Nyala

Tragelaphus angasii  (Angas, 1849)

Photo: Doug Lee

IUCN Conservation Status:

Nyala = Lower Risk, conservation dependent (LR/cd).
Mountain nyala = Endangered (EN)

The nyala antelope shows a marked sexual dimorphism in size with a large male and a much smaller female. As a result the male is known as a bull in common with the larger antelope species and the female a ewe in common with the smaller antelopes.  Young males are camouflaged by their colour pattern which resembles that of a female.  This protects them from the aggressive behaviour of the dominant male.

Taxonomy

Classification           

The nyala belongs to the genus Tragelaphus or spiral horned antelope, with the following related species

•    Tragelaphus angasii the nyala
•    T. buxtoni the mountain nyala
•    T. eurycerus the bongo
•    T. spekei the sitatunga
•    T. strepsiceros the greater kudu
•    T. imberbis the lesser kudu
•    T. scriptus the bushbuck
•    T. oryx the eland

Subspecies of nyala are not recognised.

Description

The nyala is a medium sized antelope with a build similar to that of a bushbuck and the face of a kudu.  The bull weighs 92-126 kg, has a shoulder height of 104-121 cm and an apron of exceptionally long hair.  Their pelage colour varies from a light chestnut to a chocolate-brown that darkens with age to a dark greyish-black.  There are 10-14 vertical, parallel, white stripes on the flanks.  Distinctive markings include a horizontal white marking on the muzzle just below the eyes, a white chin, two white dots on the cheeks and a white patch on the lower throat. 

Males have two long manes, the first a dorsal mane stretching from the upper neck, down the spine to the tip of the tail and the second from the chin, down the throat to the chest and stomach.  The golden yellow-brown of the lower legs in adult bulls is unique.  Nyala ewes are much smaller weighing only 54-68 kg and have a shoulder height of 82-106 cm.  They are a bright, chestnut-brown and lack the furry coat of the bull.  Nyala lack the scent-marking pre-orbital glands of most other antelope species.

The closely related mountain nyala of Ethiopia is found 2 740 m above sea level in the Chercher, Arusi, Bale and Amorro mountains, weighs 204-227 kg and has an average shoulder height of 134 cm.  

Comparison to man

Trophy

Only adult bulls have well developed horns.  These are lyre-shaped with two full spirals, are smooth and have distinctive white tips 6-8 cm long.  Horn buds appear after six months and reach a length of 20 cm at 15 months.  The first spiral is complete at two years and Rowland Ward minimum trophy quality is reached after five years. 

Occasionally ewes are found with rudimentary, malformed horns.  These ewes are referred to as red bulls as they grow significantly larger than normal ewes.  A red bull with a mass of 114 kg and a trophy of 32.5” or 83 cm was once recorded in the Imfolozi Game Reserve in KwaZulu-Natal.

Habitat requirement

Abundant shade, cover for refuge and nutritious browse are the essential elements of nyala habitat and are found mainly in thicket, closed woodland, riverine bush and forest. Riverine woodland and floodplains with bushy clumps are preferred.  Tropical conditions with a moist climate provide the most suitable environment.  Studies in Mozambique have shown that a nyala spends 70-90% of its life in thicket.  However, nyala also thrive in marginal habitats such as dry savannah providing that a mosaic of thicket bush clumps exists and that permanent water is available within a maximum radius of 800 m. 

A constant supply of fresh drinking water and a large diversity of browse and broadleaf forb species are essential.  A habitat must contain a minimum of 15% thicket and must be an absolute minimum of 60 ha in size.  The less the thicket component of the habitat, the more nocturnal the nyala become.  The grass layer must consist of short to medium sweet grass species 4-23 cm high.  Nyala cannot survive in areas with a rainfall of <300 mm or at temperatures below -2°C. 

However, they have adapted well to the semi-arid Xerophytic Succulent Valley Bushveld of the eastern and southern Cape that has an annual rainfall of 380-450 mm.  Nyala occupy the same feeding niche as the bushbuck and, if allowed to overpopulate, tend to displace them.  Nyala do not pose a threat to bushbuck if managed at lean stocking densities and, in common with them, are highly sensitive to captive handling and to prolonged droughts.

Distribution

Feeding & Nutrition

Nyala are predominantly active during the day in optimal habitats, but become nocturnal in open, marginal habitats or with increased human interference.  Popular literature generally describes the nyala as a concentrate, selective browser, while scientific research has shown that its dietary behaviour is that of a highly selective, mixed feeder taking in large quantities of grass, forbs and browse.  In common with the impala Aepycerus melampus, the nyala can change from 90% browsing to 70% grazing.  In general, grass contributes 12-30% of the dietary intake.

Important browse species include several Acacia spp, Ziziphus mucronata, Grewia spp, Dichrostachys cinerea, Colophospermum mopanae, Capparis sepiaria, Spirostachys africana, Adansonia digitata and many more.  Fruit, pods and flowers are preferred.  Broadleaf forbs are very important and pieces of fresh tree bark stripped by elephant are consumed.  Only the very soft, green, new growth of grass tufts is eaten and dry grass leaves and stems are totally avoided.  Different nyala groups are often seen together at the same locality when sharing a good fodder source.  These groups temporarily tolerate each others’ presence and display little aggression.

Nyala are dependent on fresh water and drink an average of 3.5 litres a day.  In very dry, marginal habitats a population may gradually adapt and become increasingly selective towards dietary moisture and drink less fresh water.  This behaviour limits breeding and production potential.  In dry periods nyala consume both wet and dry lucerne supplements. Fallen, dry pods are an important protein source during a dry winter.

Social structure

The nyala’s social behaviour is semi-gregarious and most are found in pairs or in small groups of 3-15.  Most bull herds consist of 2-3 individuals, with a maximum of 8.  A hierarchy of dominance exists among the bulls.  Breeding groups consist of <15 individuals and include 2-3 adult ewes and 1-2 sub-adults of both genders are with or without 1-2 adult bulls. Single adult ewes that have temporarily left the group to guard their hidden lambs are often seen.  Post mature bulls tend to become solitary and often associate with other game species such as kudu, waterbuck and very small impala groups.  Male and female groups are normally separate but temporary gatherings occur at water points and at good feeding grounds.  The group structures are unstable and members constantly interchange between groups as they lack a fixed family bonding. The nyala is not territorial and the home ranges of bulls and ewes are permanent and overlap to a great extent.

Adult bulls aged >3 years frequently leave their groups and accompany a breeding group for several days for mating purposes.  More than one bull may join the same breeding group.  Young sub-adult males leave the breeding groups of their own violation at an age of 1-2 years and join bull groups.

Information table

Bibliography

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