Western gorilla re-introduction to the Batéké Plateau region of Congo and Gabon

By: Tony King and Amos Courage

The Aspinall Foundation, 2008 [view pdf version]

 Published in: Soorae, P. S. (ed.), 2008. Global re-introduction perspectives: re-introduction case-studies from around the globe. IUCN/SSC Re-introduction Specialist Group, Abu Dhabi, UAE. Pp. 217-220. Available from:http://www.iucnsscrsg.org/


The western gorilla (Gorilla gorilla gorilla) is classified by IUCN (2007) as Critically Endangered due to past and current rapid population decline, and is listed on CITES Appendix I. The UK-based charity The Aspinall Foundation is coordinating the re-introduction of the species to the Batéké Plateau region of the neighboring Republics of Congo and Gabon, from where it has been extirpated during the past few decades. This is being undertaken within the framework of the Projet Protection des Gorilles (PPG), initiated in co-operation with the respective governments in Congo in 1987, and in Gabon in 1998. The overall mission of PPG is “to work with local partners for the conservation of indigenous endangered species in general, and of gorillas in particular”. Gorilla re-introduction is one of the activities of PPG to realise this mission. The current re-introduction sites are the south-west Lefini Reserve in Congo, and the Batéké Plateau National Park (PNPB) in Gabon. The two protected areas are approximately 200 km apart, and are subject to collaborative management projects as a result of the re-introduction program.


        Goal 1: To re-introduce viable, self-sustaining populations of western gorillas within their former range.

        Goal 2: To ensure effective long-term management of the release sites within legally protected areas.

Success Indicators

        Indicator 1: High post-release survival of released individuals.

        Indicator 2: Successful adaptation of released individuals to release site.

        Indicator 3: Exhibition of social and other behaviors similar to those observed in wild populations.

        Indicator 4: Reproduction within the re-introduced populations.

        Indicator 5: Long-term persistence of the re-introduced populations.

        Indicator 6: Improved legal status of the release sites.

        Indicator 7: Effective management of the release sites leading to ecosystem recovery.


Project Summary

Planning for the program commenced in Congo in the late 1980s, with a cautious approach taken. Various risks involved were recognized and plans were developed accordingly. Risks to released individuals were minimized through soft-release strategies and intensive post-release monitoring. Risks to wild populations were virtually eliminated by selecting release sites where great apes had been locally extirpated, and other primates were at low densities, and by long-term medical assessments of release stock. The sites selected represented relatively degraded ecosystems, for which the re-introduction of gorillas was considered beneficial, both in terms of the significant ecological role that the species has been shown to fulfil in central African forests, and through the associated site management activities. The Batéké Plateau supports a fragile ecosystem, with large expanses of nutrient-poor savanna soils and a growing human population heavily reliant on natural resources. The maintenance of ecosystem functioning is therefore of great importance within the socio-economic situation of the region. Long-term political, technical and financial support were considered crucial to the success of such an ambitious program, so both projects benefit from co-operative partnerships between the respective governments and The Aspinall Foundation.

The Aspinall Foundation manages the largest and most successful breeding colony of gorillas in captivity, at the Howletts and Port Lympne Wild Animal Parks in UK, and is fully committed to supporting the re-introduction program in the longterm. The release stock consists primarily of wild-born gorillas orphaned by the illegal bush-meat trade and confiscated by the national governments. Usually less than three years-old at arrival, the gorillas undergo a lengthy period of rehabilitation and preparation prior to full release. The Gabon release stock has been supplemented by hand-reared captive-born individuals transferred from UK, who also require lengthy pre-release preparation. Rehabilitation and preparation is a complex process that includes aspects such as psychological support, social integration, forest adaptation, behavioral and health assessments, and occasional medical interventions.

The gorillas are released in groups established during the preparation phase. Group composition has generally been influenced by the availability of suitable release stock during the pre-release preparation, and group size at release has ranged from three to seventeen individuals. The first releases took place in 1996, followed by further releases in 1998 and 2001, in the Lesio-Louna Reserve in Congo. Despite high post-release survival and successful adaptation to the site, this first attempt was finally abandoned due to the lack of major ecological barriers between the released gorillas and human activity. Large rivers appear to be the most suitable barriers, and are now used in both Congo and Gabon to separate released gorillas from villages, project camps and local-use zones, although intervention strategies are kept available if necessary. All the surviving gorillas released in the Lesio-Louna were gradually recaptured, and most were rereleased in the new site in the neighboring south-west Lefini Reserve in 2003 and 2004. A further three sub-adult females were added to this population in 2006. In the PNPB in Gabon, two groups have been released, in 2001 and 2004. Further releases are planned at both sites.

Post-release monitoring is undertaken by trained national staff using direct and indirect tracking techniques. Initially highly intensive, monitoring is gradually reduced for each group over time to decrease the impact of human presence on gorilla behavior, until it consists simply of a daily or weekly assessment of group ranging, composition and general health. Medical intervention is rarely necessary or even possible, but has been undertaken in some cases. Initial results are encouraging. A total of 51 gorillas have been released between 1996 and 2006, 25 in Congo and 26 in Gabon, consisting of 43 wild-born orphans, plus one in situ and seven ex situ hand-reared captive-born individuals. Overall post-release survival rates are high, at 84% in Congo and 84.6% in Gabon, and have been similar for males and females and for wild-born and captive-born. Other indications of program success include the observed feeding patterns of the released gorillas which include over 100 species of natural food plants, the ranging behavior of the released groups which is similar to that of wild western gorillas, and the exhibition of natural social behaviors such as female transfer and male dispersal. However, probably the highlight of the program so far has been the birth of six babies to re-introduced groups in the past four years. The baby born to the youngest of the six mothers, at 8.5 years-old, disappeared after six weeks, but the first to be born, to a 16.5 year-old, is now over 3.5 years and in good health. Given the slow life-histories of gorillas and the ongoing release stage, it is still too early to judge long-term population persistence. At the site level, two protected areas have been created through the program, and both, plus another formerly neglected protected area, are now subject to collaborative longterm management projects.


Major difficulties faced


Major lessons learned


Success of project: Highly Successful; Successful; Partially Successful; Failure

Reasons for success:

        Highly successful in terms of survival, adaptation and reproduction of released gorillas, and facilitation of protected area management projects.

        It is too early to conclude that the goal of “re-establishing viable, selfsustaining populations” has been realized.


For more information please consult:

King, T., Chamberlan, C. & Courage, A. 2012. Assessing initial reintroduction success in long-lived primates by quantifying survival, reproduction and dispersal parameters: western lowland gorillas (Gorilla gorilla gorilla) in Congo and GabonInternational Journal of Primatology 33 (1): 134-149.

King, T., Chamberlan, C., Pearson, L. & Courage, A. 2009. Gorilla sanctuaries and conservation in Congo and GabonInternational Zoo News 56 (6): 342-352.

King, T. 2008. Detectability and conservation of De Brazza’s monkey (Cercopithecus neglectus) in the Lesio-Louna and south-west Lefini Reserves, Bateke Plateau, Republic of CongoPrimate Conservation 23: 39-44.

King, T. 2008. A multidisciplinary approach to western gorilla reintroduction and ecosystem restoration in Congo and Gabon. Poster presented at the First International Wildlife Conference, Lincoln Park Zoo, Chicago, April 2008 (poster abstract #26). [poster]. Abstract available from:http://www.lpzoo.org/reintroworkshop/poster.html

King, T. 2008. Minimising risks and maximising benefits in a reintroduction programme in Central Africa (Poster Abstract). Avian Biology Research 1(1): 44.

King, T. & Chamberlan, C. 2008. Dispersal and reproduction in reintroduced western gorillas (Gorilla g. gorilla). Primate Eye 96: 301 (abstract #842).

King, T. & Chamberlan, C. 2008. Introduction of three sub-adult female western gorillas to a reintroduced silverbackGorilla Gazette 21: 37-40.

Pearson, L., Aczel, P., Mahé, S., Courage, A. & King, T. 2008. Gorilla reintroduction in Gabon. Gorilla Gazette 21: 41-44.

Pearson, L. & King, T. 2008. Reproduction in a second population of reintroduced western gorillas. Oryx 42 (1): 14.

King, T. & Chamberlan, C. 2007. Orphan gorilla management and reintroduction: progress and perspectives. Gorilla Journal 34: 21-25.

King, T. & Chamberlan, C. 2007. Gestion et réintroduction de gorilles orphelins : progrès et perspectives. Gorilla Journal 34: 22-26.

King, T. & Courage, A. 2007. Reintroduced western gorillas reproduce again. Oryx 41 (1): 14.

King, T., Chamberlan, C., Pearson, E. & Courage, A., 2006, Western gorilla (Gorilla g. gorilla) reintroduction to the Bateke Plateaux and the challenge of tourism (Abstract). International Journal of Primatology 27 (S1): #486.

King, T., Chamberlan, C. & Courage A. 2006. Gorilla reintroduction, Republic of Congo. A report for the PASA/IUCN African Primate Reintroduction Workshop, 20-22 April 2006, Apeldoorn, Netherlands, 17 p.

King, T., Chamberlan, C. & Courage, A., 2005, Reintroduced gorillas: Reproduction, ranging and unresolved issues. Gorilla Journal 30: 30-32.

King, T., Chamberlan, C. & Courage, A., 2005, Gorilles réintroduits : reproduction, domaine vital et questions irrésolues. Gorilla Journal 30: 30-32.

King, T., Chamberlan, C. & Courage, A., 2005, Rehabilitation of orphan gorillas and bonobos in the Congo. International Zoo News 52(4): 198-209.

King, T., 2005, Letters: King Congo. BBC Wildlife 23 (13): 94.

King, T., 2005, Gorilla reintroduction programme, Republic of CongoGorilla Gazette 18: 28-31.

King, T., 2005, Lengui, victim of the bushmeat trade: Twice. Gorilla Gazette 18: 31-33.

King, T., 2004, Reintroduced western gorillas reproduce for the first time. Oryx 38 (3): 251-252.

King, T., Boyen, E. & Muilerman, S., 2003, Variation in reliability of measuring behaviours of reintroduced orphan gorillasInternational Zoo News 50 (5): 288-297.

King, T., 2003, Letter: Bonobo victims. BBC Wildlife 21 (7): 86.