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

Benson Okita-Ouma, Dominic Mijele, Rajan Amin, Francis Gakuya, David Ndeereh, Isaac Lekolool, Patrick Omondi, Daniel Woodley, Moses Litoroh, Juma Bakari, Richard Kock


The Ngulia rhino sanctuary located in the central part of Tsavo West National Park (NP) is completely fenced within an area of 88 km2 following its expansion from 62 km2 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 km2 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/km2 (Goddard 1969; 1970) to approximately 0.6 rhino/km2 (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 conflicts 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.

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