 Tragelaphus
buxtoni
Mountain nyala |
Taxonomy | Description
| Reproduction | Ecology
| Behavior | Distribution
| Conservation | Remarks
| Literature |
| Taxonomy
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Tragelaphus buxtoni [Lydekker, 1910].
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Citation: Nature (London), 84:397.
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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). Due
to its 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).
General Characteristics
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).
Reported measurements for mountain nyala (Tragelaphus buxtoni) |
| Source |
Adult Weight |
Head & Body Length |
Shoulder Height
|
Tail Length |
| Alden et al., 1995 |
150-250 kg |
190-250 cm |
90-135 cm |
20-25 cm |
| Brown, 1969a |
180-225 kg  |
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- |
- |
| Kingdon, 1997 |
180-300 kg
150-200 kg  |
240-260 cm
190-200 cm |
120-135 cm
90-100 cm |
20-25 cm |
| Nowak, 1991 |
200-225 kg |
190-260 cm |
90-135 cm |
- |
| Walther, 1990 |
180-300 kg
150-200 kg |
240-260 cm
190-220 cm |
120-135 cm
90-110 cm |
20-25 cm |
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).
Ontogeny and Reproduction
Mating appears to peak during December and January, the dryest time of year
(Brown, 1969a; Kingdon, 1997). However, this may be regional as peaks
in births vary with location, a feature likely due to climate differences
(Brown, 1969a). In Bale, the majority of births appear to occur in
April, May and June, while 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 (Kingdon, 1997). Once sure on their feet, the
young will join their mother, and will remain closely attached to her for
as long as two years, by which point the young females are pregnant and males
have long horns and leave to join a bachelor herd (Kingdon, 1997). It
appears that a female may not breed again as long as her previous offspring
is still with her (Brown, 1969b).
Ecology
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 (Brown, 1969a;
Kingdon, 1997). Giant heath (Erica arborea) 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). These groupings are
primarily composed of females and their young, but in about half of observed
cases a mature (but not old) bull will be present (Brown, 1969b; Kingdon,
1997). Kingdon (1997) suggests that these aggregations are temporary
associations of different females. 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.
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). 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 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).
Behavior
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).
Little is known about the mating activity of this species. Older males
display by walking in slow circles with their dorsal crest raised and head
held high (Kingdon, 1997). Once one male drops his head, the engagement
is broken off and the subordinate departs (Kingdon, 1997).
Distribution
The mountain nyala is limited in its distribution to the Bale massif
(mountain range) in the Arussi and Bale Provinces of Ethiopia (Brown, 1969b;
Kingdon, 1997). 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 (IUCN, 2002).
Range Map (Compiled from Kingdon, 1997; IAE, 1998)
Conservation Status
The mountain nyala is listed as endangered (A1a, C1) by the IUCN (2002),
and is not listed by CITES. 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; these
authors counted a maximum of 732 individuals in Bale National
Park. 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).
Remarks
The mountain nyala was brought to the attention of Western science by Lydekker
in 1910, who suggested that this species "in some degree intermediate between
the Nyala (Tragelaphus angasii) and the Kudu (Strepsiceros
capensis) . . . 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).
Tragos (Greek) a he-goat;.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).
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Local names (from Brown, 1969a; Kingdon, 1997)
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Azagen [Ethiopian dialect]
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Gedemsa [? - occasionally used in English; also the name of an Ethiopian
volcano]
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French
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Nyala des montagnes (Walther, 1990)
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German
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Bergnyala, Mittelkudu (Walther, 1990)
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Spanish
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Niala de montaña
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Literature
Cited
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Brown, L. 1969a. Ethiopia's elusive nyala. Animals 12:
340-344.
Brown, L. H. 1969b. Observations on the status, habitat, and behaviour
of the mountain nyala Tragelaphus buxtoni in Ethiopia. Mammalia
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East, R. [compiler]. 1999. African Antelope Database 1998. IUCN/SSC Antelope
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IEA (Institute of Applied Ecology) 1998. Tragelaphus buxtoni.
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Refera, B., and A. Bekele. 2004. Population status and structure
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Additional Resources
Burton & Pearson. 1987. Rare Mammals of the World. Stephen Greene Press,
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Dorst, J., and P. Dandelot. 1970. A Field Guide to the Larger
Mammals of Africa. London: Collins.
Haltenorth, T., and H. Diller. 1980. The Collins Field Guide
to the Mammals of Africa including Madagascar. Lexington, MA: The Stephen
Greene Press.
Hillman, J.C. 1986. Conservation in Bale Mountains National Park, Ethiopia.
Oryx 20:89.
*Oboussier, H. 1978. Notes on the mountain nyala Tragelaphus
buxtoni and bongo Taurotragus euryceros: A comparison of body
and brain structure. Zeitschrift fuer Saeugetierkunde; 43(2): 114-125.
Stephens, P. A., d'Sa, C. A., Z. C. Sillero, W. N. Leader. 2001.
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Stuart, C., and T. Stuart. 1996. Africa's Vanishing Wildlife.
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Woldegebriel, G. K. 1996. The status of mountain nyala
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Yalden, D. W., and M. J. Largen. 1992. The endemic mammals of
Ethiopia. Mammal Review 22(3/4): 115-150.
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