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January 2005

Feature

 

Roan 200 years later

Rob Toms and Salomon Joubert

Roan antelope. Photo Transvaal Museum

The roan antelope, Hippotragus equinus, is one of Africa's most attractive antelopes. First described 200 years ago it is also now one Africa's most endangered antelopes despite being one of the most reproductive. 

The roan antelope was observed in 1801 by members of an expedition led by Somerville and Truter when three individuals were seen at a distance. A painting by Daniell of the roan antelope was published in 1804 the same year that it was first described by Desmarest. From a scientific point of view we have only been accumulating information about them for a relatively short time. Although the roan was only described 200 years ago, it is likely that older indigenous knowledge about these animals existed. Unfortunately little of this is readily available and is also in danger of being lost because of inadequate attention focused on the oral history of biodiversity and nature conservation.

Disappearing

In 1996 the roan antelope was classified as a low risk, conservation dependent species by the IUCN, however, the new (2004) IUCN red data book of the mammals of South Africa classifies it as vulnerable. It is a specialist grazer, rarely feeding on leaves, and this is one of the reasons it is endangered in some areas such as the Kruger Park. Without the protection of nature reserves and national parks they have little chance of survival. 

Currently, one of the best localities to see Roan in South Africa is at the Nylsvley Nature Reserve near Modimole (Nylstroom). Reference to the distribution of the roan shows that Nylsvley is on the fringe of its distribution domain where they have thrived since their introduction, the only real threat being the activities of humans.

In the Kruger National Park, there has been an alarming decline in the Roan population from 450 individuals in 1986 to about 25 in 2003, but the numbers may have increased slightly. The population is however in great danger of extinction. This was one of the most secure populations in South Africa, but now it is one of the most threatened. 

In 2003, McLoughlin and Owen-Smith investigated this problem using computer simulations and concluded that predation is the main threat. Although there are now more roan at Nylsvley than in Kruger, they only exist at small reserves because of the policy of the conservation authorities. A change in policy or a sudden outbreak of a serious disease could destroy the entire population. According to the IUCN red data book of the mammals of South Africa, the Nylsvley population fluctuates between 50 and 42 individuals. Several individuals were recently removed and sold at prices sometimes exceeding R200000. The low numbers are one of the reasons for the high prices.

Genetic diversity lost?

In another recent study, Andrew Barrie has drawn attention to the genetic diversity of roan in his MA mini-thesis. He concluded that historical translocations may have had a serious effect on their biodiversity and genetic distribution and that there may now be no genetically pure endemic populations of roan left in South Africa. Attempts at reintroductions to the Kruger National Park from Zimbabwe (Tjolotjo) and Percy Fyfe were unsuccessful.

Roan antelope Fact File

(Hippotragus equinus Desmarest 1804)

Taxonomic status

No recent in-depth study of the taxonomic status of the roan has been
undertaken though the position regarding the southernmost two subspecies, i.e. H e equinus and H e cottoni have come under some scrutiny due to imports of roan from Malawi. From available records it would appear that there is a large degree of overlap between the two.

The five generally acknowledged subspecies are:
H e equinus - mainly confined to South Africa, Zimbabwe, Mocambique and Namibia;
H e cottoni - extends from east to west across the continent through northern southern Africa (Angola, Botswana, Zambia, Malawi);
H e langheldi - to the north of cottoni, i.e. East Africa;
H e bakeri - Sudan, Ethiopia;
H e sharicus - Nigeria, Niger, Chad, and
H e koba - West Africa (Gabon, Senegal, Mali, Upper Volta, etc)

Distribution

Roan have a particularly large distribution range and occupy all savanna areas and peripheral semi-arid areas south of the Sahara. They avoid forests and deserts.

Habitat selection

Optimal habitat consists of open medium to tall grasslands fringed with an ecotone of woody vegetation. These habitats are particularly well represented by the shallow, grass-covered drainage systems associated with miombo (Brachystegia) woodlands, and are generally referred to as "dambos" (English speaking countries) or "mulolas" (Portugese speaking countries).

They are also partial to open savanna woodlands, the major features being medium to tall grasslands and fairly open woodland.

Roan are grazers and by preference do not feed lower than approximately 15 cm from the ground. They consequently avoid areas with high concentrations of short grass grazers, e.g. impala, wildebeest and zebra.

Population structures and characteristics

Roan characteristically associate in breeding herds ranging from about six to 15 individuals. In optimal situations the herds may number up to 20, 25 but seldom larger. The home ranges of the breeding herds fall within the territory of the herd bull. The home ranges and territories include winter and summer areas of activity and may be as large as 100 sq km. Adjoining herds are excluded from these territories and result in the dispersion of the herds. Roan are, consequently, never present in large numbers and may be referred to as 'low density' species.

Amongst the cows there is a dominance hierarchy and the dominant cow takes the lead in determining movement and activity patterns. Within the herd there are also subgroups of similar aged cows (calves that 'grew up' with one another). However. All cows are subordinate to the alpha (dominant) cow.

The role of the herd bull is to establish and maintain a territory, or a series of territories, within the home range of the cows. In the process he also maintains an "intolerance zone" around the herd and defends it against intrusion by other bulls of the same species.

Young bulls are tolerated in the breeding herds up to the age of two years, after which they are forcibly evicted by the herd bull and form groups of lone (or bachelor) bulls. There is a definite dominance hierarchy within the bachelor groups which enables the dominant one to take over a breeding herd if an existing herd bull is successfully challenged.

Roan cows reach sexual maturity at the age of two years and drop their first calf at the end of their third or early in their fourth year. There is no well-defined calving season and calves may be born at any time of the year. Cows come into cycle after roughly three weeks after giving birth and if they do not conceive they again come into cycle three weeks later.

The gestation period is nine months and the inter-calving period about 320 days. This implies that cows are capable of giving birth to six calves in every five year cycle. No other large antelope in Africa is known to have such a high reproductive rate.

The calves are concealed for the first six weeks after birth. During this period they are known to be visited and nursed by their dams only once during the day, i.e. early morning. During their time of concealment the calves are not known to have any functional external glands and the mother stimulates the calf to urinate and defecate and will ingest the excretions. This is believed to be a survival strategy as the elimination of any source of smell would make it difficult to detect by predators - during the period of concealment the calf relies on cover, remaining motionless for its survival.

Keystone species

Because roan have such strictly defined habitat requirements and grazing preferences, and because the survival strategies of their calves is so intimately dependent on optimal habitat conditions, roan antelope are particularly susceptible to habitat degradations. This makes the species a very sensitive indicator of the health of the ecosystems of which they form an integral part. The loss of roan from such large areas of their erstwhile distribution range serves as a tragic reminder of the loss of ecological qualities in those areas.


More information:

Rob Toms toms@nfi.co.za and Salomon Joubert sjoubert@esnet.co.za 

The authors acknowledge the following: 
- Francis Thackeray of the Transvaal Museum recorded the information about Somerville and Truter in his PhD thesis.
- Teresa Kearney of the Transvaal Museum is thanked for references and
comments. 
-Marion Dunkeld-Mengell of Friends of Nylsvley is thanked for her assistance.

 

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