Minimizing competition by removing elephants from a degraded Ngulia rhino sanctuary, Kenya

Abstract

The Ngulia rhino sanctuary located in the central part of Tsavo West National Park (NP) is completely fenced within an area of 88 km 2 following its expansion from 62 km 2 in May 2007. It has been one of the more successful areas for the protection and breeding of black rhinos in Kenya since its creation in 1986, and has succeeded in re-establishing a productive breeding nucleus of rhinos within a larger protected area with very considerable potential for further expansion to a large, genetically viable population. The sanctuary therefore plays a key role in the conservation of the eastern black rhinoceros (Diceros bicornis michaeli).

Following concerns about the deteriorating vegetation condition in the sanctuary (fig. 1), detailed analysis of population data and assessment of habitat showed a 59% decline in the available rhino browse between 1991 and 2005 (rhino food plants i.e. below 2 m high) and 100% decline of browse material above 2 m height (fig. 2). The analysis also showed that the rhino population performance had been significantly declining over several years due to high densities of rhinos (fig. 3a) and competing browsers particularly elephants (table 1). The annual growth rate had fallen to below the minimum national target of 5% (Okita-Ouma and Wandera 2006) and the situation warranted intervention (fig. 3b). The 2005 black rhino population size estimate of 65 animals in an area of 62 km 2 far exceeded the management level originally set for this sanctuary (KWS 1993), which was also no longer applicable due to the significant degradation of habitat by competing browsers, notably elephants and giraffes. The carrying capacity of the sanctuary had been reduced from an estimated 1-1.5 rhino/km 2 (Goddard 1969; 1970) to approximately 0.6 rhino/km 2 (Brett and Adcock 2002; Okita-Ouma 2004). The average body condition of both rhinos and elephants had also deteriorated from an average ‘good’ to ‘fair’ - ‘poor’ (Okita-Ouma and Wandera 2006).

The overstocking was threatening the sanctuary’s productive potential for rhino, as well as their nutrition, condition and health. The browser impact had caused ever-accelerating rates of decline in browse and predictions showed very low levels of browse resources by 2007. In such a situation, adverse or drought conditions could potentially irreversibly damage the future productivity of the area and cause a cessation of breeding by the rhino population as well as a population crash. In similar situations, other black rhino populations have crashed (Hitchins 1968; Emslie 1999; Emslie 2001).

The high number of large herbivores also imposed a major burden on the sanctuary’s infrastructure, especially the piped water supply. The piped water resources (and security) within the fenced area have been a major attraction for elephants in particular, and presumably encouraged animals to remain resident and breed within the sanctuary area. The 15 km of reticulation and three waterholes provides the only source of water in the sanctuary during the dry season (July – October). With the increasing densities of herbivores came dangerous water access confl icts that developed between the rhinos and elephants. There were significant maintenance problems and costs associated with elephants digging up and breaking water pipes and fittings. Monitoring rhino also become a hazardous exercise.

Le Sanctuaire de rhinocéros de Ngulia (clôturé) qui se trouve au Parc National de Tsavo West, au Kenya, était parmi les sanctuaires de rhinocéros qui réussissait le mieux à élever des rhinocéros noirs depuis sa création en 1986 jusqu’en 2001 quand le taux de croissance du rhinocéros noir a commencé à décliner. Ce déclin était principalement imputable à la dégradation de l’habitat et à la réduction des plantes à brouter qui constituent la nourriture des rhinocéros noirs. Cette dégradation de l’habitat était causée par une forte densité d’éléphants et d’autres herbivores concurrents dans le sanctuaire. Les plantes constituant la nourriture des rhinocéros noirs se sont réduites de 59% ce qui a réduit considérablement la capacité de charge pouvant assurer la productivité maximale des rhinocéros noirs dans le sanctuaire. Pour renverser la situation, le Service de la Faune du Kenya a élargi le sanctuaire de 62km 2 à 88km 2 et entre 2005 et 2006, il a fait la translocation de 255 éléphants hors du sanctuaire jusqu’à environ 15km de la ligne de clôture du sanctuaire en laissant au moins deux éléphants. La translocation a été faite en trois phases en utilisant trois stratégies différentes. La première phase a consisté à chasser les familles d’éléphants du sanctuaire par l’usage des hélicoptères. Dans la deuxième phase, les éléphants mâles adultes matures étaient chimiquement immobilisés et transférés, alors que la troisième phase consistait à l’immobilisation chimique et à la translocation de familles d’éléphants. Cette troisième phase (et technique) était la plus réussie avec une moyenne de 15 éléphants transférés par jour. Il y a eu deux cas d’éléphants qui ont pu revenir au cours de l’exercice de translocation. On s’attend à ce que la végétation et le brout disponible pour les rhinocéros s’améliorent et par conséquent contribuent à restaurer la croissance optimale de la population du rhinocéros noir.