; Nigeria
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Although gorillas in the Cross River region first became known to science in the early 20th century, little attention was paid to their conservation status until the late 1980s (Harcourt et al. 1989). Early reports had referred to their precarious situation, but little had been done to thoroughly examine their distribution and abundance, or to protect the remaining population and habitat (Anon 1934, Critchley 1968, March 1957). Intensive surveys over the last decade have found that approximately 250 to 300 G. g. diehli persist in a forested area of roughly 8,000 km². This estimate is of uncertain accuracy and is based primarily on nest counts and estimated range size. The gorillas are found in at least 10 localities (Groves 2002, Beamont 2004, Bergl 2006, Bergl and Vigilant 2007). Though the localities where the gorillas are found are geographically distinct, the majority of these areas are connected by forested land. Recent genetic evidence suggests that three subpopulations are present, but that these subpopulations do have limited reproductive contact (Bergl and Vigilant 2007). These localities are primarily rugged highlands, typically in areas relatively less disturbed by human activity. While there may be an ecological component to this distribution, the gorilla’s concentration in highland areas is almost certainly strongly influenced by human hunting pressure, which is more intense in the lowlands. Ebola has not been reported in the G. g. diehli population, but their close proximity to dense human populations puts them at high potential risk of acquiring human pathogens (Oates et al. 2007).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Two studies of G. g. diehli (at Afi and Kagwene) demonstrated flexible grouping patterns with groups ranging in size from 2 to 20. These grouping patterns likely occur for several reasons, including restricted habitat, feeding competition related to fruit consumption, high hunting pressure, and limited opportunities for male migration between nuclei (McFarland 2007). Each group’s home range may be as large as 20 km² and group ranges overlap extensively. Today, Cross River gorillas are restricted mostly to hilly areas, and range from lowland to submontane forest (Allen 1932, Oates et al. 2003, Sunderland-Groves et al. 2003), although they occasionally use lowland areas between hills (Oates et al. 2003, Bergl 2006).
Systems: Terrestrial

Threats [top]

Major Threat(s): The remaining population of G. g. diehli is small and fragmented, occurs mostly outside of protected areas (especially in Cameroon) and is surrounded by some of the most densely populated human settlements in Africa. This subspecies is at risk from its small size and associated increases in inbreeding and loss of genetic diversity. The lack of strictly protected areas throughout much of the range of G. g. diehli makes the future of sizeable portions of gorilla habitat uncertain. Conversion of forest for agriculture and grazing is occurring rapidly in many parts of the gorillas’ range and the largest current protected area in which Cross River gorillas occur (the Okwangwo Division of Nigeria’s Cross River National Park) contains enclaves of human settlements whose farmlands have spread beyond their legal boundaries and threaten to divide the park into two. The construction and improvement of roads in both Cameroon and Nigeria also threatens to increase subdivision of the population. Though legal prohibitions against the killing of gorillas exist in Nigeria and Cameroon, enforcement of wildlife laws is often lax, and most protected areas suffer from poorly-controlled poaching. Although recent conservation efforts have reduced hunting of Cross River gorillas to a low level, the threat remains and the small size of the G. g. diehli population means that almost any level of hunting off-take is likely to be unsustainable and have a significant negative effect on population size.

Conservation Actions [top]

Conservation Actions: A series of three workshops has identified priority actions for the conservation of G. g. diehli, and these have been formulated into an IUCN Action Plan (Oates et al. 2007). There are several cross-cutting actions which require attention throughout Cross River gorilla range, notably increasing conservation education and awareness, fostering improved community participation in conservation issues, increasing trans-boundary conservation activities such as joint patrols to control timber and bushmeat between the two countries, and further research. The most urgently-needed actions identified, which must be undertaken for any longer-term measures to be effective, are habitat protection and the control of hunting. In Nigeria the majority of the G. g. diehli population occurs within formal protected areas (Cross River National Park and Afi Mountain Wildlife Sanctuary), but in Cameroon none of the population is as yet protected in this way (although two areas are in process of establishment: Takamanda National Park and Kagwene Gorilla Sanctuary). Further areas, including migration corridors, need to be brought under conservation management to increase the chances for the long-term survival of a viable population of Cross River gorillas, and the effectiveness of existing management improved.

Citation: Oates, J.F., Bergl, R.A., Sunderland-Groves, J. & Dunn, A. 2008. Gorilla gorilla ssp. diehli. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 28 November 2014.
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