Bontebok

Damaliscus dorcas (Pallas, 1766)
D. d. dorcas (Pallas,1766)

Colloquial Name

The name applies to their "many coloured " coats which include white and several shades of brown, in parts glossed purple. While it is not normal practice to apply colloquial names to subspecies, the colloquial names bontebok, D. d.dorcas, and blesbok, D. d. phillipsi, are both well entrenched and warrant retention.

Taxonomic notes

Previously the bontebok and blesbok were considered to be separate species, but the consensus of opinion today is that this cannot be upheld and they are both considered as subspecies of  D. dorcas.

Chromosome number is 2n=38 (Wurster & Benirschke, 1989) Recently (Fabricius, van Hensbergen & Zucchini, 1989) it has been shown using a discriminant function analysis that the two subspecies and their hybrids can be separated on the basis of colour pattern.

Description

Bontebok are medium-sized antelope standing about 0,9 m at the shoulders. Adult males have a mean mass of 61,0 kg (Table 309.1), females are lighter and slightly smaller. It is difficult to recognise the sexes in the field, except that the horns of the females are more slender than those of the males and hardly thicken up at the base. The adult males are generally darker in colour and their white scrotums are conspicuous.

Table 309.1

Mass (kg) of adult bachelor bontebok rams, D. d. dorcas, from the Bontebok National Park, Swellendam (Skinner, Dott, de Vos & Millar, 1980).

                        Males
               x                 n               Range
Mass    61,0             24             59,6-63.6

At close quarters the back is seen to be rust-brown in colour. The crown of the head, the sides of the~ face and neck, the flanks, thighs and front portion of the rump and upper parts of the limbs are dark brown to nearly black. The sides of the face and neck, the flanks and the upper parts of the limbs are glossed with a purple sheen. The front of the face is white from the base of the horns to the nose, this blaze narrowing just above the eyes. However, there is considerable variation in this character; David (1970) showed that in 19% of bontebok the face blaze is divided by a brown band as it is in the blesbok.

The under parts, the lower parts of the limbs and the rump patch are white, with a dark brown suffusion just below the knees, on the front surface of the forelegs. The ears are brown, slightly lighter in colour than the body. The tail is white for about half its basal length and the remainder is dark brown or black with long black hair towards the tip.

Spoor-Plate II.

Detailed examination of the micro structure of bontebok and blesbok hair shows no specific variation apart from colour (Fig. XLII.1) (Keogh, 1983). The principal differences between the bontebok and the blesbok are summed up by Bigalke (1955) as follows:

The pure white patch on the rump of the bontebok is probably the best character in the wild in distinguishing them from blesbok,

Both the bontebok and blesbok have preorbital glands (see Habits). They have pedal glands on the forefeet only and no inguinal glands. The preorbital glands are larger in the male than in the female and exude a yellowish-black sticky secretion, which mats the hair and forms tear marks on either side of the face. Territorial males after applying this secretion to grass stems transfer it from them to their horns, a procedure which appears to be unique to the bontebok (Lynch, 1974).

Their long face, high withers and sloping hindquarters give them a characteristic outline compared with other medium-sized southern African antelope, which is reminiscent of that of their close relatives, the wildebeest and hartebeest.

Both sexes carry the ridged horns which, rising from the top of the head, curve backwards and outwards and then slightly forwards towards the un-ridged tips.

Distribution

Southern African Subregion
Bontebok are confined in their distribution to a restricted area in the southwestern Cape Province, lying between Bredasdorp and Cape Agulhas. Historically their area of occurrence was somewhat larger, extending from Bot River to Mossel Bay and inland to the Sondereind and Langeberg mountains (Bigalke, 1955). Many of the early travellers first saw them near Caledon, where Isaac Schrijerer's Journal of 1689 recorded that more than 1 000 were seen. Sparrman (1786) also recorded their presence in this area. In these early times there was a measure of confusion in identification between the bontebok and the blesbok. Cornwallis Harris (1840) wrote of "bontebok" as far north as the Magaliesberg in the Transvaal, which were certainly blesbok. Since the time of the early settlement in the Cape there was a distance of some 320 km between the limits of distribution of the two. Bryden (1936) noted that blesbok were never found in the Cape Province, west of Colesberg, and did not occur in the Great Karoo. At one time the species D. dorcas must have had a wide and continuous distribution in southern Africa. Through climatic changes at some geological period of time it became split into two populations which, over the intervening ages, have diverged in characters, leading to the recognition of the two subspecies we see today, the bontebok, D. d. dorcas, and the blesbok, D. d.phillipsi.

It is appropriate that tribute be paid to Mr. P . V. van der Byl, his son, Mr. A. van der Byl, and the van Breda and Albertyn families, for without their recognition of the perilous situation of the species they might well have become extinct. The van der Byls took steps in 1837 to set aside a portion of their farm "Nacht Wacht" near Bredasdorp as a reserve for a nucleus of some 27 individuals. This example was followed by adjoining landowners on the farms De Groote Eiland, Bushy Park and Zoetendals Vallei (Bigalke, 1955). In 1931 the first Bontebok National Park was proclaimed on an area near Swellendam and 84 bontebok were moved to it by truck. By 1969 it was estimated that the numbers had grown to around 800. Since then the National Parks Board of Trustees have made available their surplus stock to farmers and reserves in the Cape Province and by these measures have ensured the survival of the species for the future. Bontebok, nevertheless, remain the least common antelope in the Southern African Subregion.

Habitat

Bontebok live in a narrow sector of coastal plains at an altitude of from 60 to 200 m above sea level within the Cape fynbos zone, a sandy, alluvial plain with stony ridges and gravel terraces. The plain provides the grasses (see Food) on which they feed, and an association of shrubs 300 to 700 mm high, including renosterbos, Elytropappus rhinocerotis; Aspalathus spinosa; Montinia caryophyllacea; Oedera imbricata; Berkheya armata; and Corymbium scabrum, which provide shelter (David, 1973). Water is an essential habitat requirement and is found in the many small streams and rivers which occur and whose banks provide, in their riparian Acacia associations, more substantial cover in the form of small trees. The habitat lies in a winter rainfall area, rain falling in all months of the year, with a peak during spring from September to November, which is the lambing season. The average mean annual rainfall is about 550 mm. Areas of short grass, cover and drinking water are among their essential habitat requirements.

Habits

Bontebok are a diurnal, gregarious, grazing species. Their social organisation consists of territorial males, females herds and bachelor groups. The territorial males establish and maintain a mozaic of territories varying in size from four to 28 ha on an all year round basis. Some males may hold their territories for much longer periods, even for the duration of their adult lives. They rarely manage to establish a territory before they are three years of age, generally five years (David, 1970). They acquire these by deposing a territorial male from his territory or by establishing a new one. They defend these from trespass by other males by a complicated system of ritual displays, seldom if ever resorting to fighting.

Female herds consist of a small number of adult females with their young, in total numbering up to about eight, which are non-territorial and wander at will over the home ranges of the territorial males. During the rut the territorial male courts females when they enter his territory and takes

steps, by herding and ritual displays, to entice them to remain within it (see Reproduction). There is a hierarchy among the members of the female herds, established by threat postures, horn-clashing or battling with the horns. Adult females demonstrate against strange attentive males, driving them off with a bucking bounce, kicking out with the hind legs.

Bachelor groups are much larger, consisting of males of all ages, including old decrepit males and young males. They may also include a small number of females. They are an important unit in the social structure as they provide security for young developing males, who may later become territorial males, a haven for decrepit old males, deposed territorial males, which are accepted amicably as members, and a temporary refuge for immature females. There is no hierarchy within bachelor groups and no aggression between members. Play-fighting between yearlings may occur, consisting of horn-twisting and head-pushing (David, 1970).

Young males leave their mothers at about 12 months old, when she produces her next offspring. They may remain solitary for a time but eventually join bachelor groups until sexually mature. They are not forced out of the female herds by their mothers or by the territorial males, as happens in the case of wildebeest and impala, but leave of their own accord. Bachelor groups are loose associations and when, in their wide movements, they enter the territory of a territorial

male, they may so overwhelm him by numbers that he is not able to drive them out. While he may chase individual males, he eventually gives up and confines his actions to various threat postures. Normally males in bachelor groups give way to territorial males without encounter. Yearling females which join bachelor groups remain with them until they are about two years old before joining the nursery herds.

David (1973) described in detail some 30 challenge reactions used by territorial males in driving off trespassing males which include lateral presentation of the body to intruders, head-dipping and nodding, alarm-snorting, bucking, bouncing with kicking with the hind legs, defecating and urinating postures, soil-horning and head to tail sniffing, the individuals standing side to side. All these usually end up with the trespasser moving off and actual encounters are rare.

While the many complicated challenge threats are all used by the territorial male in retaining his dominance in his territory, the most important seems to be the manner in which he advertises his possession of it. He will assume the "proud" posture with head held high, ears extended sideways, often standing on raised ground so that he is clearly visible. Marking of the territory by defecation and urination used by other species is not important to the bontebok. Their latrines are scattered about the territory and generally are disregarded by other males.

Territorial males endeavour to retain adult females if they show signs of leaving their territories. They may do this by courting them with a display consisting of an approach with the muzzle pointed forward, horns laid low along the back and tail curled upwards. They display in this way and prance up to her or run straight at her with head held high and ears forward. If the female is determined to leave, however, the male may allow her to do so. If the herd is disturbed, the territorial male takes up a defensive position in the rear, standing broadside on in a wide stance or in the urinating posture, which has been interpreted as a symbolic threat. The scent-marking which they carry out by applying the black secretion of the preorbital glands to grass stems, is not recognised by others.

Horning of bushes or of the latrine patches by territorial males, often used on trespass by bachelor intruders, was suggested by David (1973) to be a threat display. Serious fighting is rare and even when fighting occurs no injuries result. Contestants may drop on their knees with their foreheads close to the ground and feint at each other without actual contact. These encounters only last a few seconds before one gives up and retires.

While the territorial males invariably use latrines, a central one in the territory is often used to lie on during the day. The bachelor males defecate randomly, as do the females and juveniles.

The periods of greatest activity are in the early morning and late afternoon. They rest during the hotter hours of the day in thickets, where they tend to cluster together. During periods of heavy rain they seek the shelter of trees or stand facing away from the wind with their heads held low.

In common with the blesbok, bontebok have a characteristic habit on hot days of standing in orientated groups facing the sun with their heads held low. They remain alert during this time, occasionally shaking their heads and snorting or stamping their feet, then running in a circle to resume their place in the group.

Food

Bontebok are almost exclusively a grazing species, with a preference for feeding on short grass. Nolte (1973) examined the fresh rumen contents of bontebok from the De Hoop Provincial Nature Reserve, Cape Province against the epidermal characters of a series of grasses collected in the Reserve and ascertained that they contained the following percentage of various grasses:

Species                                                 Percentage

Bromus sp                                                25

Pseudopentameris rnacrantha                      22

Plagiochloa uniolae                                    16

Eragrostis capensis                                    14

Bromus diandrus                                         5

Merxrnuellera stricta                                    3

Undet                                                      15

Reproduction

Bontebok are short-day seasonal breeders, mating in early autumn in the Bontebok National Park, where the rut takes place between the months of January to mid-March, with some activity continuing until April (David, 1973). The territorial males court the females with a display involving tail over the back and holding the head low with outstretched and the tail horizontal. Flehmen does not occur in bontebok. A male may sniff the vulva of a female and if she is not receptive she will run around him closely to avoid his attentions. During this "mating circling" the female holds her head low in the submissive attitude. During the rut the frequency of the courtship display may be as high as once an hour, but is not confined to the period of the rut and may be performed in all seasons of the year. When the male performs to females about to leave a territory, it may actuate them to remain (David, 1970). The annual cycle in the male matches that in the female (Skinner et al., 1980).

Conception rate is influenced by rainfall (which in turn affects grass cover) prior to the breeding season (Novellie, 1986), as well as food availability, as influenced by competition for food by grazers. The gestation period is between 238 and 254 days. Lambs are born in the spring, between

September and November, with late arrivals up to the end of February, the peak months being September/October. Females become sexually mature at just over two years old, having their first lambs at about three years old. The young females remain with their mothers after their new lambs are born, as a member of the herd (David, 1975).

Females have one pair of inguinal mammae.

From "The Mammals of the Southern African Subregion" by permission of Professor John D. Skinner (M.Sc. Ph.D. F.I.Biol. F.Z.S. F.R.S.(SA)), Director Mammal Research Institute of the University of Pretoria.