Sunday 20 May 2018

The Pig Family: The World's Largest and Smallest Pigs

Pygmy hog
By some definitions, the term "pig" can really only be applied to those species that are most closely related to the domestic animal; those included within the genus Sus. This includes the wild boar, and the various kinds of warty and bearded pig that inhabit the Indonesian and Philippine islands.

But these are not the only pig-like animals to inhabit Asia. In 1847, Brian Hodgson, a naturalist and former colonial administrator who was living in Darjeeling at the time, described and named the pygmy hog (Porcula salvania), an animal he considered so different from regular pigs in the shape of its teeth and feet that he placed it in its own, newly defined, genus, Porcula. (The scientific name, incidentally, translates as "piglet from the Sal Van", the latter being a forest that only coincidentally sounds like the Latin "silvae" meaning "woodland").

However, it turned out that the individual he was looking at wasn't an adult, as he had been told by those who had collected it, and that some of the features he was relying on to distinguish it from true pigs weren't fully developed yet. When, in 1863, the great naturalist John Edward Gray accidentally gave it a new name (apparently not realising it already had one), he placed it in Sus, under the rather magnificent moniker of S. lilliputensis. A more thorough review in 1883, looking at a wider range of specimens and considering the full details of their internal anatomy, concluded that Gray had at least been right about the animal being a true pig, and that any differences that might exist were too minor to be significant, and firmly placed it as Sus salvanius.

It took over a hundred years before anyone began to say "no, really, this does actually look kind of strange" and wonder if Hodgson had been right all along - if probably for the wrong reasons. In 2007, genetic testing provided the proof, and the original scientific name was officially restored. Porcula it is.

The most obvious difference between the pygmy hog and its relatives is that it is much smaller than any other species of pig (or suid, if you prefer). Fully grown adults stand around 26 cm (10 inches) tall at the shoulder, and weigh no more than 12 kg (26 lbs), and usually quite a bit less, especially in the sows. This is, for a pig, positively tiny. Moreover, proportionately speaking, pygmy hogs also have unusually small ears and short tails, and the sows have only six teats, rather less than those in wild boar and their relatives. There are also some minor differences in the shape of the feet and of the snout.

Part of the reason that such differences escaped the attention of zoologists for so long is that the pygmy hog is rare and lives in a relatively inaccessible location - for much of the late 19th and early 20th centuries, nobody had a decent specimen to look at. Hodgson's original had been found in Sikkim, but, at the time, they seems to have lived all along the southern boundary of the Himalayan foothills, from Nepal and Uttar Pradesh to Bhutan and Assam. It's possible that it was once found further south, as well, but was forced to retreat to the wild hills by the expansion of agriculture in the heavily cultivated lowlands.

Today it mostly lives in grasslands where the grass is high enough to conceal them, but that are dry enough not to be prime agricultural land - and most likely not prime feeding ground for the pigs, either. The little we know of their behaviour comes from studies of captive animals, which suggest that they prefer to be active during the day, and spend most of their time searching for food. They also groom one another, with males preferring to groom females where possible, presumably to establish a social bond. Like most other pigs, they are highly omnivorous.

An unusual habit is that pygmy hogs regularly construct nests from the grass in which to rest during the heat of the day. In other wild pigs, nest-building is common enough, but is only performed by sows, and then only while farrowing and raising piglets. But among pygmy hogs, both sexes do it, and do so year-round. In fact, breeding is far more seasonal than in wild boar, with the piglets being born just before the start of the monsoon. The female members of the litter, which typically only consists of three or four piglets, remain with the mother even after reaching maturity, while males seem to be more solitary.

While pygmy hogs were not traditionally hunted in significant numbers, they have suffered hugely from the loss of their natural habitat to agriculture, in particular the slash-and-burn type. Already rare when they were discovered by Europeans in the 19th century, they are now virtually extinct, with only two or three hundred left alive, all in the depths of the Manas National Park, around the upper reaches of the Brahmaputra River in northern Assam. This is small enough that even a relatively minor amount of illegal hunting would be enough to cause a risk, and the fact that it was recently shown that pygmy hogs can catch swine fever from domestic animals is also a potential risk.

A number of pygmy hogs do exist in captivity, as part of a project to maintain the species, and attempts to reintroduce them to the wild have been successful, at least in the short term. Nonetheless, they remain the single most endangered species of pig, teetering on the cusp of extinction.

Giant forest hog
At the opposite end of the size scale is the forest hog (Hylochoerus meinertzhageni). There are three confirmed subspecies, found across the central regions of Africa from Guinea to Kenya, and a possible fourth one in Ethiopia. Most of these are, if anything, slightly smaller than the wild boar, but the subspecies found in and around Kenya is just slightly larger, and thus, the world's largest wild pig. This subspecies, which goes by the lengthy scientific designation of Hylochoerus meinertzhageni meinertzhageni, is commonly known as the "giant forest hog" and the latter name is sometimes, perhaps misleadingly, applied to the species as a whole.

The forest hog is an almost black, shaggy animal with a heavy build. Full-grown boars can reach 110 cm (3'7") at the shoulder, and weigh up to 275 kg (600 lbs), although, as noted above, this does depend on the subspecies. Other distinguishing features of these hogs include the large, hairless, cheeks, and an unusually large nasal disc. Males have prominent bony ridges on the forehead that are so large that the true, un-ornamented, forehead is reduced to a deep depression in the centre, and large and thick tusks that flare out sideways from the mouth.

As their common name suggests, these hogs are found in forested areas, but they aren't so common deep inside the jungle. Instead, they prefer the rainforest margins, utilising clearings and riverbanks where necessary, or the higher slopes of hills where the trees may thin out a little. This is probably to acquire a more mixed diet, although it's interesting that forest hogs are, unlike most pigs, herbivores, not omnivores. Like more herbivores, this doesn't mean that they literally eat no animal matter at all, but it's mostly just the odd insect or centipede that gets in the way, and the hogs' teeth and jaws seem adapted for a strongly leaf-based diet. The exact details vary throughout the year, as the rains come and go, and, while they are never true grazers, can include a high proportion of grass.

Forest hogs live in groups that average about a dozen individuals, spread out over three generations. The males vigorously defend the group from potential predators - and humans. They are generally more tolerant of their own kind, however, and different groups can share parts of the same territory, or even band together temporarily. When they aren't foraging for food, they spend hours at a time just wallowing in the mud to cool off, and, like many animals in that part of the world, while they aren't nocturnal, they do take an additional snooze in the middle of the day when it becomes too hot.

During the breeding season, things do get more intense for the boars, who can clash with one another in contests that are as much about stamina as sheer strength - fights can last up to half an hour before they get tired, and can become so violent that one of the competitors later dies of a fractured skull. Litters are typically born around the start of the rainy season, and consist of up to six piglets. Since sows only have four teats, this means that sometimes they produce more young than they can comfortably feed; in most other animals this would lead to certain death for the young that luck out, but, in their case, sows don't seem to mind whose piglets they are suckling, so those with smaller litters can help out those with larger ones.

The forest hog population is thought to be decreasing, but it's sufficiently large and widely distributed, and the rate of decline sufficiently small, that they are not under any particular threat as a species. Locally, of course, things may be different, and they have vanished, for example, from Equatorial Guinea. A couple of points do stand in their favour. For one, while they can catch the local form of swine fever from domestic pigs, they are immune to its effects, and rarely spread it back again. Even better for them, they apparently taste terrible, and so are rarely killed for bushmeat. (Apparently, when they are, the poachers smoke the meat and pretend it's something else, but there's probably only so many times you can do this before your customers notice).

There's a similar story among the other pig species of Africa, none of which are endangered, as so many of their Asian kin are. The best known African pigs are probably the warthogs, but before we look at them, I'm going to turn to two of the lesser known species...

[Photos by A. J. T. Johnsingh and Michell Zappa, from Wikimedia Commons.]

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