Cross-breeding threatens the black wildebeest

Published Jan 31, 2003


By Marleen Smith

The black wildebeest, which evolved around a million years ago on the central plains of southern Africa, is now under threat due to cross-breeding with its ancestral species the blue wildebeest, scientists warn.

Palaeonthologist James Brink and terrestrial scientist Savvas Vrahimis have joined hands in an effort to save the genetic integrity of the black wildebeest, which is one of only a handful of species endemic to the central interior of South Africa.

Vrahimis, who works for the Free State department of tourism, environmental and economic affairs, says the black wildebeest is currently categorised as being at lower risk on the Red List of Threatened Animals, compiled by the International Conservation Union (IUCN). However, on the updated list to be published soon it is likely that the species may be listed as vulnerable.

Although they are still safe from extinction, black wildebeest numbers are relatively low, he says. Their largest threat is hybridisation with blue wildebeest, as the two species are often kept within the same camps on game farms.

It is estimated that there are presently more than 120 private properties in the Free State, Northern Cape and Kwazulu-Natal alone where black and blue wildebeest are housed together.

The hybrids are fertile. Although first generation hybrids are easily identifiable, hybrids interbred with pure stock black wildebeest are difficult to recognise on appearance alone. This is where the danger lies.

Already, large populations of black and blue wildebeest that were housed together had to be destroyed because of hybridisation, Vrahimis says.

Cross-breeding occurs easily because the two species have similar mating and calving periods, as well as fairly similar behaviour. As the black wildebeest bulls are far smaller than their blue counterparts, they are chased away from the mating cows and the black cows are fertilised by the blue bulls.

Although the natural habitats of black and blue wildebeest overlapped during historical times, hybridisation was apparently not a problem because they were not enclosed by fences, as is the case in modern South Africa, Vrahimis says.

The black wildebeest is not only one of a few species endemic to the central interior. It is also special because it evolved locally and did not immigrate after its evolution from elsewhere, says Brink of the National Museum in Bloemfontein.

The oldest fossil records of separation between the two species are dated to a little less than a million years ago. Over thousands of years the black wildebeest has thus developed into a separate species that is smaller with distinct adaptations that reflect specialised breeding behaviour.

The shift to its more territorial behaviour is linked to the evolution of treeless grasslands in the central interior of southern Africa over a million years ago, Brink says.

"Some of the black wildebeest's characteristic features, such as larger eye sockets, a reduced nasal area and forward pointing horns reflect its more aggressive behaviour. This is due to the need for visual patrol and defence of breeding territories in a treeless habitat without visual obstruction."

Brink says palaeonthological evidence accordingly indicates that, at the time of the split between the two species, the interior became far less bushy, with fewer trees and open, grassy plains. He thus suspects that the black wildebeest ancestors adapted accordingly, depending more on sight to patrol their territories.

Blue wildebeest, on the other hand, have a more flexible breeding behaviour, which does not necessarily include territoriality.

The black wildebeest's adaptation to an open habitat is clearly evident when the species is kept in a closed, more bushy environment. Experiments showed the dominant breeding males removing bush and tree branches with their horns and destroying tree canopies in order to have an open view to all sides.

Concerned conservationists and game farmers in the Free State have now initiated a process through which new regulations will hopefully be accepted to prevent the keeping of black and blue wildebeest within the same enclosures.

It is hoped that such regulations will eventually be in force across the country, and may be the only hope for the survival of the black wildebeest.

Without it the species will probably become another of many sacrificed in the process of human encroachment upon the natural habitats of free-roaming animals. - Sapa

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