Sunday 6 November 2016

Bovines: Bushbuck and More

Of all the many kinds of antelope found in Africa, the one that is most widespread is the bushbuck (Tragelaphus scriptus). Bushbuck are essentially found throughout the whole of sub-Saharan Africa outside of the densest parts of the Congo jungles, the Kalahari Desert, and the drier parts of the veldt and the Horn of Africa. That's a huge range; everywhere from Senegal to Angola, and from Djibouti to the Cape.

Bushbuck are the smallest of the African bovines, sufficiently so that any resemblance to cows beyond the basics true of all antelopes (horns, cloven hooves, and so on) is quite absent. Specifically, they stand 60 to 100 cm (2' to 3'3") tall at the shoulder, with the males slightly taller, and much more heavily built, than the females. They do, however, much more closely resemble their larger immediate kin, such as bongos, having a somewhat similar coat colour, and the same twisted horns that make about a single turn along their length. Unlike in bongos, however, the horns are only found in the males - a feature shared with another close relative, the swamp-dwelling sitatunga.

Despite their wide range, bushbuck do have some habitat preferences, tending to live near forest edges, in open woodland, and on the fringes of more open grassland. They are usually found near water, presumably because the vegetation in such places is more lush, since they don't seem to need a huge amount to drink. They are considered browsing animals, another feature that distinguishes them from the larger, more cow-like, bovines, and the bulk of their diet consists of shrubs, herbs, and the like, with only a small quantity of grass to round things out. The wide range of plants they are able to eat means that the aren't really affected as the seasons change, with their diet not needing to change much over the course of a year, and also likely explains their wide distribution across the continent.

Bushbuck rest both during the heat of the day and during the night, alternating cycles of eating with standing around chewing the cud, as many ruminants do. Some early studies, back in the 1970s, seemed to suggest that they were primarily nocturnal, doing much of their feeding around midnight, but more recent ones indicate that there is little, if any, such pattern, although they may move around more between different feeding sites, at dusk and dawn.

Apart from mothers with their young, bushbuck are normally seen alone, and they are generally thought to be the least social of all the spiral-horned antelopes. On the other hand, they don't actively avoid one another, so that sightings of adult pairs are not really uncommon - it's just unlikely that they are any more than a temporary coincidence if they aren't ready to mate. Females wander over a smaller range of territory than males do, but, being smaller, this is probably just because they require less food, and there is no evidence that they try to keep rivals out of "their" patch. They also move shorter distances to find their own home after leaving their mothers, with the result that female bushbuck in a given area are likely to be related to one another - something quite common among mammals in general.

The evidence for males defending territory is rather more equivocal. They certainly don't seem to do it much, since their home ranges overlap with one another, and only tend to get aggressive if there's a female in heat around, but a few studies suggest that older males, at least, tend to avoid too much competition with one another outside of the breeding season, and that they scent mark the very cores of their territories, just not the boundaries as other mammals might. These scent marks are made using glands on the animal's faces, but bushbuck also tend to defecate at particular locations, something that would often indicate territorial marking. In their case, however, the pattern in which they do it suggests almost the opposite - they're probably signalling their reproductive status to members of the opposite sex.

This is important particularly because there is no defined breeding season, so that females may come into heat at any time. Since there are no herds or other long-lasting social groups, it's up to the male to find receptive females as and when the time comes. Older males seem to have an advantage here, being able to remain in broadly the same place, and know the location of all the defecation sites of nearby females. Younger males travel further, and often get to the females first, but have to rely more on luck; they can, of course, also be driven off by larger and more aggressive males if both arrive at the same time. Interestingly, at least some males seem to help defend their calves, despite not being as regularly at their side as their mothers are.

At least twenty different subspecies of bushbuck have been named over the years, as one might expect, given their geographic range. It's unclear how many of these are real, but a genetic analysis in 2008 showed something more surprising: while many bushbuck are, as expected, closely related to bongos and sitatunga, many of those in the north are actually related to an entirely different antelope, the nyala. The separation between these two groups means that they must be different species, and, since the original specimen that Peter Pallas used to describe the bushbuck in 1766 happens to be the nyala-relative, it's the others that get a new species name, Tragelaphus sylvaticus. What the common name of this animal should be has still not being firmly settled, but the local name "imbabala" is one option, and its the one found in eastern and southern Africa, from the Ethiopian highlands to the Cape. [Update: a more recent study, using a larger DNA sample, has thrown doubt on this, arguing that hybridisation between one population of bushbuck and a now-extinct species related to the nyala may explain why the two populations appear to be less related than they really are.]

As for the nyala (Tragelaphus angasii) itself, this is a more medium-sized antelope, and one with the greatest differences in appearance between males and females of any of its kin. Males stand 100 to 120cm (3'3" to 4') at the shoulder, and have a shaggy grey coat with the same narrow white stripes found on other spiral-horned antelopes. Their horns are long, twisted, and somewhat lyre-shaped, similar to those of bongo. Females, on the other hand, are only 80 to 100 cm (2'7" to 3'3") tall, have a short, reddish, striped coat, and no horns. The males, of course, are also bulkier and more muscular, weighing almost twice as much as the typical female.

Nyalas live in Mozambique and in neighbouring areas of other countries from Malawi and Zambia to South Africa. They inhabit wooded savannah country, and are less dependent on water than bushbuck, often living several miles from the nearest water source, and evidently able to survive without drinking for some time. They are browsers, albeit with a higher proportion of grass in their diet than bushbuck, especially during the rainy season when it is at its most lush. Even within the same area, males and females tend to have different diets, with the males going more for shrubs, and the females more for herbs, presumably because of differences in their nutritional requirements, and to ensure that they do not compete with one another for food.

Although they are not truly herd animals, and are often seen alone, nyala do gather together into temporary groups of as many as thirty individuals. Most often these are females, many of which continue to have some bond with their adult offspring, and males are much more likely to be on their own, or in very small groups of two or three. While avoiding the worst of the midday sun, nyala are active during the day when they get the chance, but are perfectly capable of switching to a more nocturnal lifestyle where humans are a threat.

Breeding takes place throughout the year, although in some places it may be more common at times of the year when the resulting birth lines up with the beginning of the rainy season. Males use their horns to thrash at vegetation, and threaten one another by displaying crests of white hair on their backs, but only rarely use the horns to actually fight one another. Oddly, females are said not to be very attentive mothers, and it is apparently not unusual for larger predators, such as lions, to take young without the mother putting up much of a fight. Presumably, the risk of dying is worse than the cost of having to raise another calf to replace the first one. This is not to say that they ignore their calves altogether, of course, and, as noted, parental bonds seem to last for a long time.

Heading further north, we come to the mountain nyala (Tragelpahus buxtoni), an endangered species now found only in a few protected areas in the mountains of Ethiopia. They closely resemble their more common southerly namesakes, but are larger, and, while the coat is overall less shaggy than in male nyala, male mountain nyala do have a crest of stiff hair running down their back. The horns, which, again, are only found in males, have a much wider and looser spiral, are somewhere between that of true nyala and kudu. Indeed, the initial specimen, which was only described by Richard Lydekker as late as 1910, had previously been thought to be the horns and skin of a greater kudu, rather than a new kind of animal.

Mountain nyala
It was the last entirely new species of large antelope to be discovered from Africa, but, given its remote and tiny homeland, relatively little study seems to have taken place of the animal until the 1960s. More recently still, genetic evidence has shown that, despite their physical similarity, mountain nyala are not close relatives of the true nyala. In consequence of this, alternative names, such as "gedemsa" have been suggested for it, to avoid confusion between the two species, but none of these have as yet widely caught on.

As the name suggests, mountain nyala live at high elevations. For the most part, they inhabit high wooded slopes, between about 1,800 and 3,500 m (5,900 to 11,500 feet) elevation, but they sometimes venture further uphill into more rugged and sparsely vegetated terrain as high as 4,300 m (14,000 feet), especially during the dry season. In particular, more open terrain seems to provide them greater safety - perhaps because they can more easily see potential predators coming - allowing them more time to spend on feeding. It's presumably because of this that a higher proportion of their diet consists of grass than is the case for many other related antelopes.

While temporary associations of over 60 animals have been reported, for the most part, herds only number 7 to 12 individuals, including young. As with true nyala, males tend to live in smaller groups than females, or even live alone, as they get older. Also like nyala, males are not very aggressive towards one another, preferring to establish dominance by attacking nearby vegetation than by actually fighting - although they resort to the latter, and sometimes suffer serious injury as a consequence, if one or the other refuses to back down. The little we know of their breeding habits also suggests some similarity to nyala.

A 2011 study estimated the total mountain nyala population at less than 4,000, restricted as they are to a few, increasingly deforested, mountainsides, and commonly hunted for both their meat and their horns. Most other studies have indicated that numbers could be rather less, and the IUCN's current best guess is that less than 2,500 adults survive, and that numbers are continuing to decline.

With that, we reach the end of the spiral-horned antelopes, the second major group within the bovine subfamily, after the truly cow-like animals themselves. There is, however, a third, much smaller group, consisting of just two species of antelope native, not to Africa, but to Asia. It is there that we will finish our survey of the living species of bovine.

[Photos by Bernard DUPONT, "Kay-africa", and Rod Waddington, from Wikimedia Commons. Cladogram adapted from Bibi 2013 and Stankowich 2009].

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