Wednesday 27 March 2024

Antelopine Antelopes: Gazelles of North Africa

Dorcas gazelle
(Brief note: My internet connection was down for three days over the weekend, which is why this post is delayed from the usual.)

One of the things that most distinguishes gazelles from other kinds of antelope is that they are adapted to dry environments. They don't come much drier than the Sahara so it should be little surprise that gazelles are relatively common here. In fact, the dorcas gazelle (Gazella dorcas) is one of the most widespread of all gazelle species, being found right across the Sahara from the Atlantic to the Red Sea, as well as further south along the Red Sea coast in Eritrea and Djibouti and across the Sinai into extreme southern Israel. In the north, it's largely restricted to the eastern parts of the Mediterranean coast, being absent from northern Algeria, Morocco, and Tunisia.

Given this distribution, it was well-known to the ancients, and was among the first antelopes to become familiar to Europeans. Indeed, the word "dorcas" is the original Greek and Latin word for "antelope" before it became supplanted by what was originally the name of a mythical animal. It was one of the first antelopes to be given a scientific name, in Linnaeus' original 1758 catalogue, where he calls it Capra dorcas - literally "the kind of goat that's an antelope". It was also one of the first species to be assigned to the genus Gazella when Henri de Blainville erected it in 1816, and subsequently chosen as the "type", or defining species, of that genus.

It's the smallest of the gazelles, although not by much, standing 60 cm (2 feet) tall at the shoulder, on average. While they have the usual black stripes on the face seen in other gazelles, the darker bands seen along the flanks of many species are much paler and less distinct against the generally fawn background. It's also one of the most desert-adapted of the gazelles, said to be able to live its entire life without once drinking. How true this is in practice is debatable, since it requires them to obtain water from the food that they eat and that depends on what's available in the desert; dorcas gazelles given only dry food begin to noticeably suffer after 4 days without water in the heat of the summer, although they can manage up to 12 days in cooler weather.

The popular image of the Sahara is a seemingly endless sea of dunes with nary a plant in sight. While some parts do indeed look like this, the dorcas gazelle avoids areas that are too sandy, and is most commonly found in rocky plains and sparsely vegetated areas, often, but not always, in the bottoms of wadis - dried up seasonal riverbeds that hold enough moisture for plants to grow. Here, they feed primarily on acacia thornbushes, although they will eat other leaves or seed pods if they are available, and have been observed rooting up bulbs after the rare rainfalls. Unlike most other antelopes, they often stand on their hind legs while feeding, giving them a better chance to reach high branches.

Dorcas gazelles are active throughout the day in winter, but the intense heat of the Saharan summer makes this impractical even for them, so they switch to being active only around sunrise and sunset. Like many animals, they may even change to a more nocturnal lifestyle when humans are around, simply for their own safety. By preference, they live in small herds of no more than a dozen individuals, consisting of a single adult male, several females and their young; the surplus males generally live alone rather than grouping together. Where the habitat is particularly harsh, however, they live as mated pairs.

They prefer open terrain to places that provide cover, apparently more concerned with the ability to detect predators than with their own visibility. Historically, their main predators were probably lions, leopards, and cheetahs, but these have largely been eliminated from the Sahara region so hyenas are a more common threat today. Like other gazelles, the dorcas species is a fast runner, having been reported to reach 80 km/h (50 mph).

During the September to November breeding season, males become territorial, depositing dung to claim patches of land and deter potential rivals. Birth of the single fawn takes place six months later, taking advantage of whatever limited rainy season there may be. For the first two weeks of life, the fawn remains hidden beneath a bush or (if none are available) a shallow depression in the ground. They are weaned at three months, at which point they rejoin the herd.

Although they are widespread, dorcas gazelles are much less so than they used to be, having once been found further south in the Sahel semi-desert but now restricted to the harsher areas where humans are less likely to be encountered. Even here, their populations are thought to be declining, sufficiently so for them to be considered endangered in some countries. 

Cuvier's gazelle

Northwest of the Sahara rise the Atlas Mountains, home to Cuvier's gazelle (Gazella cuvieri). These are darker animals than the dorcas gazelle, a rich brown in colour with visible stripes on the flanks and a clearly offset pale underbelly. They live along the entire range and its surrounding lowlands, mostly in Algeria and Morocco, but with some population in western Tunisia and the disputed territory of the Western Sahara. 

The Atlas Mountains are a dry, desert or semi-desert habitat, but the terrain here is much rockier and uneven. The gazelles which, like the dorcas species, are declining in number have retreated deeper into the mountains in recent times, avoiding human contact as far as possible. They are more likely to be nocturnal, perhaps as a result of this, spending the day hidden among rocks or bushes on the higher slopes, up to about 2,500 metres (8,200 feet), descending into the valleys at night or around dawn and dusk to feed. In semi-desert regions they may inhabit light woodlands of oak and pine but, at least in the summer, they are more likely to favour north-facing slopes with limited plant cover.

Their diet seems more varied than that of dorcas gazelles, likely because there is simply more to choose from where they live. In true desert regions along the southern flanks of the mountains, they feed primarily on acacia thornbushes, as dorcas gazelles do, but further north they prefer grass and wormwood shrubs. In a reserve in Morocco, on the other hand, they have been reported to feed from oak trees and wild olives in winter and on cypress in summer, as well as on shrubs according to their availability.

Cuvier's gazelle has the same herd structure as the dorcas species, with a single male and a harem of females, but the herds are generally smaller, typically with only four members and (at least in modern times) never more than eight, many of whom are juveniles accompanying their parents. The herds break apart in the spring when the females retreat to cover to give birth and suckle their young until they are old enough to get back together again. Males are solitary during this time of year.

Slender-horned gazelle

If Cuvier's gazelle is a mountain dweller, the slender-horned gazelle (Gazella leptoceros) is almost the opposite, if anything being even more desert-adapted than the dorcas gazelle. It lives in patches across the Sahara from Egypt west of the Nile across to southern Algeria; populations may survive further south in Sudan, Chad, and Niger but this is uncertain. Another common name for the animal is "rhim gazelle", taken from a colloquial term in Libyan and Algerian Arabic.

Slender-horned gazelles live in and around the great ergs of the Sahara - the seas of sand dunes that many people instinctively associate with deserts. This explains their unusually pale coat, which is essentially sand-coloured, although they do have black markings on the face and tail. As their name suggests, their horns are narrow compared with other species, and they also tend to be straighter than those of dorcas gazelles.

Relatively little is known of the species, which typically lives in groups of just two or three adults and feeds on desert grasses and succulent plants in oases and sheltered valleys between the dunes. They are said to feed mainly in the early morning when there is at least some dew on the plants, but observations in the wild are few and far between. They are, as one might expect, highly nomadic, moving long distances across the desert in search of rare food sources. The males are very territorial and can become lethally violent when placed together in captivity.

They have few predators other than man now that cheetahs are extinct in their part of the world. Illegal hunting, however, remains a severe problem for the species and the desperately marginal nature of their habitat and their attempts to avoid nomadic tribes have proved insufficient to protect them this far from any effective law enforcement. It is thought that only a few hundred remain alive, leading to the species being officially classified as endangered.

Speke's gazelle

Speke's gazelle (Gazella spekei) is even more of a mystery. The species is native to the Horn of Africa, being found only in Somalia and, just possibly, some neighbouring parts of Ethiopia. Somalia is, let's face it, not the best place to be doing wild animal research at the moment, so the little we do know comes from animals in captivity which mainly concerns basic anatomy, lifespan, and whether or not we can breed them.

First identified as a distinct species in 1863, Speke's gazelle looks similar to, if on average slightly larger than, the dorcas gazelle, although the dark stripe on the flanks is much more prominent. Another key difference is the fact that it possesses an inflatable nose. All gazelles have large nasal cavities, which help to prevent water loss while breathing out, but here the cavities are sufficiently inflatable that there is some visible ridging on the skin of the snout (although less so than in some other antelopes). This enables the animal to make a loud alarm call, a rapid snort that's said to sound like a gunshot.

Somalia is outside the Sahara, but it is a region of semi-desert with extensive dry grasslands, often dotted with thornbushes and succulent shrubs, so the presumption is that this is what the gazelle normally eats. There are no agreed estimates of their population, although the lack of a functional government in Somalia means that they have no legal protection or nature reserves and their numbers are thought to have crashed over the last 40 years. They have been listed internationally as an endangered species since 2007.

Despite their association with Africa, gazelles are thought to have first evolved in the Middle East in the Late Miocene or Pliocene, probably in open plains, with mountain-dwelling species like Cuvier's gazelle having arisen later. Even today, a perhaps surprising number of gazelle species live in the region, and elsewhere in Asia. It is to those animals that I will be turning next time.

[Photos by "MinoZig", C Burnett, Trisha Shears, and "Thomas", from Wikimedia Commons.]

No comments:

Post a Comment