Pygmy Hog

MammalIndia

29 Jul

Porcula salvania

The pygmy hog is the smallest pig species in the world — standing just 25 centimetres (9.8 in) at the shoulder. It is also one of the rarest. Once widespread across the southern foothills of the Himalayas, fewer than 250 mature individuals now survive, confined to a small patch of grassland in Assam, India.

An adult wild boar — the ancestor of our domestic pigs — can measure nearly a metre (3 feet) at the shoulder and weigh upwards of 100 kilograms (220 lb). It ranges over much of Europe and Asia, as well as parts of northern Africa, and has invaded Australia and the Americas. It is adaptable and bold, unbothered by human activity and able to survive in forests, fields, or on suburban streets. Groups of boars, called ‘sounders’, create a grunting and crunching ruckus as they move through their territory. This pig is booming, brazen, and big.

The pygmy hog is the antithesis of the wild boar.

The Real Mini Pig

Of the 17 species of wild pigs, also known as suids, the pygmy hog is far and away the smallest. It is about the size of a stout house cat — standing just 25 centimetres (9.8 in) at the shoulder — but, weighing between 6.5 kg (14 lb) and 10 kg (22 lb), the hog is quite a bit chunkier. Still, that's 10 times lighter than an adult wild boar. Put them side by side, and the pygmy hog could be the boar's piglet. Admittedly, though, while the size would be about right, it would be a weird-looking piglet.

Unlike the fuzzy brown fur with splotches and stripes of a wild piglet, an adult pygmy hog wears a plain greyish-brown coat made up of bristly and rather sparse hairs. The hog also lacks a big, cute babyish cranium. In fact, it lacks any clear delineation between its head, neck, and body. Beginning at its porcine nose, its long snout widens into its head, which widens into its neck, which widens into its body, terminating in a dumpy rear end. You could call it streamlined, but it just looks rather back-heavy — a bit like an eggplant with legs.

Forests of Grass

In the sub-tropical grasslands of Assam in India, the grasses grow up to 8 metres (26 ft) tall, as if stretching up towards the high Himalayan peaks in the north. Within these towering forests of grass, beneath the tallest mountains in the world, live pygmy hogs. They travel in natal family groups of four to six — usually one or more adult females with their piglets — and spend up to eight hours a day foraging for roots and tubers, rooting through the soil with flexible snouts, and snacking on worms or any other grubs they can churn up. Every night, they retire to their beds: dug-out depressions in the ground, piled high with dry grasses.

At the beginning of a new year, in January or February, the usually solitary males — who look quite dapper with their whorled, pale "moustaches" — join up with a group. As the monsoons sweep over western Assam in late April and May, every hog family squeals with two to six newborn piglets. Hidden in thatch nests built by their mothers, each piglet weighs just 150 to 200 grams (5 – 7 oz). They venture out after about a week. After a month, they develop reddish stripes across their bodies, which help them hide among the grasses, and eventually fade as they mature into full-grown (if not large) adults.

The pygmy hog is rarely seen by humans. Even grasses just a couple of metres high would well hide a pygmy hog, and the hogs do well to stay hidden. The adults fear pythons and raptors, among other large predators, while the young are especially vulnerable, given that a newborn weighs less than a hefty rat and must contend with gnashing mongoose teeth, slashing cat claws, and stabbing crow beaks. Male pygmy hogs brandish sharp tusks, but these are so small they're barely noticeable. Their only recourse, really, is to flee and hide. Cut away the grasses, and these tiny hogs are defenceless against a deluge of predators hankering for pork.

Shrinking

During the Pliocene and early Pleistocene (5.3 – 0.8 million years ago), tall grasslands blanketed a much larger portion of South Asia than they do today. It's possible that, long ago, pygmy hogs ranged far across the Himalayan foothills and down into India, before grasslands began to contract in the Pleistocene; the Last Glacial Maximum restricted the hogs to a sheltered swath of tall grasses some 20,000 years ago.

Before the turn of the 20th century, those grasslands extended along the southern base of the Himalayas, and pygmy hogs trotted beneath the lofty mountains from north-western Uttar Pradesh and southern Nepal in the west to Assam in the east. Today, the pygmy hogs have been corralled into a small patch of tall grassland beneath the Himalayas in Assam. This time, it wasn’t a glacial period that shrank their range — it was us. The decline came not from ice but from fire, farming, and the steady degradation that followed the arrival of humans en masse.

Natural grasslands across the southern Himalayas were replaced by settlements and cultivated fields. They were altered to reduce flooding and 'managed' through tree planting and large-scale dry-season burnings. Tall grasses were rapidly replaced by short grasses. Natural grasslands were made more amenable to human use. As viable pygmy hog habitats were fragmented by towns and farms, increased contact with livestock meant a higher risk of disease transmission.

Efforts to conserve endangered animals — large and charismatic ones like rhinos, elephants, and buffalo — took priority over the plight of an obscure little pig species. Everyone wants to see a wild rhino or elephant. No one travels to see a pygmy hog. So the destruction of its grassland habitat continued, forcing it into smaller and smaller patches until only a few scattered holdouts remained in Assam.

The pygmy hog may have been more widespread in its heyday, but it was never very numerous. A genomic study of six pygmy hogs found that over the past ~1 million years, the species maintained a very small population size with low genetic diversity, and the frequency of homozygosity suggests that "the pygmy hog population has gone through past but not recent inbreeding" — at some point, the pygmy hogs had suffered a population bottleneck but recovered, at least partially, as evidenced by the lack of recent inbreeding.¹ Current estimates put the population of mature pygmy hogs at 100 to 250 individuals. In other words, we may be thrusting the species through another population bottleneck, one that it may not see the other side of.

Scarcity has left its mark on the pygmy hog gene pool: with such shallow genetic diversity, the species is poorly equipped to survive new diseases or adapt to changing conditions.

Specialist Hogs vs. Generalist Boars

The history of the pygmy hog's distribution conforms to a clear pattern: when the grasslands shrink, so does the hog's range. This is because the pygmy hog is a true ecological specialist, and being a specialist is a double-edged sword. If a specialist finds itself in the exact conditions for which it is adapted, it will survive with little issue, and likely even thrive. But, because specialists are adapted to a narrow strip on a vast gradient of possible circumstances, they're threatened from all sides. Threatened by what? Essentially, any kind of change. Any shift away from the conditions they're used to — whether that means a change in climate and habitat, the availability of a food source, or the arrival of a new player, whether predator or competitor.

The pygmy hog is a specialist of tall, sub-tropical grasslands. Tall grasses for hiding from danger, for taking shelter from the heat, and making thatched nurseries for their young — these are the narrow conditions to which the species is adapted. But given a long enough time span, change is inevitable.² That change could be caused by glacial-interglacial cycles; cold and dry glacial periods favour the expansion of tundra habitat at the expense of grasslands, while warmer and wetter interglacial periods allow forests to expand and encroach on grasslands. Or change could come, often quite swiftly, at the hands of humans, who cut and burn to reduce grasslands to short pastures or plant trees to promote forest growth. Regardless of the source — natural or human — or the direction — towards sparse fields or rich forest — any change imperils the pygmy hog.

Compare the specialist pygmy hog to its cousin and neighbour, the wild boar. While the pygmy hog depends on tall grasslands to survive, the wild boar is a habitat generalist. It roots through soil in forests, grasslands, and wetlands, steals crops from farmlands, and rummages through our trash in the suburbs. It lives at altitudes ranging from sea level to as high as 4,000 metres (13,100 ft) in the mountains of Central Asia and Kazakhstan. It survives the hot and humid rainforests of Southeast Asia and the -40°C (-40°F) winters of Siberia. It is found on every continent save Antarctica and, with our help, has invaded the most isolated islands, from Hawaii to Fiji, New Zealand, Guam, Mauritius, and the Galápagos.

Generalists often thrive at the expense of specialists, arriving during a change in conditions and outcompeting them. As tall grasslands were cleared and the pygmy hogs lost ground, wild boars moved in. Pygmy hogs simply couldn't compete with wild boars outside of the habitats to which they're adapted. The specialist species is stuck in its Goldilocks zone, and so the pygmy hog is only as stable as its grassland habitat. Over the past million years and especially the past century, its specialisation has meant an ever-shrinking world, and once that specific world is gone, so too is the pygmy hog.

While the wild boar thrives in the new world we’ve made, the pygmy hog is trying to survive in the few pieces we haven’t destroyed. Are pygmy hogs doomed to extinction, then, to be replaced by pervasive wild boars? They may not be elephants or rhinos, but to some, pygmy hogs are still worth saving. Starting with six founder hogs flushed from their native grasslands in 1996 (using the aid of elephants), a captive breeding programme has since bred and released over a hundred individuals back into the wild.³ If we can leave enough room for these smallest of suids, the pygmy hogs will vanish — not from existence, but into their tall forests of grass.

¹ Homozygosity is when an animal has inherited an identical form of a particular gene from each of its parents. This occurs more often in small populations, as they tend to have lower genetic diversity and frequent breeding between relatives with similar genes — meaning offspring are more likely to inherit identical copies of genes, increasing overall homozygosity in the population.

² Other species have also been affected by the destruction of these grasslands, such as the endangered hispid hare and the critically endangered Bengal florican.

³ Learn more about the Assam-based Pygmy Hog Conservation Programme (PHCP)!

**Where Does It Live?**

⛰️ Tall grasslands.
📍 Assam, India; southern foothills of the Himalayas.

Size // Small
Length // 55 - 71 cm (22 - 28 in)
Weight // 6.5 kg - 10 kg (14 - 22 lb)
Activity: Diurnal ☀️
Lifestyle: Social 👥
Lifespan: Up to 14 years in captivity
Diet: Herbivore
Favourite Food: Tubers 🍠
Class: Mammalia
Order: Artiodactyla
Family: Suidae
Genus: Porcula
Species: P. salvania

The pygmy hog is about the size of a chunky house cat, weighing between 6.5 kg (14 lb) and 10 kg (22 lb) — quite chunky indeed. Still, that's 10 times lighter than an adult wild boar. It’s also shaped like an eggplant with legs, with little evident delineation between its head, neck, and body.
The pygmy hog is a resident of the grasslands in Assam, India, where the grasses can grow up to 8 metres (26 ft) tall.
It lives in family groups of four to six — usually one or more adult females with their piglets (or hoglets) — and together they forage for roots and tubers, retiring every night to a “bed”: a dug-out depression in the ground, piled high with dry grasses.
As a new year rolls around, males will join a group and mate with the females. The resulting hoglets are born weighing just 150 to 200 grams (5 – 7 oz), developing reddish stripes across their bodies after about a week, helping them hide among the grasses. These eventually fade as they mature.
Male pygmy hogs brandish sharp tusks that are so small, they're barely noticeable. The smaller hoglets are even more vulnerable to predators like mongooses, cats, and crows. The defensive strategy of a pygmy hog, then, is to run and hide in the tall grasses.
This species is a grassland specialist: convert the grasses to low-cut fields or lush forest, and the pygmy hogs cannot survive. Many of the hogs likely vanished when the grasslands along the southern base of the Himalayas began to be altered at the start of the 20th century.
Today, the pygmy hog is an endangered species, with an estimated population of 100 to 250 individuals.