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Conserving the Most Endangered Gorilla
Photo Credit: Nicky Lankester, Limbe Wildlife Centre
by Aaron Nicholas, Andrew Dunn, and Dirck Byler
Great apes capture our imagination in part because of their remarkable similarity to humans. In habitats spanning the equatorial areas of West and Central Africa, as well as Southeast Asia, apes serve as flagship species for complex ecosystems that support a wide array of animals and plants. All of these highly intelligent, charismatic ape species face a combination of threats: habitat destruction, hunting, disease, and conflict with people. The U.S. Fish and Wildlife Service’s Great Ape Conservation Fund (WWB-GACF), part of the Wildlife Without Borders program, supports projects to address these threats. At the same time, the fund helps to build the human and institutional capacity necessary to improve the status of ape populations worldwide.
Research supported by WWB-GACF has yielded exciting advances in our understanding of apes, including evidence of sophisticated tool use techniques by chimpanzees, dietary needs and habitat preferences, protocols to prevent disease and limit transmission, improved law enforcement, and trans-boundary ranger-based monitoring systems. It has worked with partners in nearly all 22 of the countries in which apes are found.
One of Africa’s emblematic great apes is the gorilla. Four subspecies are acknowledged today: the Eastern lowland gorilla, mountain gorilla, Western lowland gorilla, and Cross River gorilla (the most western and northern form). The Cross River gorilla (Gorilla gorilla diehli) is the most critically endangered subspecies. With a population less than half of its better known cousin, the mountain gorilla (Gorilla beringei beringei), it is perhaps surprising that the plight of the Cross River gorilla is not more widely known.
Back from the Brink
Inhabiting a remote corner of West Africa that straddles the border of Nigeria and Cameroon, the Cross River gorilla was once largely neglected by conservationists. Many believed it was likely extinct (Cousins, 1978) until its rediscovery in the early 1980s (Oates 1999). In recent years, our understanding of the Cross River gorilla has benefited from systematic surveys and field studies of its ecological and behavioral characteristics. The bad news is that we now believe fewer than 300 Cross River gorillas remain, distributed in about 12 discrete mountain refuges across a landscape the size of Connecticut. Based on the small population, its fragmentation across a large landscape, and the threats posed by habitat destruction and hunting, the Cross River gorilla is recognized by the International Union for the Conservation of Nature (IUCN) as "critically endangered."
Photo Credit: Dirck Byler, USFWS
Challenges to conservation
The challenge we face is how to develop an effective conservation strategy for a highly fragmented, slowly reproducing population of great apes distributed across two countries in a region containing some of the highest human population densities in Africa. At the local level, hunting of gorillas to fuel the region’s bushmeat trade and the continuing erosion of habitat connectivity remain the greatest obstacles to conservation.
Although the number of Cross River gorillas has declined rapidly in the past hundred years or so, probably because of the introduction of hunting with firearms, the outlook is far from bleak. Carefully planned, painstaking research over the last few years provides renewed hope and direction for conservation. After conservationists and researchers raised awareness about the bushmeat problem, the hunting of Cross River gorillas dropped to a low level, but it is still a potential threat, as are wire-snare traps set for other animals.
As recently as 2005, conservationists were unsure if the geographic division of the population had already weakened the genetic pool. No information on the viability of apparently isolated groups of gorillas was available. However, recent work by Dr. Richard Bergl of the North Carolina Zoo revealed encouraging findings (Bergl and Vigilant, 2006) on gorilla genetics. Based on DNA analyses of material collected from gorilla feces, he found that the Cross River population showed clear evidence of genetic sub-division into three main groups. Evidence from the 71 gorillas he studied confirmed that individuals continue to move among certain sites. Overall, the genetic diversity of the Cross River gorilla population is comparable to two mountain gorilla populations in the Virunga Mountains and Bwindi National Park. Even more encouraging is the fact that Cross River gorillas have much more viable habitat available than their mountain kin to the east, so there is potential for population recovery.
Since 2004, with support from WWBGACF, the Wildlife Conservation Society has undertaken numerous field surveys to complete the picture of Cross River gorilla distribution. Based on spatial models developed by Bergl that predict gorilla distribution and connectivity, the results from these surveys have been encouraging. Gorilla sign has been found in numerous locations between previously known sites, confirming that connectivity remains.
Working together to solve the puzzle
Photo Credit: Aaron Nicholas/WCS
Since the development of a Regional Action Plan for the Conservation of the Cross River Gorilla (Oates et al. 2007), work has been rapid. Today, many key Cross River gorilla sites are under some form of formal or community-based protection, although the effectiveness varies. In 2008, support from the Great Ape Conservation Fund helped the Cameroon government create two new protected areas – the Kagwene Gorilla Sanctuary and Takamanda National Park – that will benefit roughly one-quarter of all known Cross River gorillas. Additionally, with support from WWB-GACF and the Arcus Foundation, the Wildlife Conservation Society launched a trans-boundary management program that brings government staff from Cameroon and Nigeria together to characterize, prioritize, and protect the habitat corridors linking key Cross River gorilla sites. The WWBGACF has identified the Cross River gorilla’s range as a priority landscape, and it plans to intensify efforts to engage local stakeholders in gorilla protection. It will also increase training opportunities for wildlife conservation staff in government and local organizations.
For the first time in decades, we believe there is real hope for the Cross River gorilla.
Bergl, R.A. and Vigilant, L. 2007. Genetic analysis reveals population structure and recent migration within the highly fragmented range of the Cross River gorilla (Gorilla gorilla diehli). Molecular Ecology 16: 501-516.
Cousins, D. 1978. Gorillas – A Survey. Oryx 14: 254-258.
Harcourt, A.H., Stewart, K.J. and Inahoro, I. 1989. Gorilla Quest in Nigeria. Oryx 23:7-13.
Groves, J.L. 2001. Gorillas of Takamanda, Mone and Mbulu forest, Cameroon. Gorilla Journal 22: 27-29.
Oates, J. F. 1999. Myth and Reality in the Rainforest. University of California Press: Berkeley.
Oates, J., et.al. 2007. Regional Action Plan for the Conservation of the Cross River Gorilla (Gorilla gorilla diehli). IUCN/SSC Primate Specialist Group and Conservation International, Arlington, VA, USA.
Aaron Nicholas is Director of the Wildlife Conservation Society’s Takamanda-Mone Landscape Project in Cameroon. Andrew Dunn is the Nigeria Coordinator for the Wildlife Conservation Society. Dirck Byler is the program officer for the U.S. Fish and Wildlife Service’s Great Ape Conservation Fund and Wildlife Without Borders-Africa.
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