Antilopine Antelopes: Dik-diks

Kirk's dik-dik

The "antilopine" antelopes are, as their name might suggest, mostly typical examples of their kind. I suspect that when many people think of antelopes in general, gazelles and springbok are among the first to come to mind (although, to be fair, so might say, impalas). Traditionally, the antilopines have been divided into two main groups: the gazelle-like antelopes and the dwarf antelopes, with the latter surely being the less familiar to those of us living outside of Africa. Both groups have at least some species that don't fit the "typical" image of the subfamily. For the gazelle-like animals, that's probably the gerenuk and its relative, the dibatag.

Among the dwarf antelopes, we have the dik-diks.

While some researchers subdivide them further, four species of dik-dik are widely recognised, at least three of which are reasonably common within their respective homelands. This may partly be because they are too small to be worth hunting for meat - although, inevitably. this still happens from time to time. 

The most widespread, numerous, and well-studied of the species is Kirk's dik-dik (Madoqua kirkii). This is named for Scottish explorer and naturalist John Kirk, who collected the initial specimen described by Albert Günther in 1880. They live in two quite distinct areas of Africa, in Kenya and Tanzania on the east coast and Namibia and Angola on the west. The two populations are genetically distinct, and are among the strongest candidates for being raised to separate species status - indeed, there is a good chance that Kirk's dik-dik could represent as many as four different species. 

Considering them together, as they usually are for the time being, Kirk's species is the largest of the dik-diks, standing 38 to 43 cm (15 to 17 inches) in height at the shoulder, and weighing just 5 kg (11 lbs) on average. It is a slender antelope, with greyish hair fading to chestnut on the flanks and legs. Males have small horns, but the females are noticeably larger overall, in contrast to the usual pattern among mammals. Distinctive features include an elongated snout with an inflatable nose, an almost non-existent tail, and a prominent tuft of hair sticking up from the top of the head. The word "dik-dik" comes from the sounds that they make.

They live in semi-arid shrubland and savannah with plentiful thickets of thornbushes and similar plants. They eat little, if any, grass, being rather fussy eaters nibbling only the best leaves and buds from plants, sometimes spitting out those they don't fancy. Like many other antelopes in dry environments, they do not need to drink, taking in enough water from dew and sap in the vegetation that they eat - even when waterholes are available, they rarely visit them, even in the dry season. 

The enlarged nasal cavities and unusually small nostrils are an adaptation to the hot and dry environment, cooling the blood as it passes through the lining and retaining moisture from expired air - dik-diks also lick their own noses to gather any dew that may have formed there. Other adaptations include the ability to produce extremely concentrated urine and unusually dry dung; their kidneys may be more efficient than those of any other mammals except for a few kinds of desert rodent. They also have fewer sweat glands even than other desert-dwelling antelopes, cooling themselves down by panting through their nose when they must.

Kirk's dik-diks become notably uncomfortable below about 25°C (77°F), but don't even start to pant until the temperature reaches at least 40°C (105°F), an unusually high level for a mammal. Even so, while generally diurnal, they keep cool by resting during the hottest times of the day and carefully orienting their bodies to make the most of the local wind direction.

Another unusual feature of the species, and of dik-diks in general, is their monogamy. They live in mated pairs, rather than herds, perhaps separating during the day to forage, but cuddling up together at night. The pair marks their territory with dung piles, which can be impressively large considering the small size of the animals - they can easily reach 2 metres (6' 6") across and 10 cm (4 inches) in height. Unlike most other antilopines, they lack scent glands on their feet, although they do have the large glands in front of their eyes typical of most antilopines. 

In other monogamous ungulates, we would expect some degree of infidelity, but paternity testing suggests this is extremely rare in dik-diks. This seems to be largely down to the female, who will not entertain strange males, possibly because she doesn't want them to start a fight with her own partner. Should her partner die, she will usually find a new one within two or three days, but males in a similar situation apparently take a lot longer, so she's probably the one calling most of the shots. 

Otherwise, mating appears to be for life, or close to it, despite the fact that males don't seem to help their partners care for their calves - the usual explanation for monogamy in mammals. Even more unusually, when a female is forced to find a new partner, he makes no effort to kill any existing calf she might have, as males in other mammal species generally do. (It may, of course, be relevant that she's quite a bit bigger than he is).

Courtship rituals among dik-diks are fairly minimal, presumably because if you're monogamous anyway, there isn't much need for anything elaborate. Young are born mostly in February and March, and hide in thickets for the first three weeks of life. Females leave home at seven months, but males wait at least eleven, and may even stay with their mother for two-and-a-half years if they have difficulty finding a willing partner.

Günther's dik-dik

Günther's dik-dik (Madoqua guentheri) is named for the zoologist who first described Kirk's species, and is both the second largest and the second most widespread of the four generally acknowledged species. It lives in Somalia, southern Ethiopia, northern Kenya, and neighbouring parts of Uganda and South Sudan and is even more desert-adapted than Kirk's species. While the latter prefers semi-arid scrubland, Günther's species can inhabit more truly arid environments and rocky lava plains; where the two species live side-by-side in Kenya, it prospers in the driest of habitats, leaving those with more water to its neighbour.

Males stand about 34 cm (13 inches) high at the shoulder, and females 36 cm (14 inches), with the latter being about 10% heavier. The crest of erect hair on the head is darker than that of Kirk's species, being tinged with black. In many other respects, they are similar to the larger species, and have much the same diet, focussing on acacia and bushwillow shrubs.

A significant difference, however, lies in the nose. For one, it's even larger than in Kirk's species, with the nasal bones that normally form the bridge of the nose exceptionally short to allow room for a long, fleshy, and muscular roof. Unlike that in other dik-diks, however, this is much more flexible, allowing the animal to move it about like a tapir's proboscis. The main function, however, appears to be to allow the dik-dik to use its nose-muscles like bellows, increasing the efficiency of panting when it needs to cool down. 

Their monogamous lifestyle is also similar to that of Kirk's dik-dik. Mated pairs jointly mark their territory, using dung piles and scent marks from the glands in front of their eyes. At least in the Omo National Park in Ethiopia, each pair occupies between 4 and 14 hectares (10-35 acres) and is spaced 300 to 600 metres (330-660 yards) apart. The males defend these territories from rival pairs, stamping and pretend jabbing with their horns with physical fighting as a last resort.

Salt's dik-dik

The first dik-dik to be described scientifically was, however, Salt's dik-dik (Madoqua saltiana) named in 1816 for the then British Consul General in Egypt. Despite this, they are not, in fact, found in Egypt, instead living further south in the Horn of Africa, in Somalia, Djibouti, and eastern Ethiopia. Although similar in shoulder height to Günther's dik-dik, they have a lighter build, with even the females weighing no more than about 3 kg (6½ lbs). They also have a brighter colour, with distinct reddish hair on the flanks and legs and some ginger flecks on the back. The nose is larger than is usual for antelopes, but much less so than in its immediate relatives.

They are less studied than the other two species, and while they seem to have similar habits, we know little detailed information about them. They live in similar dry scrubland, fleeing into the bushes when disturbed. Their favoured foods are the leaves and shoots acacia thornbushes and Egyptian balsam, with grass and herbs forming less than 10% of their diet. Like other small ruminants, they retain food in their stomachs for longer than large species, presumably digesting it more thoroughly, as well as having a low metabolic rate for their size.

The remaining species is both the smallest and the most obscure. The silver dik-dik (Madoqua piacentinii) was first identified as a distinct species from a small population living along the southern coast of Somalia. Since then, a few have been spotted in a single valley in Ethiopia, but it is unclear to what extent they might also live in the surrounding area or in the territory between their two known ranges. They stand about 30 cm (12 inches) high, with a coat that is, as their name would suggest, silvery in colour along the back and they have grey, rather than reddish, fur on the forehead. In other respects, they are hard to distinguish from Salt's dik-dik.

That brings me almost to the end of the antilopine antelopes. I said at the start of this post that the antilopines were traditionally divided into two "main groups". Although the traditional view turns out to be oversimplified in the light of modern genetic evidence, it did, however, include one additional species that fit into neither group. So it is with that, another highly distinctive animal, that I will conclude next month...

[Photos by Yathin SK, Summer J. Smentek, and Tony King. Cladogram adapted from Calamari et al. 2021.]