Oribi

Appearance

The oribi is a small, slender antelope; it reaches nearly 50–67 centimetres at the shoulder and weighs 12–22 kilograms. The head-and-body length is typically between 92 and 110 centimetres. Sexually dimorphic, males are slightly smaller than females. This antelope features a slightly raised back, and long neck and limbs. The glossy, yellowish to rufous brown coat contrasts with the white chin, throat, underparts and rump. The bushy tail, brown to black on the outside, has white insides. The subspecies show some variation in colouration; "O. o. ourebi" is a rich rufous, while "O. o. hastata" is yellower.

Only males possess horns; the thin, straight horns, 8–18 centimetres long, are smooth at the tips and ringed at the base. The maximum horn length, 19.1 centimetres, was recorded in 1998 from Malawi. The oribi has at least six different, well-developed scent glands. The body has several modifications, such as the large fossae below the eyes, to accommodate such a large number of glands. Females have four teats.

Distribution

This antelope is highly sporadic in distribution; it occurs mainly in eastern, southern and western Africa, ranging from Nigeria and Senegal in the west to Ethiopia and Eritrea in the east and southward to Angola and the Eastern Cape. It is feared to be extinct in Burundi.

Behavior

The oribi is diurnal, though some activity may also be observed at night. It rests in cover during rain events. Unlike all other small antelopes, oribi can exhibit three types of mating systems, depending on the habitat – polyandry, polygyny and polygynandry; polygyny tends to prevail as the female-to-male ratio increases. A study suggested that polygyny is preferred in areas of high predator risk, as it leads to formation of groups as an anti-predator measure. Small herds of up to four members are also common.

Males defend their group's territory, 25–100 hectares large; female members may also show some aggression and drive away intruders. A study showed that the number of females that visit the male's territory depends on the appearance of the male's horns. Males mark vegetation and soil in their territories by preorbital gland secretions and excrement; the intensity of marking increases with the number of male neighbours. Dominant males tend to have greater access to females in and around the territory than other males. An important feature of the social behaviour of oribi is the "dung ceremony", in which all animals form temporary dung middens. Oribi at least three months old have been observed giving out one to three alarm whistles on sensing danger. These whistles are more common in adults than in juveniles, and males appear to whistle more. Common predators include carnivorans such as jackals.

Habitat

The oribi occurs in a variety of habitats – from savannahs, floodplains and tropical grasslands with 10–100 centimetres tall grasses to montane grasslands at low altitudes, up to 2,000 metres above the sea level. Recently burnt areas often attract groups of oribi. The choice of habitat depends on the availability of cover needed to escape the eyes of predators. Population densities typically vary between 2 and 10 individuals per km2; however, densities as high as 45 individuals per km2 have been recorded in tropical grasslands that receive over 110 centimetres of annual rainfall and open floodplains. The oribi's range overlaps with those of larger grazers such as the African buffalo, hippopotamus, hartebeest, Thomson's gazelle and topi. These separate species often occur in close proximity to each other, increasing predator vigilance.

Reproduction

Both sexes become sexually mature at 10 to 14 months. A seasonal breeder, the time when mating occurs varies geographically. Mating may peak in the rainy season. When a female enters oestrus, she seeks the company of males. During courtship, the male will pursue the female, test her urine to check if she is in oestrus and lick her rump and flanks. Gestation lasts for six to seven months, following which a single calf is born; births peak from November to December in southern Africa. The newborn is kept in concealment for nearly a month; the mother pays regular visits to her calf to suckle it for nearly half an hour. Males may guard their offspring from predators and keep away other males. Weaning takes place at four to five months. The oribi lives for 8 to 12 years in the wild, and for 12 to 14 years in captivity.

Food

Primarily a grazer, the oribi prefers fresh grasses and browses occasionally. Grasses can constitute up to 90% of the diet; preferred varieties include "Andropogon", "Eulalia", "Hyparrhenia", "Loudetia", "Pennisetum" and "Themeda" species. Mineral licks are also visited regularly. Oribi have been observed feeding on flowers and "Boletus" mushrooms. Groups of oribi congregate in the rainy season, when grasses are abundant.