Roan

Roan are a large antelope, second only in size to eland. Adult males have a shoulder height of about 1.4 metres and weigh slightly under 300kg. Females are slightly smaller and lighter. Both sexes carry horns which rise from the head in a uniform backward curve and are ridged. The longest pair of horns on record (99 cm) are from a trophy taken in the Tokwe Valley, Zimbabwe (Best and Best, 1977). The females' horns are smaller than the males. The body coat is greyish brown with touches of rufous colouring which varies amongst individuals. The legs are darker brown than the remainder of the body and the animal possesses a noticeable mane. The most distinctive features are the facial markings which resemble a black balaclava mask with elongated white 'cut-outs' around the eyes. The ears are unusually long with dark brown tufts on the tips.

Social Structure

The social structure of a roan population consists of nursery herds, bachelor groups and dominant bulls (Smithers 1983). They are gregarious animals with breeding herds usually numbering 10-20 individuals - although as many 80 have been recorded in a single group. Breeding herd home ranges vary from 60 - 100 km2 (Erb 1993). Social hierarchies are well developed in both sexes. Males are forced out of the herd at 2-3 years of age and either become solitary or form bachelor groups. Breeding groups are usually led by the dominant female.

Territoriality

Depending on the situation, roan may or may not exhibit territorial behaviour. In some areas dominant bulls have an 'activity zone' rather than a territory and defend a harem of females, e.g. in Kruger National Park a specific male is usually associated with a particular female group throughout the year (Joubert 1976). On the other hand, there are instances of males establishing territories through which a group of females with their offspring may move, e.g. in the Waterberg (Erb 1993). The determining factor for which of these two modes of behaviour is adopted may be the degree of aridity. Roan may be forced to move over a large range in low rainfall areas prone to sporadic droughts - in which case it would seem pointless to defend a territory. Where the rainfall is higher and less erratic or in areas which are relatively small and constrained (e.g. in the Waterberg) the situation may be more favourable for the males to invest in territory.

This ability to alter their system of range use according to circumstances ought to enhance their survival.

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Sable

Sable are slightly smaller than roan, with adult males standing under 1.4 metres at the shoulder and weighing about 230kg. There is a distinct dimorphism: older males have shiny black coats whilst females are dark brown. Subadults and juveniles of both sexes tend to be a lighter shade of brown. All have white bellies with the colour extending inside the rear legs and up to the base of the tail. The face is marked longitudinally with white stripes extending from each eye towards the muzzle. Both sexes carry horns but the fully developed male horns are far larger than those of the females. The horns sweep back from the head in a characteristic curve, with the largest trophies from the southern African region being just over 50 inches.

Social Structure

As with roan, sable are gregarious, form similar-sized herds and their social structure consists of nursery herds, bachelor groups and dominant bulls (Grobler 1978).

Territoriality

Unlike roan and tsessebe, sable bulls appear to be strictly territorial and are never attached to a mobile group of females. The home ranges of territorial males lie between 25-40ha whereas breeding herds use ranges of 2-5 km2. Juvenile males are evicted from herds at about 3 years old by dominant males and, at 5-6 years of age, they are ready to establish their own territories, either by challenging dominant males or by dispersing to set up a new territories.

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Tsessebe

Tsessebe adult males stand about 1.2 metres at the shoulder and weigh about 140kg. The average female body weight is slightly less than 130kg. The general colour of the body is dark reddish-brown with a purplish sheen. The upper part of the head and muzzle is almost black. The colouration of the flanks and withers are darker than the remainder of the body giving the appearance of a 'watermark' from mid-body downwards. There is some yellowish colouring on the base of the tail, the back of the ears, the insides of the hind legs and on the abdomen. Tsessebe have a characteristic body shape which slopes downwards towards to the rump. Both sexes possess horns which rise close together in the centre of the head and bend outwards and upwards in a uniform curve. A record trophy of 47cm (Best and Best, 1977) was taken in northern Botswana.

Only behavioural attributes which have implications for management are considered here. Species which are strongly tied to territories are likely to be vulnerable in semi-arid environments when drought or habitat changes alter their situations. Species which have the flexibility to be able to undertake local migrations when water or food is limiting may have a survival advantage. It may only be necessary for the females of the species to possess this attribute to ensure the persistence of populations.

Social Structure

Although tsessebe share similar social structures with both roan and sable, subtle differences also exist. Average herd sizes are generally smaller, e.g. (excluding juveniles) less than 4 in northern Botswana (Child et al 1972); less than 6 in Zimbabwe and Kruger National Park (Grobler 1973, Joubert and Bronkhorst 1977) and about 8 animals in the P.W.Willis Nature Reserve, South Africa (Garstang 1982).

Territoriality

Dominant tsessebe males establish fixed territories but, unlike sable, a specific harem herd is usually associated with each bull. This harem herd also has a fixed home range but it may not necessarily coincide exactly with that of the bull because of the partiality of females for particular habitat types. Garstang (1982) found that these harem home ranges overlapped in the hot/wet season but not in the cool/dry season. There is a high degree of fidelity to breeding herds (i.e. no new animals from other groups are permitted to join the herds). Tsessebe in Kruger National Park are fairly sedentary under such a system (Joubert and Bronkhorst 1977). However, other social structures have been observed where harem herds move between male territories at will - as in the case of sable. Child et al (1972) observed seasonal changes in home ranges at Kwhai in Botswana.

This ability to alter their system of range use according to circumstances ought to enhance their survival.

Intra-specific aggression and competition

Intra-specific aggression and competition are established behavioural characteristics of all three species and are an adaptation to ensure sufficient good quality nutrition. However, they are unlikely to play a significant rôle at the low densities at which most of the populations in Namibia occur. They may be factors to be taken into account in managing enclosed populations on commercial farms or in small protected areas such as the Waterberg Plateau Park. Wilson and Hirst (1977) note that when roan and sable are constrained on small properties or areas of low quality habitat, intra-specific aggression and competition with other species intensifies.