Blesbok

D. d. phillipsi (Harper, 1939)

Colloquial Name

Bles is the Afrikaans for a blaze and refers to the white face marking which extends from the horns to the nose and is broken by the brown band just above the eyes.

Taxonomic Notes

See notes under bontebok. D. d. dorcas.

Description

The blesbok is very similar to the bontebok (for differences see notes on bontebok). The outline of the front hooves is slightly larger than the hind hooves in the spoor (Plate II). The horns are illustrated in Fig. 309.1. The world’s record pair originated from Molteno, Cape Province. and measured 0.508 m (Best & Best. 1977).

Distribution

Southern African Subregion
Blesbok are endemic to the Subregion. Their present distribution is to a large extent artificial as there have been wide introductions and reintroductions and they now occur in protected herds on fenced farms and reserves. Because of these wide translocations they have a wider distribution today than they had in the past. The limits shown on the map represent the area within the Subregion where naturally occurring populations were found in the past and where they still may be seen today albeit under enclosed conditions. The Magaliesberg probably represented their northern limits in this sector, yet through introduction, they may be seen today in many areas right through to the northern parts of the province on scattered farms and reserves (Kettlitz; 1962a).

From the time of the first settlers in the Cape and the commencement of exploration of the hinterland there was a gap of some 300 km between the limits of distribution of the bontebok and the blesbok. Blesbok were hunted relentlessly for their meat and hides and, as far back as 1893, Bryden (1893) noted that although they formerly occurred in countless thousands, they seldom were seen even then. They were first seen in the treks northeast from the Cape on the open grassland of the Middelberg/Richmond areas. They were common in parts of the eastern Cape Province, in the Orange Free State and northwestwards to near the Molopo River, the present boundary with Botswana. They occurred on the grasslands of the southern parts of the TransvaaI and marginally into Natal, where Anderson (1888) recorded hunting them along the upper reaches of the Tugela River. In Lesotho, Arbousset & Daumas (1846) stated that they occurred to the west of the Maluti Mountains.

Habitat

When first encountered by Europeans at the end of the 17^th century all reports indicated that they were restricted to grasslands and were not seen until the karroid areas of the central parts of the Cape Province had been traversed. Their former distribution indicates that they were confined to the Highveld plateau grasslands where water was available.

Habits

Blesbok are gregarious, diurnal grazers. Their habits are very similar to those of bontebok. They are active in the early morning and late evening and lie up during the hotter hours of the day in the shade of bushes or trees. They appear to be susceptible to heat for, during the summer months, they will seek the shade of thickets, moving deep into them. At this time the territorial males become soporific and can be approached very closely. Like bontebok; they tend to rest together in small groups.

When moving to their feeding or drinking places, or retiring to their night resting sites, blesbok string out in long single files. This continuing activity forms distinct paths. They are much more active during cool, overcast weather; but during heavy rainstorms they take shelter under trees or bushes or stand with their backs to the direction of the rain, with their heads held low.

The characteristic habit of standing in orientated groups with their heads towards the sun and their faces close to the ground is common to both bontebok and blesbok. Authorities differ as to whether they are indeed sleeping in this posture or not. They occasionally indulge in violent head shaking, snorting or stamping their feet and then running in a small circle to resume their places in the group.

As in bontebok, bachelor groups are the largest and reach peak numbers during the rut. They consist predominantly of young males and occupy home ranges in areas not occupied by territorial males (Novellie, 1975). During the autumn rut in March/April, the harem herds consist of from two to 25 females, usually about 10, attended by a territorial male which will actively drive other males away from his females. While much of this antagonism is of a ritual nature, du Plessis (1968) recorded serious fighting, the males dropping on to their knees and attempting to thrust their opponents in the flanks. These fights do not last long but are indulged in at speed and with vigour, and males have been found which apparently had been killed in these encounters. The territorial male of the harem herd courts females in oestrus, with his head held forward and his tail curled over his back in the same way as in the bontebok.

Males occupy a network of territories at least during the rut between March and May, which Novellie (1979) found in the Transvaal to have an average area of 0,023 km2 (range 0,009-0,041 km2).

After the rut territorial activities such as herding of the females and boundary encounters drop in intensity and during winter and spring territories were virtually undefended (Novellie, 1975). In November there was a rise in intensity of territorial behaviour and territorial males tended to remain in their areas for longer periods, but herding of females and aggression towards intruders were erratic. During the rut territorial males are strongly attached to their territories and will return to them if driven off. They maintain their territories by means of complicated challenge displays and actions. These include lateral presentation, head to shoulder sweeps with the head, mutual anus-smelling, horn-angling towards the opponent, digging into the ground with the horns, and in intense excitement, leaping high in the air; horn-clashing and fighting. They mark their territories by inserting grass stems in their preorbital glands so as to smear them with secretion or by wiping the glands across vegetation. They perform a process unique to the species of transferring the glandular secretion from the grass stems to the base of the horns by stroking their horns across the grass with a sideways movement of the head. Lynch (1971) found that some territorial males had a deposit of this black waxy substance up to 3 mm thick between the horn annuli. Females, bachelor males and calves also perform this process. The territorial males create dung patches in their territories and tend to lie up on them during resting periods. These middens are a focal point in the life of the territorial male, especially during the rut. It is a rendevous for social contact and a point at which many of the challenge displays are carried out in warning off other blesbok males (Lynch, 1971). Blesbok dung middens were associated often with the remains of termite mounds and provide a focus of mammal activity by virtue of their association with peripheral vegetation of high quality and the visibility afforded by patches of bare ground for behavioural and anti-predator purposes (Coe & Carr, 1978).

Snorting, with feet-stamping in the alert position, head held high, hind legs apart, and front legs straight, is also used as a ritual challenge. All these displays, which usually are sufficient to cause withdrawal of the trespasser, serve to minimise actual fighting. Aggression between adult females in harem herds has been recorded by Lynch (1971). However, this is confined to threatening with never reaches the extent of horn-clashing.

Blesbok have interdigital glands and pawing, especially of the dung heaps, by territorial males may be an additional factor in marking. It also occurs in conjunction with other challenge displays such as face-wiping, horning or defecating. Challenge rituals are terminated usually by mock grazing, the individuals then moving apart. Should one, however, raise its head at this juncture, it may be taken as a threat and horn-clashing follows.

During the cold, dry season from about June to August very large aggregations, consisting of all sexes and age groups, are found. Lynch (1971) recorded up to 650 individuals in one such aggregation. Female herds, however still maintain their identity, tending to frequent particular areas. Both the female herds and aggregations have well defined home ranges at this time. By September these large aggregations begin to split up into female and bachelor herds and territoriality among adult males becomes noticeable from November, reaching its highest intensity about April. Veld burning can cause disruption of the social organisation, for fresh sprouting grass is much sought after by blesbok and the entire population may move to an area after a burn.

Unlike the bontebok, where the general herd structure remains unchanged throughout the year, the social organisation of the blesbok undergoes marked structural changes during the months of the year. Blesbok females are not associated intimately with the territorial males throughout, only during the rut, and do not occupy the same home ranges on a year round basis (Lynch, 1971).

Food

Blesbok are predominantly grazers, although van Zyl (1965) recorded that they will browse occasionally. They are partial to sprouting grasses which appear after a burn, and will move on to burnt areas even before the green flush is apparent. Where these areas are some distance from a water supply, they will move off it only for the purposes of drinking in the early morning and late afternoon, then return to it. During winter du Plessis (1968) recorded that blesbok enter a period of minimal activity which lasts until the grass sprouts with the onset of the rains. During this time they graze lightly and selectively in small groups. Du Plessis (1968) stated that blesbok avoid grasses with more than one season's growth and showed that there is a marked difference in the species of grasses utilised on burned as opposed to unburned areas. Among the species of grasses eaten some, such as Setaria flabellata, are important in winter but remain untouched in summer, indicating a seasonal change in the species utilised. Some species such as Ctenium concinnum; bristle grass, Aristida junciformis; and sour grass, Elyonurus argenteus, are consistently avoided. Du Plessis (1968) gave a list showing the relative importance in the diet of six species of grasses from a burned and seven from unburned areas at Rietvlei, Transvaal. The four principal species from the former are red grass, Themeda triandra; weeping lovegrass, Eragrostis curvula; Chloromelas sp and Setaria nigrirostris, and from the latter Eragrostis pseudosclerantha; T. triandra; E. curvula and Chloromelas sp.

Reproduction

Blesbok are short-day seasonal breeders, mating in autumn, and further oestrous synchronisation is induced by the presence of the male (Marais, 1988). The oestrous cycle was determined by measuring plasma progesterone peaks and is about 30 days (Marais, 1988). The bulk of the lamb crop is born between November and January, with a peak in December (Skinner et al., 1974). Where parturition occurred as late as February/March this was confounded by dystocia, females dying while giving birth, so that although breeding is theoretically possible outside autumn, other factors limit this occurrence (Marais, 1988). Prior to the rut, which occurs from March to May, territorial males start to herd females in an endeavour to retain them within their territories. Exhibiting the courting display with their heads held forward, the horns lying back and their tails curved over their backs, they advance on the females with stiff legs and, moving in a semi-circle in front of them, cause the females to cluster. Once they have grouped the females in their territory they will keep them there by circling them from time to time. Lynch (1971) recorded a territorial male that successfully herded 34 females. In spite of this, females do slip away from harem herds to join others and whole harem herds may move from territory to territory. Well-fed blesbok ewes kept in proximity with the ram cycled throughout the year. The length of the cycle, as indicated by cyclic production of progesterone, was 28-32 days. During the breeding season

when a ram was introduced to ewes which previously had been isolated from the ram, this caused the previous non-cyclic ewes to cycle in synchrony. This synchronisation caused the bulk of the lamb crop to arrive within a short period. The short autumn mating season is timed when nutrition has been adequate for several months, improving body condition and the chances of ovulation and conception. Following gestation, lambing occurs after the first summer rains when nutrition is again adequate for lactation and growth (Marais, 1988).

Female blesbok become sexually mature at about two and a half years old, in some cases possibly earlier (du Plessis, 1968). Skinner et al. (1974) gave the gestation period as about 240 days and a single young is born at a birth weighing six to seven kg. Females remain with the herd to give birth, which usually takes place in the forenoon. Females do not eat the afterbirth as do some hartebeest. The cream-coloured calves can stand up a few minutes after being born, but are unsteady. Some 20 minutes later, however, they can run with their mothers. They start suckling when about an hour old.

Yearlings are very interested in new-born calves and have to be chased off by the female. Females will suckle their own calves only, driving others away, and when calves get separated from their mothers they bleat loudly, the mothers responding with deep grunts, until contact is re-established.

Calves are weaned at about four months old but remain attached to their mothers for another six months, then tend to leave them, and will form calf groups either within the female herds or join mixed aggregations or bachelor herds. Male calves may remain in the same herd as their mothers until calving time, but females sometimes remain with their mothers for up to two years.

Females have a 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.