Sunday, 17 June 2018

The Pig Family: Bush Pig, Bushpig, Red River Hog

Red river hog (boar)
As zoological knowledge has advanced, the number of species that we know about has changed regularly, and not just because we keep discovering new ones. Animals that we knew about, but previously thought were subspecies get promoted to full species, and animals that we thought were separate species turn out not to be.

In fact, over time, we can sense something of a trend here. Beginning with Linnaeus in 1758, several new species are named, often by naturalists unaware, in the days before fully up-to-date reference libraries, let alone the internet, that somebody else had already given a name to the same thing. That process continues through the 19th century, with minor differences being seized on as evidence of speciation, even where it was possible to make decent comparisons. Through the 20th century, the number of genuinely new species being discovered dramatically tails off (at least, for mammals), but there's also a tendency to tidy up the great mass of inherited names from the past, merging similar animals together. Finally, from the late 20th century onwards, an increasing understanding of genetics results in numerous subspecies being promoted, often with our Victorian predecessors turning out to have been right all along.

Linnaeus identified four species of wild pig, two in Africa, and two in Asia. By the end of the 19th century, several more had been described, under a variety of different names. In 1904, the giant forest hog of equatorial Africa was added to the list as a genuinely new discovery, but there were at least eight others already named on that continent alone. And then followed the process of whittling those down. In the 1920s, we were down to five African species, four by the 1940s, and, finally, by the 1970s, we thought that there were just three: the warthog, the forest hog, and one other, called the bushpig.

And then, in 1993, came the reversal, when it became clear that there were, in fact, two different species of bushpig. This, of course, immediately raised the question of which one it was that Linnaeus had described, and which one was therefore 'new'. Linnaeus, it turned out, had simply said that he was talking about the one 'in Africa', which didn't really help matters, but further investigation revealed that he had probably meant the western half of the continent. Since Frédéric Cuvier had named an eastern species in 1822, we now had pre-existing scientific names for both kinds of bushpig.

One remaining problem was that both animals were simply called "bushpigs" in English, and, even today, many sources use that common name for both of them. Some bright spark suggested that we call one the "bush pig" and the other the "bushpig", but this was clearly silly, and while I have seen this recommendation followed in even relatively modern scientific literature, today we normally call Linnaeus's original, west African, species, the red river hog (Potamochoerus porcus).

In fact, the red river hog is a highly distinctive animal, with an unusually thick pelt of hair for a pig, coloured in bright russet with a narrow white mane down the back, and black and white markings on the face. The ears have narrow tips that each end in a remarkably long tuft of hair, and males have prominent conical lumps on either side of their snout, but relatively small tusks. The red colour develops as the pig ages, with younger animals having a more brownish hue, and piglets having numerous yellow spots on a chocolate-coloured background.

Red river hogs inhabit the hottest, wettest, parts of tropical west Africa, along the Atlantic coast from Senegal to Gabon, and throughout the Congo River basin to the east. They inhabit dense rain forests, and, as their name suggests, are particularly common along river banks and in swampland. There is some evidence that they may prefer forests that have been subject to human logging but then allowed to regrow naturally - possibly because these areas have fewer predators. Otherwise, with the adaptability typical of pigs, they seem to be numerous just about everywhere, except where they are likely to run into forest hogs, which are much larger than they are, and probably after the same sort of food.

They are gregarious animals, with sounders including up to twenty individuals, and are most active at night or around dusk, resting in cool hollows during the heat of the day. Breeding appears to be seasonal, with sows coming into heat during the first part of the year, so that births are most common during the dry season. As might be expected, they are good swimmers, and can travel some distance along rivers in search of high quality food sources.

In places, they are common enough that they constitute about 20% of the diet of the local leopards, although a lack of leopards simply switches their main predator to human bushmeat hunters. In fact, they are particularly prized by hunters, and, while they remain common overall, they are becoming rare in some localised areas. For example, they have virtually vanished from Senegal, and are absent altogether from Gambia, which one might have thought would have been a good habitat for them.

Bushpig (sow)
Cuvier first identified the second species from a population in northern Madagascar, and it's this that we now call the bushpig (Potamochoerus larvatus). It's now thought likely that these Madagascan pigs belong to the same species as much more widespread populations on the continent proper, but they appear quite variable, and at least three subspecies are currently recognised.

Ironically, the ones on Madagascar don't count, since, while pigs in general, and bushpigs in particular, are good swimmers, the 250-mile Mozambique Channel is surely too much of a challenge. As a result, we suspect that they must have been brought to the island by humans (probably from what is now Tanzania), although quite when, or exactly why, is a bit of a mystery. Possibly, somebody attempted to domesticate them, but then gave up, although, if so, there's no evidence anyone ever did so on the mainland.

Bushpigs do look similar to their more westerly relatives. They are, however, slightly larger, on average, with sparser, but longer, hair and without the dramatic ear-tufts. Their colour is quite variable, and the fact that some are decidedly reddish doubtless helped reinforce the confusion with the red river hog that persisted in the '70s and '80s. Most, however, are a much more bland colour, without the strong markings of the western species, although they can be anything from cream to near-black.

They are found through much of East Africa, from Ethiopia to Cape Town, and even further west in Angola, south of the red river hog's distribution range. Although the climate in this part of the world is drier and more seasonal than that of the equatorial jungles, bushpigs, like river hogs, prefer to live in dense, lowland, forest when they can. They are, however, also found in more open woodland, and, in those stretches of central Africa where the two species live alongside one another, it is the bushpigs that are pushed up into the forested hills, while the river hogs keep to the lusher valleys.

Like other pigs, they are omnivorus, eating fruit when it is in season, and concentrating more on roots and tubers when it isn't. They are thought to be effective at dispersing seeds that pass through their digestive tracts, which red river hogs seemingly are not, because they chew up their food too efficiently. In fact, they have even been seen following monkeys about to eat the fruit that they discard.

They are, like red river hogs, mostly nocturnal, but this seems primarily motivated by a desire to avoid heat rather than sunlight per se, and they can be active during the day in the cooler parts of the year in South Africa. Their social structure also seems to be somewhat unusual for pigs, being relatively sophisticated, with some sounders having dominance over others, and involving boars helping to look after their piglets. Scent marking on trees and the like helps to keep sounders apart where resources are limited, with the boars resorting to aggressive, if ritualised, combat when that fails.

Leopards are, as with river hogs, likely their main predators, although they also have to worry about lions and hyenas. In some places, humans can be added to that list, but much of East Africa is Muslim, leaving pork off the menu. Even where this isn't so, in South Africa, deliberate eradication programs to reduce their population in order to protect crops have failed because the pigs are just too good at both hiding and breeding.

While red river hogs are relatively common in zoos, and so not entirely obscure, it's probably fair to say that the best known pigs in Africa, and likely the best known overall after the wild boar and domestic animal, are not they, but the warthogs. So it is to those that I will turn next.

[Photos by Bernard Dupont and Tim Vickers, from Wikimedia Commons. Cladogram adapted from Frantz et al. 2013, Gui-sheng et al. 2005, and Frantz et al. 2015.]

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