All the World's Antelopes: Sables and Other Horse-Antelopes

Sable antelope (male)

The hippotragines are one of several small subfamilies of antelope. Small that is, in terms of number of species, because physically they are quite large. The name literally translates as "horse-goat", but that second part is often used taxonomically as a term for antelopes, so "horse-antelope" might be closer to the intent. It was coined in 1845, partly on account of the physical build of the animals, with their long legs and muscular, horse-like necks.

The subfamily includes the oryxes and gemsbok, but arguably the most horse-like members of the group are the sable antelope (Hippotragus niger) and its closest relatives. Sable antelopes stand around 140 cm (4'7") at the withers, which is almost exactly the official height that separates full-size horses from ponies. They weigh between 160 kg and 230 kg (350 and 510 lbs), which is well within the range for domesticated ponies, indicating a slighter build than animals bred, in part, to bear the weight of humans. Their shape, however, is quite horse-like, an effect accentuated by the presence of a clear mane down the back of the neck.

The name comes from the colour of the adult males, which is jet black over most of the body, with clearly offset white underparts and rump. The chin and the sides of the face are also white, with a narrow black stripe running down the middle of the cheeks. Females, and males under three years of age, are instead a dark chestnut, but maintain the same white markings. The horns are long and curved into an almost scimitar-like shape, with numerous rings along their length. They reach as much as 165 cm (65 inches) in the largest males, but are about a third shorter in the females.

Sable antelopes live in southeastern Africa, from the southern tip of Kenya to northern South Africa. Four subspecies are currently recognised, with the most northerly sometimes being considered a distinct species; they vary in details of average size, the colour shade of the females, and the exact shape of the facial markings. Among these is the "giant sable antelope" of Angola, which is slightly larger than the others, with larger horns. Genetic studies have revealed that this diverged from the other subspecies around 170,000 years ago, during the second-to-last Ice Age. While sable antelopes as a whole are reasonably common, partly due to about 25% of them being kept on private land, the giant species is almost extinct, with fewer than a hundred adults thought to be alive and subject to near-constant poaching.

They inhabit open savannah woodlands dominated by miombo (a leguminous tree common across much of southern Africa). Highly dependent on open water, they stick to river valleys and lusher grasslands during the dry season, but they move onto higher slopes during the wet season, where greater tree cover can afford them better protection. They tend to avoid the most open of plains, but anywhere with good grass growth will do in a pinch. 

Studies of their diet indicate that they eat almost nothing but grass, although they are surprisingly picky about the grasses they prefer, with one study showing that 90% of their diet consists of just four species. In addition to panicgrass, red grass, and speargrass, this included a species of Chrysopogon that, while relatively common, is avoided by zebras and other local antelopes, allowing them to live alongside one another without competition. They also frequent salt licks, and have been known to chew on dry bones for their mineral content.

Sable antelope are most active in the morning and early afternoon, resting during the hottest parts of the day. Females live in herds of between 15 and 25 individuals, led by the oldest member, at least until she becomes physically unfit. The dominance hierarchy within the herd is unusually strict and long-lasting, with females often fighting with one another, especially when they are ready to mate, and being highly aggressive towards any other female they consider an intruder. The herds themselves are also mutually hostile, although they will gather together in larger groups in places where the grass is especially lush and they can feed without having to battle for resources.

Adult males, in contrast, mostly travel alone, each maintaining a territory of 25 to 40 hectares (65 to 100 acres), far smaller than the wide ranges over which the females travel of 25 km² (10 square miles) or more. Nonetheless, males will attempt to keep passing females within their territory for as long as they can manage; their success rate at this is apparently widely variable, with some keeping almost constant contact with at least one herd, and others barely getting a look-in. While they generally drive away any rival males from their territory, they are more tolerant of low-status individuals who show no interest in mating.

Males mark their territory by dropping dung and regularly patrol it on the lookout for potential rivals, thrashing vegetation with their horns as they go. Nonetheless, invitations to sparring bouts are surprisingly civil, with the bull approaching his target with his head held at shoulder level, and then gently nudging him with his horns until he gets a response. A male holding his head down and tucking his tail in is a sign of submission, typically used by younger males towards a dominant bull.

There is no strict breeding season, although births are more common between January and March, in the middle of the wet season. The system is essentially one of harem breeding, and results in the birth of a single calf about eight months later. Births among higher-ranking (older) females tend to occur around the same time, apparently synchronised through scent marks in their urine. 

After birth, as with most antelopes, the mother hides her infant in long grass or similar cover. They remain there for about the first three weeks of life, before slowly integrating with the herd over the next three weeks. The synchronised births allow the calves to remain close together in crèches while they are hiding, and to join the herd together once they are collectively old enough to do so. While they are hiding, the mother remains close by, but not so close as to give away the location of her calf, calling to it only when she fails to see it where she expected... mothers are apparently not so good at remembering exactly where they put their calves as one might think.

Young calves play with their peers, not distinguishing between them based on their sex, presumably as a means of honing their skills and assessing their development. They become sexually mature at about two years, long before they are fully grown or, in the case of males, have their black coat. Females stay with the herd, but males move out around the time of sexual maturity, forming their own small bachelor herds of 2 to 12 individuals. These eventually break up when they reach full physical maturity at around five or six years of age.

Roan antelope

The roan antelope (Hippotragus equinus) once lived across almost the entirety of Africa's savannah zones, north, east, and south of the central jungles, from Senegal, round through Kenya and Uganda to Angola and South Africa. It's no longer quite so widespread, having been eliminated in much of its range, especially in the east, where it has (for example) vanished altogether in Burundi. Nonetheless, it remains a common animal, with no fewer than six subspecies being recognised across its wide range.

In many respects, it is remarkably similar to its close relative. It is about the same size and build as a sable antelope and, like it, has a horse-like mane on its neck. However, the males are not black, and while the name might suggest a mostly dark colour interspersed with white hairs, there is considerable variation between individuals, with some being remarkably pale. There are nonetheless black markings on the face, which are more extensive than on the sable antelope.

They inhabit savannah woodlands, preferring areas with long grass but a reasonable amount of tree cover, both of which also tend to correlate with the amount of available drinking water. Depending exactly where they live, their diet has been recorded to consist of anything from 90 to 100% grass, although we do not have the fine detail that we have with the sable, so it is unclear exactly how similar their diets are. 

Their patterns of social behaviour are also similar, although males seem more inclined to follow the herds about, taking the lead from the oldest female, so long as they can exclude other males from joining them. More commonly, however, they are territorial as the sables are, although they apparently do not scrape the ground with their hooves before leaving droppings, as their relatives do. As one might expect, those in drier areas with less abundant grass tend to range over wider areas than those around river deltas and the like.

One of the few studies conducted on their reproductive habits suggested that female drop to their knees to indicate a lack of interest in mating. Otherwise, the process is much the same, with the males maintaining a harem. Females remain receptive for up to three days, during which time, they have occasionally been seen to engage in lesbian sex, although it's hard to know exactly what that means in a non-human species.

Addax

The closest living relative of the sable and roan antelopes is the addax (Addax nasomaculatus), once found wild across the southern edge of the Sahara, from the Atlantic to the Nile. Now, however, it is virtually extinct, with the only definitively known population inhabiting one small region in central Niger. That population is thought to include fewer than 100 adults, meaning that it is unlikely to be viable in the long term. Reports occasionally come in of sightings elsewhere, notably Chad and Mauritania, but assuming these are accurate, the populations there must be so small that local extinction would be unavoidable.

Fortunately, this excludes those addax living in captivity, of which there are at least 600 in formal breeding programs, and possibly twice that many unrecorded on private ranches in the US. Attempts to reintroduce them to the wild have already begun, although none have yet reached the level to be considered a success. But, while the animal is listed as critically endangered, it's thought that its chances of surviving (although not necessarily flourishing) are actually quite good, with its current tiny population almost certain to increase over the next few decades.

Addax are smaller than sable and roan antelopes, standing around 110 cm (3' 7") at the shoulder, and with even the largest males weighing no more than around 100 kg (220 lbs). They have a pale grey coat, that fades to near white on the underparts, although are black patterns on the face and a small bald patch behind the nostrils. Their most notable feature, however, is their horns, which are present in both sexes, and twist in a wide spiral three or four times along their length.

Perhaps the most desert-adapted of all antelopes, they inhabit some of the most desolate regions on Earth, even venturing into the sand fields while travelling between grazing grounds. Their wide-splayed hooves help with this, giving them purchase even on soft ground. While they mainly eat grass, that's because there is little else where they live, and they will happily consume bushes and shrubs if they come across any. Analysis of their digestive tracts has shown that they retain food in their guts for longer than most other ruminants, partly as a consequence of the slow-fermenting grass that they eat, and partly to absorb as much moisture as they possibly can; addaxes do not need to drink, although they will if they can.

Herds, as inferred largely from captive animals, are small, with between 5 and 20 individuals. They are highly nomadic, roving widely across the desert in search of patches of edible food or following the infrequent rains. During storms and cold nights, they shelter by digging hollows in the sand and hunkering down to wait out the weather. The herds seem to have the same structure as in sable antelopes, with a dominant female leading the way, and a structured hierarchy beneath her. Less is known about how the males behave in the wild, where they can range as they will, but they establish territories when kept in captivity and try to guard harems from rivals.

The single calf is most commonly born in the winter or spring, and spends the first few days of its life hiding in the minimal shelter available. They rejoin the herd more quickly than sable antelope do, at around two weeks of age, living in crèches with others of the same age from then on. 

Bluebuck

There was, however, one other species of hippotragine antelope in recent times. This was the bluebuck (Hippotragus leucophaeus), a close relative of the sable and roan antelopes and generally similar to them in form. It was distinguishable by a slightly smaller size, similar to an addax, and a bluish-grey coat without any of the facial markings seen in the other species. It used to live in South Africa, on the coastal renosterveld, a grassy habitat close to the Cape. At the time, this was grassier than it is now, but the arrival of white colonists eliminated most of the large local herbivores, changing the floral composition of the landscape.

The bluebuck was the first hippotragine species to be scientifically described, in 1766, but it was also the first species of large African mammal to go extinct in historical times. The last individual is thought to have been shot in 1800, a remarkably short time after its discovery, probably due to the population already being small and restricted to a small area when Europeans first arrived. Today, a few specimens remain in museums, although many labelled as such have turned out to be sable or roan.

Given how long ago this was, and how briefly the living animal was known to European naturalists, we know very little of what these animals would have been like, barring their physical appearance. We can assume a similar grass-based diet to their close relatives, based partly on their obvious similarity, and partly on where they are known to have lived. A 2013 study based on skeletal remains going back thousands of years suggested that they were migratory, calving in the winter at the west of their original range, when grass was at its lushest, and then heading east following the summer rains before returning in autumn. Changes in the climate after the end of the Ice Ages rendered this tactic less effective, reducing their population until white colonists delivered the final blow in the 18th century.

Although it was long thought otherwise, genetic studies on the few available remains have shown that the bluebuck was more closely related to the sable than to the roan antelope.

While we know of some fossil species, that brings me to the end of the recent species of "horse-antelope". Next time, I will be taking a first look at another, similarly small, subfamily of antelopes, ones that live in much damper habitats...

[Photos by Bernard DuPont, Charles J. Sharp, and Zachi Evenor, from Wikimedia Commons. Drawing by Joseph Wolf, in the public domain. Cladogram adapted from Bibi, 2013.]