Sunday 21 April 2024

Antelopine Antelopes: The Gazelles of Asia

Arabian gazelles
I suspect that, on the whole, westerners associate gazelles with Africa. We think of the ones we see in wildlife documentaries, being pursued by cheetahs or leopards across the plains of the Serengeti or similar places. However, the most current theory suggests that they may have originated in Asia and various species survive on both continents today, having split apart around 2 or 3 million years ago at or shortly before, the start of the Ice Ages.

How many species that might be is still a matter of debate, and much of it centres on what's probably the first part of Asia you'd think of to look for desert-dwelling animals: the Middle East. For much of the 20th century, there were generally regarded as being two species living here, not counting one or two then thought to be extinct. And then, well, all that fell apart for reasons I wrote about on this blog back in 2013.

So what's happened in the ten years since? I'd be exaggerating if I said that things had been settled to the satisfaction of absolutely everyone but the Antelope Specialist Group of the IUCN, who are about as definitive as you're going to get on this subject, currently recognise three. One of these is the one I wrote about in that blog post, that "southern group" of mountain gazelles that ended up with the name of one of the supposedly extinct species: the Arabian gazelle (Gazella arabica).

As currently defined, the Arabian gazelle lives in scattered groups across the Arabian peninsula, with the largest population thought to be along the north coast of Oman, an area that includes a significant nature reserve. Others live in the United Arab Emirates and in the mountains of western Saudi Arabia and (possibly) Yemen close to the Red Sea. Further north, there may also be a small and isolated population in the Arava - the border region between Israel and Jordan south of the Dead Sea - and probably a few places in northern Saudi Arabia. 

They have a somewhat variable coat colour, from light to dark brown, but usually with clear black stripes along the flanks, and always with the clear black-and-white facial markings common to most gazelles. They inhabit both mountainous regions and coastal plains in areas that are probably best described as semi-desert. They are active mainly at dawn and dusk, avoiding the full heat of the day, especially in summer and taking shelter where they can among thorn bushes or in rocky ravines.

The thorn bushes are also their primary source of food, as they are for many gazelles. However, they eat other plants too; on the Farasan Islands in the Red Sea, wild jute and capers have been recorded as a major food source, while grass seems something of a last resort. In addition to avoiding the heat, being active at dawn also allows them to obtain water by eating leaves when there is still some morning dew on them. They have also been reported to eat milkweed, which is poisonous to most animals but which contains plentiful liquid sap.

Sand gazelle
They live in small groups and are often solitary, preferring to stay away from areas with human activity. Analyses of the way they leave dung piles as markers show that while the males may be territorial, the females are not, choosing to scent mark the centres of their home ranges rather than the boundaries. They can apparently breed at any time of year, but most births are in the spring, with a second peak in the autumn, even though fawns born in the autumn are less likely to survive, presumably because of the (relatively) cold winter nights.

The sand gazelle (Gazella marica) is another newly-recognised species, having been promoted from the subspecies I described it as in my 2013 post when genetic evidence rendered that position untenable. As the name suggests, it too, lives in Arabia, once inhabiting the whole of the peninsula, but now restricted to a few smaller places away from humans or in nature reserves. A population also survives further north in Jordan and Syria, with a few probably still found in central Iraq. In the extreme north, they are found in border regions of southern Turkey, where they were recently reintroduced.

Whether or not it was a subspecies of something else, it had at least always been clear that sand gazelles were a different species to what we now call the Arabian gazelle. They are much paler, often lacking the black stripe down the side altogether, and with more white markings on the face. While the horns of females are shorter and straighter than those of males, this is not to the same extent as in Arabian gazelles. Furthermore, while the Arabian gazelle is often found in rugged, even mountainous, terrain, sand gazelles avoid such places, being found in the true desert on flat plains dominated by sand dunes or stretches of gravel and open basalt. 

These are, of course, not places with dense vegetation cover and even the thornbushes that other gazelles favour are not common here. Nonetheless, sand gazelles are not found in totally barren areas, even if the food they do eat is often sparsely distributed. Over half of their diet consists of grass but, during the driest times of the year, when grass is scarce they will readily switch to eating other plants. (This is not apparent from their tooth wear patterns, which imply they eat almost nothing but tough, abrasive grass - probably because everything's so dusty where they live that even regular leaves are covered in grit that wears their teeth down). In Arabia, the most common non-grass food items include heliotrope, bindweed, amaranth, and rock roses; they have also been observed feeding on desert melons, which are strongly bitter but a good source of water.

Sand gazelles are also well adapted to heat, as they have to be given that parts of their range regularly exceed 40°C (104°F) in the summer. This is partly achieved by a naturally high body temperature, but also by their ability to raise that even higher in hot conditions without ill effects. Even if they don't get the opportunity to drink, so long as they have water in their food they can survive for extended periods in the Arabian summer without any signs of dehydration.

Compared with Arabian gazelles, they are sociable animals, often travelling in groups of over a dozen individuals in the winter but splitting up into smaller groups with a single male during the summer. The rut takes place in the autumn, with young born in the spring; there is some suggestion that twins are more common than is usually the case for antelopes.

Arabian gazelles, as now understood, were formerly considered to be southern populations of the mountain gazelle (Gazella gazella) while the northern populations still retain their original name. They survive - just about - in Israel and the Golan Heights and probably in some parts of Jordan. None have been seen in Syria since the 1970s or in the Sinai since the 1930s while their status in Lebanon and southern Turkey are unclear - if they survive there at all, they are certainly rare. 

Mountain gazelle

Like the Arabian gazelle, they are common in hilly and mountainous terrain and they prefer places with steep slopes in which to shelter. Even so, they can also be found on high, flat, plateaus and even the coastal plain. They eat grass in winter, but switch to leafy browse in the summer, with the leaves and fruit of "lotus trees" being particularly favoured. Females live groups, reported to be of four to six individuals in modern times in the Mount Carmel area, but of up to 40 in the past. Both sexes are territorial, but the males, which are primarily solitary, are especially so, marking their territories with dung piles that can be a metre (3 feet) or so across. Breeding takes place later than in related species, with the young being born between April and June.

The mountain gazelle has been listed as an endangered species since 2003 - although, due to the changes in taxonomy, this was originally as an endangered subspecies. Once far more numerous, the rapidly increasing human population in Israel over the course of the 20th century has left fewer and fewer places where they can survive. By the 1990s, around 10,000 were thought to be left, and since then the decline has rapidly accelerated with the population at least halving over the last 20 years, and potentially being as low as 2,500 today. Although they are legally protected, poaching is rife, and the rapid expansion of roads both results in either their death from car collisions or, for those cautious enough to avoid that, isolates them from one another and reduces their genetic diversity.

Goitred gazelle
The sand gazelle, on the other hand, had previously been considered to belong to a different species, the goitred gazelle (Gazella subgutturosa). This is another desert and semi-desert dweller, living across many of the more arid parts of Asia from western Iraq, through Iran, across Central Asia and into the Gobi Desert in Mongolia and northern China. They are far more common in the eastern parts of their range, with the Iranian subspecies being restricted to a few nature reserves and an even smaller number remaining in Azerbaijan (some of which were recently reintroduced to neighbouring Georgia where the native population had died out). They were once found in the Chagai Desert of western Pakistan, but have all but vanished there in recent years. Quite where in Iraq it is replaced by the sand gazelle is unclear; the two species can interbreed and there is probably some blurring between the two.

They have paler facial markings than other gazelles, at least as adults, with only a faint brown stripe from the eyes to the nose, and the rest of the face white. Unlike other gazelles, normally only the males have horns, although a few females develop short stubs. Another distinctive feature is that the males have a greatly enlarged larynx in the mating season, allowing them to make particularly loud mating calls; it is from this that they get both their common and scientific names.

The great bulk of their diet consists of shrubs, although grass is also eaten throughout the year. The overall range of their diet is broad, but they have a preference for succulents when the weather is dry, since these can provide them with much-needed water. Their habitat requirements are similarly broad, with almost any arid environment acceptable and they have been found at altitudes up to 2,700 metres (9,000 feet). 

Although, in practice, groups tend to be small with fewer than ten adults each, although some herds have been reported with nearly a hundred members. Regardless, the structure of the herds changes throughout the year. During the winter rut, females dominate, with the males moving apart so that they can claim territories and fend off rivals, while more mixed-sex groups are common at other times. 

The goitred gazelle is not the only species of gazelle in Iran, because it shares some of its range with the chinkara or Indian gazelle (Gazella bennettii). Indeed, while they do not normally interbreed, they are at least capable of doing so some of the time, since some Iranian chinkara have been shown to have DNA from goitred ancestors; this is probably a rare event, akin to the very occasional fertile mule.

Chinkara
The chinkara also prefers flatter, drier areas than the goitred gazelle, and is likely much less tolerant of the cold - it snows in winter in the northern parts of the latter's range. Iran is merely the westernmost extent of the chinkara's range and only around a thousand or so are left there. They are also rare in Pakistan, and possibly vanished, or nearly so, from southern Afganistan, but they remain relatively common in northern and central India, making them by far the most numerous of any of the Asian gazelle species and the only one not to be considered to be under immediate human threat. This may be aided by the fact that, while the dense human population of India is undoubtedly a problem for the species, in some places, such as the Thar Desert of Rajasthan, the animal may be protected by local  religious communities.

The chinkara inhabits desert and semi-desert plains, often venturing into rocky hills where it can take shelter in steep ravines and, especially in the Deccan of central India, even inhabiting scrubby forests on the margins of denser jungles. Their food consists primarily of shrubs, with wild jujube and capers being the most common in Rajasthan and desert saltwort in Iran. They have also been noted to eat milkweed, a poisonous plant that would harm domestic cattle.

Physically, they are similar in size to other Asian gazelles, which is to say somewhat smaller than most of the African species, standing about 60 cm (2 feet) tall at the shoulder. Their horns are almost straight with unusually prominent rings along their length, and are nearly as impressive in females as males. They are paler than many other gazelles, with only faint dark markings on the face, and the dark stripe along the flank of most other species barely visible at best, and often absent altogether.

They live in small groups, as their related species do, with five or six adults per hers being the most common. Groups are smallest in Iran, which could be a subspecies difference, but is more likely to be due to their comparative rarity there. In India, herds with as many as 26 adults have been seen, although these are uncommon; larger groupings are probably temporary aggregations near some suitable food source rather than a true herd. Births are most common in the spring, but can also occur in autumn and it is assumed that they must therefore have two breeding seasons each year.

I mentioned at the top of this post that there were thought to be "one or two" recently extinct species of gazelle in Asia. The uncertain one was the Arabian gazelle, now known to be alive, at least under its current definition. The other is the Queen of Sheba's gazelle (Gazella bilkis) described on the basis of five dead specimens collected in the Yemen in 1951. It has not been seen since, despite active attempts to do so, and is widely regarded as extinct. For that matter, absent any genetic tests on the specimens in question, it isn't entirely certain that it isn't just another subspecies of Arabian gazelle.

While the above are the only 'true' gazelles in Asia, Africa is home to rather more species. I have already covered most of them, but a few remain that are distinct enough to be placed in their own genus, first named in the 19th century before being placed back in Gazella, then resurrected in recent decades to fit with genetic data. It is to these last few African gazelles that I will turn next time.

[Photos by Charles Sharp (first two images), "Bassem 18", El┼čad Ibrahimov, and Mike Prince. Cladogram adapted from Bibi 2013 and Lerp et al. 2013.]

2 comments:

  1. Your cladogram *does* show goitred and chinkara as one another 's closest relatives.

    ReplyDelete
    Replies
    1. Thanks! I can't recall what it was I meant to say, so I've just deleted that line...

      Delete