thumb|juvenile
thumb|young male
The mountain nyala (Amharic: የደጋ አጋዘን) (Tragelaphus buxtoni) or balbok, is a large antelope found in high altitude woodlands in a small part of central Ethiopia. It is a monotypic species (without any identified subspecies) first described by English naturalist Richard Lydekker in 1910. The males are typically tall while females stand at the shoulder. Males weigh and females weigh . The coat is grey to brown, marked with two to five poorly defined white strips extending from the back to the underside, and a row of six to ten white spots. White markings are present on the face, throat and legs as well. Males have a short dark erect crest, about high, running along the middle of the back. Only males possess horns.
The mountain nyala are shy and elusive towards human beings. Four to five individuals may congregate for short intervals of time to form small herds. Males are not territorial. Primarily a browser, the mountain nyala may switch to grazing occasionally. Females start mating at two years of age, and males too become sexually mature by that time. Gestation lasts for eight to nine months, after which a single calf is born. The lifespan of a mountain nyala is around 15 to 20 years.
The typical habitat for the mountain nyala is composed of montane woodlands at an altitude of . Human settlement and large livestock population have forced the animal to occupy heath forests at an altitude of above . Mountain nyala are endemic to the Ethiopian Highlands east of the Rift Valley, between 6°N and 10°N. Up to half of the total population of the mountain nyala occurs in the area of Gaysay, in the northern part of the Bale Mountains National Park. The mountain nyala has been classified under the Endangered category of the International Union for Conservation of Nature and Natural Resources (IUCN). Their influence on Ethiopian culture is notable, with the mountain nyala being featured on the obverse of Ethiopian ten cents coins.
Taxonomy
The mountain nyala was first described by English naturalist Richard Lydekker in 1910. Its scientific name is Tragelaphus buxtoni. The species has been classified under the genus Tragelaphus of the family Bovidae. The mountain nyala was first brought to England in 1908 by Major Ivor Buxton, after whom the species has been named. Major Buxton, who had returned from a hunting trip in Ethiopia, first presented a specimen he had shot to British taxidermist Rowland Ward, who later on notified Lydekker about the discovery. It was the last large antelope to be discovered in Africa. The spiral horns and white markings on the face and across the flanks established it as a species of Tragelaphus. Lydekker believed that the species was related more closely to the nyala (T. angasii) than to the two kudu species (then placed under the genus Strepsiceros). In fact, mountain nyala's similarity to both Tragelaphus and Strepsiceros led to the merger of the latter into the former genus.
In 2005, Sandi Willows-Munro of the University of KwaZulu-Natal (Durban) carried out a mitochondrial analysis of the nine Tragelaphus species. mtDNA and nDNA data were compared. The results showed that the mountain nyala is sister taxon to bushbuck (T. scriptus), sitatunga (T. spekii) and bongo (T. eurycerus) in the mitochondrial tree (phylogenetic relationships obtained using mitochondrial data). However, in the nuclear tree, bushbuck, mountain nyala and sitatunga plus the bongo are three equal branches. Hence the mountain nyala forms a monophyletic clade with these three species. The greater kudu clade split from the clade formed by mountain nyala, bongo, sitatunga and bushbuck approximately 8.6 million years ago.
Description
The mountain nyala is a large sexually dimorphic bovid. The head-and-body length is approximately in males and in females. The males are typically tall while females stand at the shoulder. Males weigh and females weigh . The bushy tail reaches the heel, and is long.
The mountain nyala resembles the greater kudu in that both have an array of white spots along their flanks and possess spiral horns. However, the greater kudu can be told apart from the mountain nyala due to the former's greater height and paler colour. Moreover, the horns in greater kudu have two to three spirals, and the tips are farther apart. Another species similar to the mountain nyala is the nyala, but the latter can be easily distinguished from the former due to its smaller size and a fringe of long hair along its throat and neck. The horns of nyala, though very similar, are slender and narrower.
Four to five individuals may congregate for short intervals of time to form small herds. However, groups containing as many as 100 individuals have been reported from the Bale Zone, composed of several family units moving in and out periodically. Size and longevity of such large herds depends upon the season, habitat type and the time of the day. Female and juvenile groups have adult females accompanied by a calf of her previous year and another of the current year. These groups are led by adult males, depending on the presence of oestrus. Bachelor herds are formed by non-dominant adult bulls and young males, consisting of up to 13 individuals. Mixed sex groups may also be formed. Old bulls tend to lead a solitary life, though they may occasionally visit female herds looking for females in oestrus. Dominance hierarchies are observed in both sexes.
Males are not territorial, and have home ranges covering in the wet season. Females and juveniles, on the other hand, occupy much smaller ranges of about in the wet season. Dry season ranges are much larger than the wet season ones for both sexes. Males often wrestle using their horns.
Nowadays the continuous blocks of woodland habitat have been reduced to a series of pockets, interspersed in large cultivated lands. Human settlement and large livestock population have forced the animal to occupy heath forests at an altitude of above rich in Erica arborea, Erica trimera, Hypericum, Euphorbia, and Helichrysum species. They may even be forced into afroalpine grasslands containing Alchemilla and Festuca species, at an altitude of up to . In the eastern borders of its range, the mountain nyala has usually been observed to occupy areas at lower altitudes of about . A study identified an area of on the southern escarpment of the Bale Mountains as the most sustainable habitat for the mountain nyala.
Threats and conservation
thumb|Taxidermied specimens at the [[American Museum of Natural History]]
Major threats to the survival of the mountain nyala include illegal hunting, habitat destruction, encroachment by livestock, predation of calves by dogs, expansion of montane cultivation and construction at high altitudes. The animal is extensively hunted for its horns and meat. The meat is utilised in local medicine and for making nipples for traditional milk bottles. Impact of trophy hunting programs is obscure, and current trophy hunting quotas may be unsustainable in the long term although, if well regulated, trophy hunting could play an important role in the long term management of this species. After the Bale Mountains National Park, the small Kuni-Muktar Mountain Nyala Sanctuary was established in 1990 was established as a second protected area. But by 1996 the sanctuary had been so severely affected by deforestation, poaching, cultivation and gully erosion, that the populations soon disappeared from there.
Mountain nyala are hunted by humans, for instance, by the Oromo people. The Oromo do not hunt these animals in general, except for a day close to Easter, when all able-bodied men set out on horses for a hunt.