Saturday, 26 November 2016

Bovines: Blue Bulls and the Smallest Bovine

Male nilgai
The bovine subfamily can be divided into two main evolutionary branches. One consists of the truly cow-like bovines, including such things as bison, buffalo, and yak, alongside the regular domestic animal. The other are the "spiral horned antelopes", African species that, despite being more closely related to cows than (say) gazelles, nonetheless have a generally antelope-like body form. But there are two living species that fit into neither of these branches. They are relatively closely related to one another, and so form a third, much smaller, evolutionary branch (usually given the taxonomic rank of "tribe"). Although generally considered "antelopes", both species are native to Asia, unlike their spiral-horned kin.

The larger, and likely better-known, of the two is the nilgai (Boselaphus tragocamelus). Standing 120 to 140 cm (4' to 4'7") at the shoulder, although they are considered antelopes, there is a somewhat cow-like appearance to them, albeit with a much narrower head. Indeed, the scientific name reflects their somewhat odd form, since it literally translates as "cow-deer goat-camel" (in fairness, the two halves of the name were coined separately, and not used together for over 60 years afterwards). They are found throughout India, and in some neighbouring regions of Pakistan and Nepal. They have also been introduced into South Africa, Italy, Mexico, and Texas; while the Italian population died out in the 1940s, and the South African ones remain confined to their ranches, some of those in North America managed to escape, and can still be found wild in those areas today.

An alternative English name for nilgai is "blue bull", because the males of the species have bluish-grey coats with a few white markings, the largest of which is on the throat. The females, while having the same white markings, are, however, tan-brown in colour, are only about two-thirds the weight of the males, have no horns, and lack the "beard" found on the lower part of the males' throats. Anatomically, one of the features that unites them with other bovines is that the horns possess a sharp keel along one side, making them triangular in cross-section, at least at the base. On the other hand, they possess small, but functional, scent glands in front of the eyes - something found widely among antelopes, sheep, and goats, but which is normally absent in bovines.

Beyond their obvious preference for warm climates, nilgai seem to be fairly adaptable in terms of their habitat, although they prefer open, relatively flat, scrubland terrain where it's available, and they do need standing water to drink from. They'll eat pretty much any plant matter that's around, with the main component of their diet varying based on their location and time of year. In at least some regions, they may help with maintaining forests, because of the number of tree seeds in their dung.

They are also said to be able to survive on relatively poor forage, at least compared with local competitors, such as chital and sambar deer. On the other hand, when food is in short supply, the variability of their diet means that they will compete with a number of other herbivores, including domestic livestock. This, combined with their habit of eating agricultural crops, means that they are often considered a pest in India, something only partially offset by the fact that some Hindus consider them to count as cows, and therefore sacred.

Nilgai are not particularly gregarious; while they may be found in larger, temporary, herds, they are mostly seen in groups of two to three adults, with males and females living apart outside of the breeding season. Left to their own devices, they are most active around dawn and dusk, but they will switch to more nocturnal habits where humans are around, especially if they're going to be feeding on cropland. Indeed, they are generally said to be wary of humans, although this is likely a learned behaviour, since apparently they can be quite tame in those parts of India where they are still considered sacred.

Uniquely among bovines, nilgai deposit piles of dung in specific locations, something that, in most animals, would be seen as marking out a territory. While nilgai don't seem territorial enough for this to be likely, it's evidently communication of some kind, and, with the piles often more than 3 metres (9 feet) across, and added to every three days on average, they're hard to miss.

Even during the breeding season, males and females tend not to hang out together for much longer than it takes to do the necessary. Both males and females compete with one another by butting heads and clashing necks, although the males, having horns, tend to do more damage. Twins are unusually common for bovines, occurring in about half of all births, and even triplets have occasionally been reported. As with many animals, mothers go out of their way to hide their calves even from others of their own kind, keeping them concealed for the first month or so of their life. Today, there are not many wild animals about that will attack and eat nilgai, but wolves, leopards, lions, and tigers, are all potential threats, and likely were more so when they were more common in India than they are now.

Male four-horned antelope
The nilgai is the largest antelope in Asia. It is surprising then, that its closest living relative is, in fact, the smallest of all bovine species. This is the four-horned antelope (Tetracerus quadricornis), often known today by the local name of "chowsingha". Genetic studies indicate that the two species diverged no more than around 3 million years ago, during the late Pliocene, but the physical differences between them today are striking.

It doesn't take any great insight to work out what the most distinctive feature of the four-horned antelope is. In fact, it is the only species of wild mammal living today to have four horns, a feature it shares only with some domesticated sheep. With a slender build and a plain, tan-brown coat, four-horned antelopes stand just 55-66 cm (22 to 26 inches) tall at the shoulders. Only the males have horns, and some only have the two hind ones, or else the forward pair are so small as to be no more than fur-covered bumps. However, the horns that are present do have the same structure as those in nilgai, albeit being much shorter. Another point of similarity is that the four-horned antelope is the only other species of bovine to have scent glands in front of the eyes - in their case, however, they are much larger than those in nilgai.

Four-horned antelopes are found only in India and Nepal, and are slightly less widespread than nilgai. They prefer open woodland and hilly terrain, especially where there is enough vegetation to allow them to hide from predators - a more serious risk for them than for their larger cousins. They focus on particularly nutritious food, such as soft leaves, fruit, and flowers, and according to one study, have a particular preference for legumes.

They are, for the most part, solitary animals, preferring concealment over fleeing from predators, and are rarely seen in groups of more than two. This, together with their small size and natural timidity, makes them difficult to observe, and they have been far less studied than have nilgai. We know that they use the large scent glands on their faces to leave markings on bushes and similar features, and there is also some suggestion that, like nilgai, they tend to defecate in the same places repeatedly - although the resulting piles are smaller and far less obvious.

The antelopes breed throughout the year, although more commonly in mid-summer, and, despite their much smaller size, have roughly the same eight-month pregnancy that nilgai do. They give birth to twins more often than to singletons, although most studies suggest that it is rare for both young to survive their first year.

Despite being, physically, the least cow-like of all the bovines, the four-horned antelope (along with the nilgai) is known to be more closely related to domestic cattle than to the spiral-horned antelopes of Africa. Apart from the "four horns" thing, they may well resemble the very earliest bovines, the ancestral stock from which everything else evolved. And, next time, I will wrap up the bovines by looking at some of the fossil species that have come and gone since...

[Photos by Bernard Dupont, from Wikimedia Commons, and Kalyan Varma, released under the GNU Free Documentation License, Version 1.2.]

1 comment:

  1. Thank you for posting this!
    The Four-Horned Antelope has long been one of my personal favourites. The American Museum of Natural History has (in the Asian Mammals gallery) a group of stuffed specimens. Unlike their more flamboyant "habitat groups," this exhibit is not set into the wall, but in a glass box that can be viewed from three sides (fourth is against the wall), and you can examine the tops of heads from a distance of about two feet. And see the variety of head-gear: one male has four horns (the front pair much smaller than the rear), another is more like two horns and two bumps.