By Amy Schoeman
Imagine a larger and darker version of the graceful impala with its shiny reddish coat and long slender legs, add a distinctive dark blaze to its muzzle, and you have the black-faced impala, Aepyceros melampus petersi, a subspecies found in the wild only in south-western Angola and north-western Namibia.
The evolution of this interesting subspecies is the result of its isolated occurrence, the ordinary impala having a wide distribution in the eastern woodlands of Africa, from northern Kenya southwards to northern KwaZulu Natal in South Africa.
The black-faced impala’s definitive dark blaze extends from its nostrils to the top of its head, and its tail is long and very bushy. An adult male has a mean mass of 63 kg, the female about 50 kg, considerably larger when compared to an ordinary impala male with its mean mass of 50 kg and female which weighs approximately 40 kg. The upper parts of the black-faced impala’s body lack the rich reddish-brown colour of the ordinary impala, being duller brown with a rich purplish black sheen.
According to Shortridge, black-faced impala used to occur as far south as Kaoko-Otavi. Today this interesting animal’s natural distribution is limited to the northern and southern banks of the Kunene River, in Namibia in northern Kaokoland, where they are seldom encountered further south than 30 km from the river.
Following a timous relocation programme by the Namibian Department of Nature Conservation in the sixties, about 1 500 black-faced impala currently inhabit the Etosha National Park, with small numbers occurring on private game reserves and farmlands. Ordinary impala occur naturally in western and eastern Caprivi, while small numbers were translocated from South Africa’s then Transvaal and Natal provinces to the Daan Viljoen Game Reserve, the Waterberg Plateau Park, private game reserves and several farms.
On account of recurrent droughts, hunting pressure and competition from livestock, conservationists in the former Department of Nature Conservation expressed concern about the continued survival of this rare and endangered species in Namibia. There was also the question of whether this impala was merely a variation of the ordinary impala, or whether it was a distinct subspecies.
Polla Swart, who subsequently became the Director of Nature Conservation in the Ministry of Environment and Tourism, had then shortly joined the Department. His first research project was to establish exactly this. The results of his study established beyond a doubt that the black-faced impala was a subspecies in its own right. After further research, moreover, the conclusion was reached that it should be classified as a separate species altogether. It made sense, therefore, to capture black-faced impala in northern Kaokoland for relocation in Etosha, rather than bring ordinary impala all the way from the Transvaal and Natal in South Africa, thereby ensuring the continued survival of the local species’.
This prompted an extensive capture and relocation programme. A total of 266 animals were caught, mostly in the environs of the Kunene River, and transported to the Kaross Khoabendes area in the western sections of Etosha. After a period of quarantine they were moved to other parts of the park such as Ombika, Olifantsbad and Namutoni in the east. They adapted extremely well and by the eighties their numbers had increased to over 1 000. As the tendency to reintroduce game onto commercial farmlands gained momentum, small numbers were sold or auctioned to farmers with suitable habitats, further ensuring the survival of the black-faced impala in Namibia.
Are they a separate species?
The evolvement into a separate species normally occurs when for geographic reasons an animal has an isolated distribution. The black-faced impala of the Kunene are separated from the ordinary impala of Kavango and Caprivi by the North Central Region (the former Owamboland), a barrier of approximately 800 km in which they cannot survive, as they need to be near a permanent water source. The impala of the north-east could migrate to other areas such as Zimbabwe, Zambia and South Africa, but because of the absence of perennial rivers other than the Kunene, the impala of the north-west had nowhere to go.
For a subspecies to be reclassified as a separate species the difference needs to be structural. In the black-faced impala’s skull the ends of the premaxillaries are about 15 mm away from the lachrymals, whereas in the ordinary impala they are less than 11 mm away. While local researchers are of the opinion that this should be sufficient to have the animal reclassified as a separate species, it is currently still regarded as a subspecies of the ordinary impala.
This article appeared in the 2001 edition of Conservation and the Environment in Namibia.