Bawean Hog Deer

MammalIndonesia

13 Jun

Axis kuhlii

The Bawean hog deer is the rarest deer in the world. It's only found on the small Indonesian island of Bawean and is considered 'critically endangered' — with an estimated population of fewer than 300 individuals.

Most people think of deer as shy, but fairly common forest animals. There are estimated to be over 35 million white-tailed deer in the United States, while in Europe, roe deer number over 15 million. Reindeer, or caribou, have a population of over 7 million.¹ In Japan alone, there are estimated to be over 3 million sika deer. And there are more than a million elk and moose — the largest living deer — across North America and Eurasia. But these are just the most prolific and well-known members from a family of 55 living species.

A tufted deer (*Elaphodus cephalophus*).

Among the lesser-known are lithe brockets with toothpick antlers that sprint through the forests of South America, living alongside their squat pudú cousins — the smallest of Cervidae — who almost look more dog than deer. There are muntjacs with flaring scent glands on their faces, whose barks echo across the forests of South and Southeast Asia, and tufted deer from East Asia, who bear sets of vampire fangs. While the white-tailed, roe, and sika deer populations thrive (to excess, in most places), many deer are in decline. Of the 56 evaluated deer species, 16 are listed as vulnerable, 6 are endangered, one is extinct in the wild, and one is just flat-out extinct. Two species, critically endangered, is nearly lost. One is a muntjac, a big-antlered barking deer that lives in the rugged Annamites on the border of Laos and Vietnam. The other is isolated on a single island.

Bawean

Bawean is a small Indonesian island in the Java Sea. It is roughly circular in shape, with a volcano rising from its centre, and tropical forests carpeting its many hills — exactly 99 hills, according to Bawean oral tradition. Across those hills, through a dense understory of ferns and mosses, quietly tiptoes the rarest deer in the world.

The Bawean hog deer doesn't look all that special, especially next to alien-esque muntjacs and vampiric water deer. In fact, it wouldn't look too out of place in the forests of Europe or North America among the white-tailed, the roes, and the reds. The Bawean deer stands atop stout legs, around 70 centimetres (2.3 ft) at the shoulder, its body covered in teak-brown fur, with white accents on its throat and chin, and light rings around its eyes. It has a relatively short muzzle and a relatively long (20 cm/7.9 in), fuzzy tail. You might not look twice if you saw one cross the road.

If you are lucky enough to spot the rarest deer species on Earth, it'll probably happen along the narrow stretch of flat beach in the southwestern part of the island. Otherwise, the Bawean hog deer inhabits the thick cover and steep slopes of the upland forest. It wakes at dusk from its dense bed of vegetation and treks through the forest with its head hung low, ducking branches and foliage, moving in a crouch with a hog-like gait. Most hog deer walk the night alone, tracing well-worn paths through the forest, but sometimes a buck is seen trailing a doe through the forest, or a doe is seen with her fawns. One is usually the cause of the other.

Barking Deer

The Bawean hog deer doesn't like to be seen, but it has no qualms with being heard. Both sexes of hog deer bark — like the muntjacs, or "barking deer" — and their vocalisations can be heard up to 100 metres away through the dense forest foliage, even by human ears. A bark is usually an invitation, beckoning nearby hog deer to approach and make contact, typically in one of the open clearings that pockmark the dense forest. Often, a bark is a challenge.

When two bucks, their branching antlers fully grown and sharp-tipped, enter a clearing, they begin their duel as any gentlemen would: with a shouting match. Each buck barks aggressively at his rival, snorting and stomping his hooves. If a receptive female is nearby, their barking bout may escalate into a locked-horn battle. After the duel, the victor mates with the doe and then skulks off into the forest. Seven and a half months later, the doe gives birth to a fawn, its coat faintly spotted with white. They, mother and fawn, also call to one another; if separated, the mother cries out to her fawn and the fawn squeaks back a high-pitched note that can only be heard over short distances.

Oddly, for such a chatty species, the Bawean deer doesn't have an alarm call. When alarmed, its protocol is to sneak quietly into the thick foliage and escape unnoticed — or sprint and then sneak, if startled — and if a hog deer is approached while it's hiding, it often just stays there in the hope it hasn't really been seen. Perhaps this solitary animal sees no benefit in alerting its neighbours of danger. To be fair, for most of its evolutionary history, there was little danger to worry a Bawean hog deer on its little island. A mother may well worry when she's separated from her fawn, for reticulated pythons live on the island, and a fawn would make for a body-bulging meal (one python was even found with an adult deer in its stomach), but these giant serpents are rare, and them aside, there are no predators on Bawean that would threaten the hog deer — or rather, there are no native predators.

Humans & Hog Deer

It's uncertain when humans first settled on Bawean, but our species seems to have been present for at least 500 years. Humans have historically had a love for hunting big game, and the original Baweans were likely no exception. The island hosts two large ungulates, or hoofed animals — the Bawean warty pig, a subspecies of the Javan warty pig, and the Bawean hog deer — and, given our track record with other large fauna across the globe, it's almost miraculous that both species are still around today. Hunting of the Bawean deer ended in 1977 — the deer is one of the 25 priority species legally protected by the Indonesian government — but danger from humans was replaced by danger from our best friends. Observations carried out over a two-year period found that feral dogs were responsible for 9 out of 11 Bawean hog deer deaths, the leading cause of mortality for the species.

Located some 150 kilometres (93 miles) north of Java — the world's most populated island, with 157 million people — modern Bawean hosts a modest population of around 70,000.² Modest in comparison to Java, yes, where the population density is an extremely tight ~1,100 people/km², but Bawean is a small island. It has an area of 197 km², around the size of Washington, D.C., and smaller than Inner London. Its population density is ~357 people per km² . Compared to Java, it's desolate, but the average density across all of Indonesia is only ~150–160 people/km² — in the United States, it's ~36 people/km². Under the weight of so much humanity, most of the virgin forests on Bawean have groaned and toppled. In 1975, only 27% of the island remained forested, and some 60% of that was mostly teak plantations, with only 40% representing natural forest. Between 2010 and 2020, the island saw a 36.6% decrease in its already sparse forest vegetation cover.

As forests fall across the island, Bawean hog deer are forced onto steep slopes that loggers can't easily clear.³ At night, they forage on wild almonds and bangkinan fruit when they're in season, or venture into agricultural fields to feed on corn, cassava, and the grasses that grow between the crops. It's estimated that, every day, a single deer produces 13 fecal pellet groups — that is, piles of poop. Knowing this, researchers have been able to make an estimate of population size; there are likely fewer than 300 Bawean deer left on the island. A later survey, one that used camera traps instead of poop pellets tallies, came up with an estimate of 120–277 mature individuals.

Fewer than 300 individuals represent the entire species.

Animals of Habit

Humans are animals of habit. No matter how spontaneous some of us might seem, we still like to have some kind of structure; some activity we do, place we go, or person we meet, that we can rely on to be a constant in our everyday. We're comforted by making that cup of coffee in the morning, eating a familiar meal, and walking a certain path through the park. That tendency didn't just arise suddenly in our species. Having habits — feeling the need to consistently accomplish certain tasks in a certain way, with those tasks getting easier and less mentally straining over time — helped our ancestors to survive, and so that trait was passed down to us. And, if what we observe in the natural world is any indication, habitual behaviour has come to us from a long, long line of ancestors that we share with many other animals. The Bawean hog deer, for one, has clear habits. Each night, it travels down a well-defined set of paths to reach the best foraging sites and, every sunrise, it returns to its patch of foliage to sleep, going back to the same bed several days in a row.

A disruption to our habits causes us some amount of distress. There's no reason to assume it's different for the hog deer. In reality, it's a lot worse. How many deer must have lost their homes to habitat destruction? Imagine coming home to not only find your bed destroyed, but your apartment too, and the whole neighbourhood completely levelled — gone are the streets you walk, the parks where you meet friends, and the supermarkets you rely on for food. You have to find a new place to live, a place that provides all your necessities, where you can re-establish your daily routines — but housing is being torn down all around you, your neighbours are being savaged by stray dogs, and you're on an inescapable speck of land surrounded by sea.

¹ A reindeer is a Eurasian caribou, and a caribou is a North American reindeer — they’re the same species, just called by different names. Their population of over 7 million is split between the two landmasses, with around 3.5 million in North America and 4 million in Eurasia. However, about 3 million of the Eurasian population belong to semi-domesticated herds.

² The actual population of Bawean is smaller, since a large portion of the Bawean population temporarily lives and works in other parts of Indonesia. The vast majority of those absentees are male, causing the island's actual population to skew female (77%), and, as a result, it's often referred to as "the Island of Women".

³ “Secondary forest appears to be ideal Bawean deer habitat, supporting densities of 19.2 deer/km². Primary forests, teak (Tectona grandis) forests with understory, and areas with teak and lalang support densities of 3.3–7.4 deer/km². Disturbed primary forest, and teak without understory - support only 0.9–2.2 deer/km².” (Ultimate Ungulate)

There are four species of (non-fascistic) Axis deer — that is, those in the genus Axis — including the chital, or spotted deer, found across the Indian Subcontinent, and three species known as hog deer (named for their hog-like way of trekking through forests). The most common and widespread, although still endangered, is the Indian hog deer, ranging from Pakistan to Thailand. The Calamian hog deer, a native of the Calamian Islands of Palawan province in the Philippines, is also endangered. And finally, there's the Bawean hog deer of Bawean, Indonesia; the rarest and most endangered (critically so) of the lot.

**Where Does It Live?**

⛰️ Forest with dense undergrowth.
📍 Bawean Island, Indonesia

‘Critically Endangered’ as of 17 Nov, 2014.

IUCN

Size // Medium
Length // 140 cm (55 in)
Weight // 50 - 60 kg (110 - 132 lb)
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: 15-20 years
Diet: Herbivore
Favourite Food: Grasses, leaves, and twigs 🌿
Class: Mammalia
Order: Artiodactyla
Family: Cervidae
Genus: Axis
Species: A. kuhlii

Bawean hog deer are nocturnal and known to walk along well-trodden paths through thick foliage — moving in a crouch with a hog-like gait (hence the name). They often return to the same bed of vegetation for several days in a row.
Both sexes bark, and their vocalisations can be heard up to 100 metres away through the dense forest. When separated, a mother calls to her fawn with a cry, and the fawn responds with a high-pitched squeak that only carries over short distances.
Hunting this deer has been illegal since 1977 — it is one of 25 priority species legally protected by the Indonesian government — but the species is still threatened by dogs. Observations over a two-year period found that feral dogs were responsible for 9 out of 11 Bawean hog deer deaths, making them the leading cause of mortality.
Of the 55 deer species, only two are critically endangered: the giant muntjac of the Annamite Mountains and the Bawean hog deer. As of its last evaluation in 2014, the Bawean deer population is considered stable.