Antilopine Antelopes: Almost-Gazelles of Tibet

Tibetan gazelle

It's often the case that the common name of a type of animal in English does not map directly to a scientific understanding, especially once we add modern genetic discoveries into the mix. So it is with the word "gazelle", which derives from an Arabic word that literally means something like "graceful" or "slender" and is used to refer to a range of relatively slim, fast-running antelopes. 

In a stricter, scientific sense, gazelles would really only include those species closely related to the genus Gazella, short-coated animals, often with dark stripes down the side, and that tend to live in hot deserts or semidesert regions. Even this excludes animals such as springboks, since they are less related to the true gazelles than is, say, the blackbuck. Most true gazelles live in Africa, but there are some in Asia, mostly in the Middle East, but with one reaching as far east as northern China. However, a second group of animals commonly called "gazelles" also lives in Asia, and not somewhere that most Westerners would generally associate with such animals.

While they are usually considered to be members of the same subfamily, these animals are not closely related to the true gazelles, arising from a separate, and possibly much earlier, evolutionary event. These include the Tibetan gazelle (Procapra picticaudata), now sometimes referred to by its native name of "goa" to indicate its non-gazelle-ness. As their name suggests, these live only in the Tibetan-Qinghai Plateau north of the Himalayas. This places virtually all of them in territory claimed by China, although there are also tiny populations just across the Indian border in Ladakh (northeastern Kashmir) in the west and Sikkim in the east.

Although they are about the same size as African gazelles, and have a similarly slim build, there are some distinctive differences. For one thing, female Tibetan gazelles never have horns, even the small ones found in female true gazelles. Perhaps more significantly, they entirely lack the large pitted scent glands in front of the eyes that are typical of true gazelles and have smaller scent glands on the feet than they do. They, and their close relatives, have a much blander coat pattern, lacking side stripes or facial markings, and their tails are extremely short. 

Perhaps surprisingly, given the climate, they do not have an undercoat, although their fur does become thicker and denser during the winter, and the hairless patch on the nose is almost entirely absent. Their colour is a uniform grizzled tan, except for a white underbelly and a very prominent white heart-shaped patch on the rump, which probably helps signal others when they are fleeing predators such as wolves or snow leopards. Males and females would be almost indistinguishable were it not for the fact that only the former have horns. These curve backwards, barely diverging, and have ridges along most of their length; they can reach up to 27 cm (11 inches). The hooves are short and wide, which may help them walk on soft springy surfaces in wetlands.

Their home, of course, lies within the great rainshadow of central Asia, but, unlike their namesakes elsewhere, Tibetan gazelles cannot be said to be desert animals. Instead, they inhabit alpine meadows above the treeline, often close to rivers or other water sources. At least 3,000 metres (9,800 feet) above sea level, the region is a mix of high-altitude plains and steeper hills; this, it might be noted, is high enough to give an unprepared human altitude sickness, even if they are reasonably fit. While the males tend to stay in comparatively low-lying areas to maintain their breeding territories, females often head to even higher altitudes to give birth during the summer, reaching as high as 5,750 metres (18,900 feet) in the more mountainous margins - perhaps because predators are rarer so high up. 

In these regions, we might suppose that Tibetan gazelles feed mainly on grass, but, in fact, this is a relatively minor part of their diet, perhaps about a sixth of their intake. Instead, about half of their diet consists of wild legumes such as locoweed, although more so in the summer growing season than at other times. The remainder consists of various herbs and low-lying shrubs such as Pamir winterfat and Leontopodium (a relative of edelweiss). 

Reports of the herding habits of Tibetan gazelles vary widely, with some suggesting they are almost solitary and others that they gather in herds of 50 or more individuals. It's most likely that they tend to be self-sufficient, with the only permanent associations being between a mother and her young children. But females, in particular, may cluster together temporarily for protection or access to a shared food resource; thus groups of up to ten females are commonly seen together, while males are more likely to remain solitary outside of the breeding season.

That breeding season takes place in the winter, primarily in January. In December, males prepare by vigorously fighting with their horns to establish or maintain territories, which they then mark by scraping shallow pits in their ground with their hooves and urinating in them to focus their scent. By the time January comes around, they seem to just stand around looking hopeful rather than performing any particular display. Pregnancy lasts six months, so that the young are born in the height of summer.

Illegal hunting and the use of prime sites by farmers for raising livestock have both contributed to a population decline in recent decades, although the total population may remain as high as 100,000 and they are not formally considered a threatened species. Analysis of the genetic variation amongst their populations suggests that they have been through bottlenecks in the distant past, probably retreating to three distinct refugia during the Ice Ages when glaciers covered much of their homeland.

Mongolian gazelle

The Mongolian gazelle (Procapra gutturosa) or "dzeren" is far more numerous and apparently not suffering any long-term population decline. Although it is locally endangered in China and no longer occupies as large an area as it did centuries ago (as shown by cliff drawings dating back to 500 BC far to the west of its current range), it's still doing remarkably well overall and is probably the most common wild hoofed mammal in the region. Today, it lives primarily in eastern Mongolia, and just into the neighbouring border regions of both China and Russia. As the world warms, there is some evidence it is actually extending its range northward, further into eastern Siberia.

Physically, the Mongolian gazelle is significantly larger and stockier than its Tibetan relative, with a shoulder height averaging around 70 cm (2' 4") rather than 60 cm (2 feet) and, at 30 kg (66 lbs), weighing about twice as much. Males are noticeably larger than females, with horn no longer than in the Tibetan species, lacking the clear backwards sweep and turning slightly inwards at the tip. The scent glands in front of the eyes are larger, although still very small compared with those in true gazelles, and lacking the deep pit in the skull to hold them that those species possess. The coat is yellowish-tan, with the same markings as in the Tibetan gazelle, although these are fainter and less clearly demarcated.

Perhaps the most significant difference, however, is the habitat they prefer; it's likely the differing specialisations required for this that first split the ancestors of the two species apart just over 3 million years ago. Mongolian gazelles are very much plains-dwelling animals, and they more closely resemble the true gazelles in that these plains are generally arid semidesert grassland. Since they actively avoid hilly terrain, they also never venture above about 1,000 metres (3,250 feet)... so they don't need to be adapted to low oxygen conditions.

The diet is also different, with a much higher proportion of grass, notably feather grass and wild rye, which can provide over half of their food during the winter months. Although grass remains important, they do eat more widely in the summer, including sagebrush and pea shrub; they have also been reported to dig up wild onions with their hooves. 

Unlike most other antelopes, Mongolian gazelles are nomadic, travelling up to 80 km (50 miles) per day, and capable of running at speeds of 65 kph (40 mph) for up to 15 minutes at a time. Over the course of a year, they can wander across areas of 14,000 to 32,000 km² (5,500 to 12,500 square miles). Despite this, they don't have specific migratory routes, simply wandering as weather and habitat suitability dictate. It used to be thought that females returned to their places of birth to raise their own young, but it turns out this isn't the case - females are found in the same places during the birthing season year after year, but they aren't the same animals, just new mothers finding the same spot suitable.

Mongolian gazelles are naturally gregarious, living in groups of up to a dozen or so individuals that frequently aggregate to create much larger herds that can reach thousands of members. The largest such "mega-herd" so far recorded was in 2007, when only one relatively small area of eastern Mongolia received enough summer rainfall for good plant growth - estimates were that the herd in that year reached a whopping 200,000 members.

The only times that they stop wandering are the winter breeding season and (for females) just after they have given birth. In winter, males establish territories, driving off rivals and advertising for mates with loud and deep bellows. These can be produced because the larynx of male Mongolian gazelles is exceptionally large, twice the size of that of females, and is actively pulled downwards to increase the vocal tract length by 30% when they call. The internal structure is also unusual, with large and tough vocal cords similar to those of roaring cats, supported by a fibroelastic pad described as resembling a cymbal and that is absent in females. Additional sacs in the lower portion of the larynx may also enhance the male's ability to produce loud low-pitched sounds. Dangling from the throat, and with long hairs like a beard, the visible bulge all this produces looks uncomfortable, but it's clearly worth it for the mating opportunities.

Pregnancy lasts about seven months, but females evidently have some control over its exact length because all of those in a given area synchronise their births to within ten days of one another. This may help them take advantage of brief spells of good weather and, in fact, the survival rate of calves seems to be unusually high, perhaps aided by the fact that they can run at 40 kph (25 mph) within two days of being born. Given that the overall population seems to have crashed multiple times in the past, whether due to bad weather or disease outbreaks, this is probably part of what enabled them to recover so quickly.

Przewalski's gazelle

The third and final species of this little grouping is Przewalski's gazelle (Procapra przewalskii). First described by Russian explorer Nikolay Przhevalsky in 1888, the scientific name he originally picked for it turned out to have already been taken so it had to be renamed by somebody else three years later - giving the unusual opportunity to name the animal after the author of the original description, albeit under a more Latinate spelling of his name. 

Once thought to be a subspecies of the Tibetan gazelle, but actually more closely related to the Mongolian one, it is vastly less common than either, living only on the shoreline of Qinghai Lake and the nearby hills. This is the largest lake in China but it's hardly immense (about the size of Lake Manitoba in Canada) and the total estimated range for the species is no more than 250 km². Once widespread, the surviving population was estimated at around 1,600 in 2012, although it had been just 200 in the 1980s, so at least it's moving in the right direction. 

Although not by enough for it not to be internationally listed as an endangered species.

They are slightly larger than the Tibetan gazelle but otherwise have a similar appearance although, unlike that species, males are larger than females, the coat is a more sandy colour, and the horns turn in towards one another at the tips, especially in younger males.

Although it's not necessarily the habitat that they would prefer, the landscape around Qinghai Lake is hilly and occupies a boundary between areas of open grassland and true sandy desert. Here, it eats a diet high in grass, accompanied by sagebrush and other plants similar to those eaten by its relatives. The altitude of the lake is around 3,200 metres (10,700 feet), similar to the lower terrain inhabited by the Tibetan gazelle. On the other hand, while they do climb the nearby hills, we have no idea whether they would climb to higher altitudes if there were any mountains nearby in which to do so. When disturbed, they are likely to flee into the barren desert where, presumably, other animals are reluctant to follow them. 

Like the Tibetan gazelle, Przewalski's species females live in small groups, only rarely exceeding eight individuals, while males are more likely to be solitary or in groups of two or three. Pzewalski himself, however, noted herds of up to 40, so it's likely that this is another effect of their small modern population. Decision-making within the herds has been described as "partially democratic" requiring a near-majority of adults to move to new pastures or whatever... but matters may well have been different when the herds were larger and consensus harder to determine. 

As in the Mongolian gazelles, Przewalski's are polygynous, at least by inclination, with the male displaying to attract as many females as possible. Once he has found one that is suitably receptive, he courts her by making the unusual display of standing on his hind legs and prancing towards her, mating in a vertical posture with his forelegs tucked up against his chest. This resembles the mating behaviour of gerenuks, but does not involve any thrusting and only one penetration per attempt. One study recorded it as being remarkably ineffective, with the male only achieving success about 8% of the time; one can only presume they try again later if the female hasn't gotten bored and wandered off by then.

The exact placement of these three species is uncertain, although it's clear that they have a long history distinct from the true gazelles. But there are other antilopines that, according to most modern studies, split off even earlier, taking their own, entirely different, evolutionary path. Next time, I will be turning to look at some of those animals and why they, at least, can't really be called "gazelles" at all.

[Photos by Ashwin Visnawathan and Anna Vasilchenko, from Wikimedia Commons. Drawing by Philip Sclater, in the public domain. Cladogram adapted from Guo et al. 2019.]