Tragelaphus buxtoni [Lydekker, 1910].

Citation: Nature (London), 84:397.

Type locality: Ethiopia, Bak Prov., Sahatu Mtns, southeast of Lake Zwai, 9,000 ft. (2,743 m).

The taxonomic record (above) is taken from Wilson and Reeder (1993). With a small native range and recent discovery, the taxonomy of this species is uncomplicated. There are no recognized subspecies, nor are there any synonyms (Wilson & Reeder, 1993). The mountain nyala is placed in the subgenus Tragelaphus [De Blainville, 1816] (Nowak, 1991).

Mountain nyala males are much larger than females, a character typical of the spiral-horned antelopes (Brown, 1969a; Nowak, 1991). Few morphometric studies have been conducted on this species, with the result that measurements reported in the literature are nearly identical (likely recycled from previous publications). Typical body measurements are given by Alden et al. (1995). Evangelista, Swartzinski, and Waltermire (2007) report that males living in forest habitats may be much larger than those from alpine/heath habitats (240-32 kg vs. 180-250 kg respectively).

The coat of T. buxtoni is smooth and glossy during the summer, becoming shaggy during the cooler, damper winter months (Kingdon, 1997). The general color is a greyish chestnut or sandy grey-brown, although there is considerable variation between individuals (Nowak, 1991; Alden et al., 1995). Old bulls are a dark brownish-grey overall, and are readily distinguished from younger males, which have more brown and less grey in their pelage (Brown, 1969a). Young females are reddish brown, growing browner and subsequently greyer with age, although never darkening to the extent of males (Brown, 1969a). The age of young females can be visually estimated until they have darkened in color, after which accurately assessing age is difficult (Brown, 1969b). Males are always darker than females of the same age (Brown, 1969a).

The undersides are paler than the back, and the dark legs are accentuated by white patches (Alden et al., 1995; Kingdon, 1997). Typical of the genus Tragelaphus there is a scatter of spots and 2-5 poorly defined vertical stripes on the back and flanks (Alden et al., 1995; Kingdon, 1997). Females are more inclined to have white side-stripes than the males, as in other members of the genus Tragelaphus (Brown, 1969a; Kingdon, 1997). The bushy tail is white on the underside (Lydekker, 1911). Facial markings consist of two white spots which form (or almost form) a chevron between the eyes, and two white cheek spots (Walther, 1990; Nowak, 1991). The chin is often white, and there is a deep gorget of white on the throat and a much wider white crescent on the chest (Lydekker, 1911; Alden et al., 1995). The dark color of the males increases contrast of white markings, which may function as signals in display (Brown, 1969b; Kingdon, 1997). Males also possess a white dorsal crest, which extends from neck to base of tail, and a mane of shaggy brown hair on the neck (Brown, 1969a; Walther, 1990; Kingdon, 1997).

Only males possess the lyrate horns typical of the spiral-horned antelopes (Brown, 1969a). There are usually one and a half to two spiralling coils, and two longitudinal keels which run along the horn (Walther, 1990). There is considerable variation in the tightness of the horn spiral, horn thickness, and length (Kingdon, 1997). The horns are generally a dark brown or greyish color, but the tips are yellow, a feature which may emphasize the length of the horns to conspecifics (Lydekker, 1911). Horn length may vary from 85 cm to 118.7 cm - the record horn length - along the outer curve (Nowak, 1991; Alden et al., 1995). The type specimen, collected by Mr. Ivor Buxton in 1908, had horns 94 cm long (as measured along the outer curve), with a basal girth of 23.5 cm, and a tip-to-tip interval of 53.3 cm (Lydekker, 1911).

Breeding may occur throughout the year, although a peak in mating occurs during December and January, the driest time of year (Brown, 1969a; Kingdon, 1997). However, this may be regional: peaks in births vary with location, a feature likely due to climate differences (Brown, 1969a). In Bale, Brown (1969b) reports that the majority of births occur in April, May and June, although Evangelista, Swartzinski, and Waltermire (2007) put the peak in August and September. In Arussi observations suggest it may be from October to December (Brown, 1969b). Calves observed are often of variable sizes, indicating that a wide birthing season is present (Brown, 1969b). Despite the presence of two pairs of mammae, there is only a single young born after the 8-9 month gestation (Nowak, 1991; Kingdon, 1997). Young are born ochre-colored - considerably lighter than the grey-brown adults - and darken with age (Kingdon, 1997).

Calves lie up for a few weeks in dense cover, reducing the risk of predation in more open country. Once sure on their feet, the young will join their mother, continuing to nurse until 3-4 months of age (Evangelista, Swartzinski, and Waltermire, 2007). Calves remain closely attached to their mothers for as long as two years (Evangelista, Swartzinski, and Waltermire, 2007). Females reach sexual maturity between two and three years of age; males may be capable of siring offspring at this time as well, but are not able to successfully compete for breeding opportunities until five to eight years of age (Kingdon, 1997; Evangelista, Swartzinski, and Waltermire, 2007). Horns begin growing in males at six months of age, and are of adult size by six years of age (Evangelista, Swartzinski, and Waltermire, 2007). It appears that a female may not breed again as long as her previous offspring is still with her (Brown, 1969b).

Typical habitat utilized by T. buxtoni is a mosaic of high-altitude woodland, bush, heath, moorland, and valley-bottom grassland, including species such as Alchemilla, giant lobelia, and giant heath (Erica arborea) (Brown, 1969a; Kingdon, 1997). Giant heath forests are used for cover year-round, while juniper and Hagenia woodlands and brush (containing sagebrush, Artemesia, and Helichrysum) provide refuge during the dry season (Brown, 1969a; Brown, 1969b; Kingdon, 1997). Local observers have referred to the mountain nyala as a forest animal (Brown, 1969b). True to their name, mountain nyala are rarely found below 2,000 meters above sea level, and may inhabit altitudes as high as 4,000 meters (Brown, 1969a).

T. buxtoni travels in small groups of 2-13 animals, with an average of 4 and 6 individuals in a herd (Brown, 1969a). Group size tends to be larger in open habitats than in forests (Evangelista, Swartzinski, and Waltermire, 2007). These groupings are primarily composed of females (including one matriarch) and their young, but in about half of observed cases a mature (but not old) bull will be present (Brown, 1969b; Kingdon, 1997; Evangelista, Swartzinski, and Waltermire, 2007). Herds larger than 13 individuals are occasionally reported (Brown, 1969a). Young males older than two years of age are somewhat gregarious, living in herds with a hierarchy determined by frequent horn-wrestling contests (Kingdon, 1997). Mature males may associate in small groups of between two and seven individuals (Brown, 1969b). Old males are usually solitary, while solitary females are exceptionally rare (Brown, 1969a; Brown, 1969b; Kingdon, 1997). The population appears to be skewed towards females (accounting for 65% of observations, not including obvious calves) (Brown, 1969a); recent surveys have found a similar 1:2.5 ratio of adult males : adult females (71% females) (Refera and Bekele, 2004). In the Bale Mountains, one in four females was accompanied by a calf at any given time (Brown, 1969a).

Groups tend to be smaller during dry season, when they range widely (Kingdon, 1997; Refera and Bekele, 2004). During the rains, females restrict their movements to an area about 5 km², while males may range as widely as 20 km² (Kingdon, 1997). Generally sedentary, do not appear to be territorial (Walther, 1990). Mountain nyala likely make seasonal migrations up- and down-hill: seeking the shelter of the low-altitude forests during the rains, when the high mountains become very inclement (Brown, 1969a). Coincidentally, there is increased availability of lower altitude grasslands during the rains (Kingdon, 1997).

Local population densities may vary widely - Brown (1969a) found an average of 2.7 animals per square kilometer, although values ranged from nothing to 10.8 animals per square kilometer. Kingdon (1997) reports that T. buxtoni may reach densities as high as 20 individuals per square kilometer in Bale Mountain National Park, while Brown (1969b) suggested that local densities in favorable habitat might be as high as 40 animals per square kilometer. Their high local density and habituation to humans makes viewing mountain nyala around the Bale Mountain National Park headquarters (just outside of Dinsho) extremely easy.

Potential predators of the mountain nyala include leopard (Panthera pardus), spotted hyena (Crocuta crocuta), and lion (Panthera leo), although the latter two are rarely found at the altitudes frequented by T. buxtoni (Brown, 1969b). Leopards are most likely to kill young animals, as adults are larger than a leopard would normally attack, but due to the abundance of other, smaller prey, the number of mountain nyala taken by this species is likely low (Brown, 1969b). Smaller predators such as serval (Leptailurus serval) and jackals (Canis adustus) may kill the occasional calf, but are likely not a major threat (Brown, 1969b).

The staple of the mountain nyala's diet are herbs and shrubs, although grasses, ferns, and lichens are also eaten (Kingdon, 1997). Among the most frequently browsed plants are the Solanaceae (tomato family), St. John's wort (Hypericum), lady's mantle (Alchemilla), and goosegrass (Galium) (Kingdon, 1997); forest grasses eaten include Koeleria, Agrostis, and Poa (Brown, 1969b). Evangelista, Swartzinski, and Waltermire (2007) provide a full list of recorded plant species in the diet of T. buxtoni. At high altitudes, leaves of giant lobelia are eaten, a habit which has been used in censusing populations (Brown, 1969a). Although often assumed to be a browser, Brown (1969) found that T. buxtoni consumes considerable amounts of grass at lower altitudes, such as when sheltered in giant heath forests. Annual burns in the Ethiopian highlands produce fields of fresh shoots which are preferred by T. buxtoni (Brown, 1969a). During the dry season they may feed on fallen leaves of Hagenia (rosewood), while during the rains, when sedge grasslands become waterlogged, this species may eat water plants (Kingdon, 1997). Despite the prevalence of Alchemilla johnstoni and Erica arborea in mountain nyala habitat, these species are rarely eaten (Brown, 1969b). T. buxtoni was never observed drinking by Brown (1969b), and, although locals have stated that they may do so frequently at night, no evidence to support this was found. Due to the high moisture content of the plants in the Ethiopian mountains, sufficient moisture is probably gathered by eating (Brown, 1969b).

According to Brown (1969a; 1969b) mountain nyala are most active from 1600 hours to 0800 hours, the late afternoon, night, and early morning. Adult males appear to have shorter active periods, rising two hours before dark and seldom being seen after the early hours of the morning (Brown, 1969b). However, in undisturbed areas, foraging may occur at at any hour of the day (Brown, 1969a). In addition to human disturbance, grazing in the open is also impacted significantly by the weather - mountain nyala remain in dense cover when it is either sunny and dry or cold and raining (Brown, 1969a). Feeding bouts of about 30 minutes are often separated by periods when the animals seek cover (Brown, 1969a).

Emerging from cover in the late afternoon, T. buxtoni shows extreme caution - one bull was observed to stand stock-still for twenty minutes, likely looking for danger, before moving into a patch of heath (Brown, 1969b). Herds are generally difficult to approach (Brown, 1969a). When a group lies down to rest, they often choose a hollow along a ridge, from which they can flee should a predator come into view over the skyline (Brown, 1969a). Additionally, individuals will orient themselves so as to have all directions observed by a member of the herd (Brown, 1969b). However, when feeding, mountain nyala walk unconcernedly with heads down and tails swinging from side to side, at which point they are easy to approach (Brown, 1969b). Humans appear to have better eyesight in in low-light conditions than T. buxtoni (Brown, 1969b).

T. buxtoni is generally silent (Brown, 1969b). Females are more likely to vocalize than males, with two main calls being recognized: the first, a throaty, hoarse cough or grunt, is made when the danger is neither serious or immediate; the second vocalization, a clear low bark (described as a "buh") is made the cause of the alarm is apparent (Brown, 1969a; Brown, 1969b). In a mixed herd situation, a single female, likely the leader, gives the alarm (Brown, 1969b). When alarmed, female mountain nyala move with a "pecking" gait while holding their heads high (Brown, 1969b). When in full flight, the white underside of the tail is exposed and hidden repeatedly, producing a signal easily seen in dense brush or low light conditions (Brown, 1969b). If startled, a herd will often fragment and act confused (Brown, 1969b). Males are usually silent, even when alarmed, although they may bark in challenge to other males or when approaching a female herd (Brown, 1969a). Old males have been found lying still in long heath, bolting only when discovered at close range (Brown, 1969a) - indeed, I was able to approach within a few meters of one resting male in the Gaysay Valley before he stood up and, after watching me for several seconds, took flight.

Dominance among males is determined largely through ritualized posturing (Evangelista, Swartzinski, and Waltermire, 2007). Kingdon (1997) reports that males display by walking in slow circles with their dorsal crest raised and head held high, although I witnessed one male (in February 2010, Bale Mountains National Park headquarters) challenging another with dorsal crest flared and head stretched forward and downwards, as described by Evangelista, Swartzinski, and Waltermire (2007). This male held his ears out and tilted forward at a peculiar angle. According to Kingdon (1997), the challenge is broken off when the subordinate drops his head and departs. Physical fights between males are uncommon, but are intense when they do occur, with rival males clashing horns, trying to make the opponent lose their balance (Evangelista, Swartzinski, and Waltermire, 2007). "Object-horning", in which a male thrashes at vegetation or the ground, is common and may serve to "intimidate other males ... or advertise fitness to females" (Evangelista, Swartzinski, and Waltermire, 2007).

The mountain nyala is limited in its distribution to the Arussi and Bale massifs (mountain ranges) in the province of Oromia in Ethiopia (Evangelista, Swartzinski, and Waltermire, 2007). It was estimated by Brown (1969b) that the total area of potential habitat was 5,200 square kilometers, although due to human disturbance this area is likely less than 3,900 square kilometers. They are present at altitudes of 3,000 to 4,200 meters, although they may rarely be found as low as 1,800 meters (Kingdon, 1997).

Countries: Ethiopia (Sillero-Zubiri, 2008).

The mountain nyala is listed as endangered (Criteria A1a, C1) by the IUCN (Sillero-Zubiri, 2008), and is not listed by CITES (2009). In the 1970's, the number of mountain nyala was around 1,000 animals. A major increase occurred in the 1980's - the total population was estimated at 2,000 to 4,000 individuals in 1988, at least half of which were restricted to a specific region of Bale Mountain National Park (Kingdon, 1997). East (1999) reports an estimate of about 2,500 individuals, while Refera and Bekele (2004) give a much more pessimistic estimate of 1000 animals throughout Ethiopia. Evangelista, Swartzinski, and Waltermire (2007) argue that these estimates are severely low (based on incomplete range data), and conclude that the total population likely exceeds 4,000 animals. T. buxtoni numbers appear to fluctuate: East (1999) suggests that numbers are increasing within Bale National Park, while Refera and Bekele (2004) suggest they may still be in decline.

The principal threat to survival is a reduction in range due to human encroachment. The resulting disturbances, involving the occupation of suitable areas by livestock and the constant passage of people through the habitat, continues to be detrimental (Brown, 1969a; Brown 1969b; Refera and Bekele, 2004).

The mountain nyala was brought to the attention of Western science by Lydekker in 1910, who suggested that this species was "in some degree intermediate between the Nyala (Tragelaphus angasii) and the Kudu (Strepsiceros capensis) ... [and] might be known as the Spotted Kudu" (Lydekker, 1911). The original scientific name proposed was Strepsiceros buxtoni, allying this species with the greater kudu (Lydekker, 1911). However, upon further examination, Lydekker changed his mind, switching the genus to Tragelaphus indicating an affinity with the nyala of southern Africa (Lydekker, 1911; Shuker, 1993). Finally, due to strong similarities between the mountain nyala and member of both the genus Strepsiceros and the genus Tragelaphus, it was proposed that the two genera be merged, removing Lydekker's dilemma (Lydekker, 1911).

'Nyala' (pronounced "n'YAH-la") is the Swahili name for Tragelaphus angasii, a relative of this antelope. Despite this association, the mountain nyala is now thought to be more like a kudu in its nature (Shuker, 1993).

Tragelaphus is derived from tragos (Greek) a he-goat and elaphos (Greek) a deer; in combination referring to an antelope. The first specimen of this large spiral-horned antelope was procured by Mr. Ivor Buxton in 1908, after whom the specific name is titled (Lydekker, 1911).

Local names

("Ye Dega Agazen") [Amharigna]

Gadamsa [Oromifa]

 

French

Nyala des montagnes (Walther, 1990)

 

German

Bergnyala, Mittelkudu (Walther, 1990)