http://journals.cambridge.org Downloaded: 29 May 2014 IP address: 2.124.94.157 Population and habitat assessment of the Critically Endangered hirola Beatragus hunteri in Tsavo East National Park, Kenya J AMES P ROBERT ,B EN E VANS ,S AM A NDANJE ,R ICHARD K OCK and R AJAN A MIN Abstract The Critically Endangered hirola Beatragus hun- teri exists in two populations, a natural population on the Kenyan–Somali border and a translocated population in Tsavo East National Park, Kenya. The Tsavo population is becoming increasingly important for the survival of the hirola yet its status is unknown and little is understood about the factors that limit its growth. Here we report the size, distribution and demographic parameters of the Tsavo population of hirola and consider whether insufficient suitable habitat could be limiting its growth. The Tsavo population has not increased since 2000, when the last census was carried out, but neither has it significantly decreased. The importance of habitat as a limiting factor is dependent on the hirola’s ability to utilize marginal habitat. Keywords Aerial survey, Beatragus hunteri, Critically Endangered, habitat suitability, hirola, Kenya, Tsavo East National Park, vegetation survey Introduction T he hirola Beatragus hunteri (Sclater, 1889) is the sole extant representative of a long-lasting phylogenetic lineage that originated c. 3.1 million years ago and the present population represents the last relic of a once wide- spread genus (Gentry, 1990; Pitra et al., 1998). Beatragus is now recognized as the most threatened monotypic genus of antelope (IUCN, 2011). The global hirola population declined from 16,000 animals in the late 1970s to an estimated 1,600 animals in 1988 (Ottichilo et al., 1995; Butynski, 1999) and now to an estimated 350–500 animals (Evans, 2011; King et al., 2011; Probert, 2011). There are no hirola in captivity (Butynski, 2000) and its extinction would be the first loss of a mammalian genus in Africa since the evolution of modern man (Gentry, 1990; King et al., 2011). The hirola’s natural range has contracted and now comprises an area of no more than 1,500 km 2 on the Kenyan–Somali border. As insurance against the possible failure of efforts to save the in situ population a translocated population was established in Kenya’s Tsavo East National Park (Fig. 1), with translocations in 1963 and 1996 (Hofmann, 1996; Andanje & Ottichilo, 1999; Butynski, 1999; East, 1999). Since the 1996 translocation the Tsavo population has remained stable and no further efforts have been made to increase it. The factors limiting the size of the population and influencing the distribution of hirola in Tsavo are not well understood. This prevents effective planning of conservation management (Butynski, 2000; Andanje, 2002). The hirola population in Tsavo is currently estimated to be 76 individuals, or c. 15% of the global population (K. Kimitei, pers. comm.). The last census was in 2000 but a severe drought in 2008 and 2009 that affected other ungulate species in the region severely may also have affected the hirola population (Probert, 2011). Methods Ground and aerial surveys The original survey method was based on systematic aerial surveys coordinated with ground surveys to facilitate a comparison of counts and calculation of confidence intervals. However, this had to be modified because mechanical problems and difficulties obtaining aviation fuel prevented the ground and aerial surveys running con- currently. We conducted an intensive ground survey during 6 May–17 June 2011, followed by an aerial survey during 30 June–5 July 2011. The ground survey was carried out in a single vehicle by a team of three researchers and a park ranger. To maximize the likelihood of finding hirola we used data from the Kenya Wildlife Service Hirola Monitoring Programme to identify locations of previous sightings and collected information on recent sightings from safari guides and drivers. On completion of the study the identification sheet we created for drivers and guides was expanded into a hirola identification guide. We conducted daily surveys, during 06.30–10.00 and 15.00–18.00, driving on- and off-road transects through areas where hirola had been reported. We also recorded JAMES PROBERT (Corresponding author) and BEN EVANS Department of Life Sciences, Imperial College London, London, UK E-mail jamesprobert@btinternet.com SAM ANDANJE Ecosystem and Landscape Conservation Department, Kenya Wildlife Service, Nairobi, Kenya RICHARD KOCK Wildlife Diseases, Royal Veterinary College, North Mymms, UK RAJAN AMIN Conservation Programmes, Zoological Society of London, UK Received 6 January 2013. Revision requested 26 February 2013. Accepted 11 June 2013. © 2014 Fauna & Flora International, Oryx, Page 1 of 7 doi:10.1017/S0030605313000902