Mountain Nyala
Population estimates
The first studies undertaken on the mountain nyala focused primarily on the species’s status and distribution. Following surveys in 1966, L.H. Brown estimated between 4000-4500 mountain nyala across the Bale Mountains with total numbers across Bale and Arsi perhaps as high as 7000-8000 in the 1960s (Brown 1969, 1971). Brown’s estimate and subsequent ones are mostly speculative as no systematic or comparable data have been collected over the years and counts have been restricted to only small parts of the species range. Nevertheless, it is widely alleged that mountain nyala have declined in number and range over the last several decades. In 1969, C. Buer estimated no more than 2000 animals in the Bale Mountains and reiterated previous concerns of uncontrolled hunting and habitat destruction (Buer 1971). Hillman (1986) suggested an overall population of 1250-1400 in Bale, with 1,100 animals in the Gaysay Valley alone. Political upheaval in the early 1990s and associated illegal poaching and livestock encroachment in the park had a dramatic effect on the mountain nyala population. Estimates made by the park in 1994 put the population at around 350-560 animals with only 150-260 animals in the Gaysay Valley and fenced area around the park headquarters (Woldegebriel 1997). There have been signs of recovery since, with estimates of 550-1000 in Gaysay and the park headquarters using line transects (Stephens et al. 1997). More recently, the population in Gaysay and the park headquarters was estimated at 669 based on total counts (Refera and Bekele, 2004). Couple with ad hoc sightings elsewhere in the park, a total BMNP population of 704 animals was suggested at the time. Between 2002-2005 the Gaysay Valley and park headquarters population was estimated between 887 and 965 (95% CI) animals based on Distance sampling and total counts (Mamo 2007) and 677 individuals based on total counts conducted in 2007 (A Atickem, unpublished data). The mountain nyala population in the Gaysay Valley and park headquarters are relatively easier to observe and, thus monitor. Coupled with their close proximity to the park, it is also the best studied population. However, it is now well recognized that a large mountain nyala population is located in the eastern side of the BMNP in three hunting concessions (Besmena Odo Bulu, Abasheba Demmaro and Shedem Berbere) which together represent over 1000 km2 of suitable mountain nyala habitat and may contain as many as 500 mountain nyala (Evangelista 2006, Malcolm and Evangelista 2004). Between 2000 and 2003, Malcolm and Evangelista (2005) conducted a rapid assessment of the known range and status of the mountain nyala in Ethiopia and, coupled with historic accounts and other reports, suggested a total population of 3500-4000 individuals with 2500-3000 mountain nyala in the Bale Mountains (including the park and adjacent areas). Later estimates suggest that population numbers may be even higher (Evangelista 2006, Evangelista et al 2007) All regional population estimates remain tentative as they are mostly based on brief observations and second-hand reports rather than any systematic sampling. Even where total count, line transect or point counts have been employed, estimates remain uncertain given the suite of assumptions inherent in these methods, difficulty observing animals in the dense vegetation and rugged terrain across most of the species’ range, and lack of comparable methods employed. This situation, coupled with the species’ elusive nature, has resulted in a high degree of uncertainty regarding the status of mountain nyala in the Bale Mountains and elsewhere in Ethiopia, as well as lack of data with which to assess population trends.
Behavioural ecology
Richard Lydekker wrote several descriptive papers on mountain nyala shortly after its initial discovery in 1908, but the species remained almost entirely unknown to the scientific community until Leslie Brown travelled to Ethiopia in the early 1960s and wrote several accounts on the species. The few scientific studies conducted since then have mostly been conducted in the Gaysay Valley at the northern extreme of the BMNP. L. Brown and, later studies undertaken by C. Hillman provided the first detailed description of the species behavioural ecology, including its social structure, breeding behaviour, feeding behaviour, habitat associations, and some provisional notes on predation. Later research conducted by Befekadu Refera between 2001-2001 as part of his MSc at the University of Addis Ababa and Yoseph Mamo between 2003-2005 as part of his PhD at the University of Aberdeen examined various aspects relating to the sex and age structure of the population, habitat use, activity patterns, and the impact of local people and livestock on mountain nyala habitat availability. A comprehensive review of the current state of knowledge on the mountain nyala, including population status, habitat availability, behavioural ecology and conservation threats has been compiled by Evangelista et al. (2007).
Additional research is now being undertaken by Anagaw Atickem towards his PhD at the University of Addis Ababa (in collaboration with the University of Oslo). His study examines the effects of habitat fragmentation and trophy hunting on mountain nyala. A detailed analysis of population demography and population connectivity within and around the BMNP will be undertaken using field observations and molecular genetic tools. Microsatellite DNA analysis is also being used to measure the levels of genetic variability within and between the disjunct populations in the Bale Mountains as well as dispersal and gene flow between them. The distribution of suitable mountain nyala habitat and land use patterns within the Bale Mountains will be assessed using satellite images and remote sensing data. Together, these data will be used to assess the impact of habitat loss, fragmentation, and sport hunting on the population status and conservation of mountain nyala. When sustainably implemented, mountain nyala sport hunting has the potential to provide economic incentives for conservation as well as benefits to local communities. This research will contribute establishing sustainable harvest levels and devising appropriate conservation and management strategies for the species.
Disease
A brief epidemiological study was also carried out to assess the prevalence and risk of disease transmission between mountain nyala and domestic ungulates in the BMNP. Parasite prevalence was assessed in cattle, sheep, and mountain nyala. Parasites were present all ungulate faecal samples tested and included Fasciola, Paramphistomum, Trichuris and Moniezia species. In addition, Echinococus granulosus cysts, F. hepatica, Bunostomum trigonocephalum, M. expansa, T. ovis, Oesophagostomum columbianum, Dictyocaulus filaria, Trichostrongylus colubriformis,Haemonchus contortus, Chabertia ovna and Avitellina centripunctata were recovered from postmortem analysis of four sheep bought from villages near the park. All sheep serum samples were negative for peste des petites ruminants antibodies, whereas 3.2 % cattle serum samples were positive for contagious bovinepleuropneumonia and 10.2 % of serum samples were positive for rinderpest. Seven mountain nyala (and two Menelik’s bushbuck) tested for rinderpest, pest des petites ruminants and contagious bovinepleuropneumonia antibodies were negative.
This research was conducted by Dr. Fekadu Shiferaw from the Wildlife Conservation Department and the National Animal Health Research Center in collaboration with EIAR with funding from the Welcome Trust (UK).