Genetic studies have suggested that S. celebensis might not be monophyletic, instead they form two clades, one restricted to north Sulawesi, and the other to the remainder of its range. This can be explained either by the occurrence of two colonization events onto Sulawesi, or the historic fragmentation of the island into at least two parts. Taxonomic differentiation between the two clades is not sufficiently supported by morphological studies, although the average skull size was found to be considerably greater for south Sulawesi than for north Sulawesi.

Sus celebensis is a species of the central and eastern islands of Indonesia, occurring east of the Wallace Line which separates the faunas and floras with Oriental affiliation in the west from the Australasian ones in the east. S. celebensis has a patchy distribution on most of Sulawesi Island, but it is most common in the south- eastern parts of the island. The species has been considered scarce in south Sulawesi for over two decades because of ongoing deforestation and hunting, and even in 1938 it was already remarked how few signs of pigs were seen in various parts of south Sulawesi. The species is thought to be extinct on Selayar Island, which lies off the coast of South Sulawesi Province. S. celebensis also occurs as a native form on the islands of Buton, Kabaena, Muna, Peleng, Lembeh and on some of the Togian Islands.

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Pigs have been widely spread through the Indonesian archipelago and beyond in domestic form. This primarily involved domestication of S. scrofa, but also S. celebensis, the only other species of pig that was successfully domesticated. Mitochondrial DNA studies of the dispersion of these domesticated forms have drawn different conclusions, but agree on three major dispersal events, two involving S. scrofa and one S. celebensis. Evidence supports an early human-mediated translocation of the S. celebensis to Flores and Timor and two later separate human-mediated dispersals of domestic pig (S. scrofa) through Island Southeast Asia into Oceania. In addition to Flores and Timor, S. celebensis is also thought to occur in its domesticated form on the islands of Halmahera, Lendu, Roti and Savur, and even on the islands of Simeulue and Nias, to the west of Sumatra and far away from its island of origin Sulawesi. In the Mollucas, and possibly elsewhere in this region, the introduced S. celebensis are thought to have hybridized with other introduced pigs of S. scrofa derivation, and apparent hybrids between these species are now reported to survive on a number of islands in this region, including Salawatti, Great Kei Island, Dobu, Seram, Ambon, Bacan, Ternate, Morotai and New Guinea. It is also reported that in the 19th century the sows of domestic pigs in Sulawesi frequently mated with wild animals after which they returned to their villages.

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S. celebensis is reported to occur in a wide variety of habitats, including rainforests, swamps, high grassland terrains, and agricultural areas. They are found at altitudes up to moss forest at about 2300 m, but they prefer valleys.

Head-body 800–1300 mm; shoulder height 70 cm; weight 40–70 kg. Adult animals are usually dark-haired, although some individuals are reddish-brown or yellowish in color, sometimes with lighter colored hairs on the trunk and abdomen. There is always a dark dorsal stripe, and a clear yellow snout band is usually present. A short mane and distinct 'crest' of longer hair on the crown or forehead has been recorded on captive animals, but observations on 27 animals in the wild in north Sulawesi found no instance of this crest as long as the in the zoo specimens. This might be because, like in S. cebifrons and S. philippensis, prominent manes and crests may only occur during breeding season (which in the case of these latter species runs from late November to April). It is unclear when the wild observations on S. celebensis were made.

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Young are born with five dark brown and six light horizontal stripes along the length of their bodies, which they lose after about 6 months of age. Adult males have three pairs of facial warts, the preorbital pair being the largest, the infraorbital somewhat smaller and the mandibular warts emerging from a whorl of hair marking their position to enlarge and eventually dominate (in captive specimens at least). The legs are relatively very short, and the back is short and slightly convex. The tail is long and simply tufted. Adult males are larger than sows, averaging 70 cm at the shoulder in males as opposed to 60 cm in females. Recent forms are larger than the sub-fossil remains found in caves in Southern Sulawesi.

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Similar to other species of Sus, S. celebensis has a chromosome number of 38. There are significant differences in the banding of the Y chromosome of S. celebensis, however, when compared with either S. scrofa or S. verrucosus.

Little is known about the feeding behavior of S. celebensis. Roots, fallen fruit, leaves and young shoots are thought to constitute the bulk of their diet, with invertebrates, small vertebrates and carrion as occasional secondary additions. However, no quantitative data are available about percentages of these items in their diets, and how this varies over time and between different habitat types. Unlike babirusas, S. celebensis has been observed to consume grasses, although this is based on brief observations only.

S. celebensis is primarily diurnal. Most feeding activity as observed in relatively undisturbed areas, occurs during the daylight hours, being concentrated in the early morning and late afternoon. Few data exist on group size, but observations around a salt-lick site recorded single animals (5 times), pairs (2 times), groups of three (4 times), and one group of six. In another population the sex ratio of adults was found to be 1:1.25 (n=25) and group size varied between 2 and 9, with an average of 5 individuals (n=16). Groups generally consisted of 1–3 young, 1–2 subadults and 1–3 adults. This and observations from the 19th century suggest that the species occur in small troops or families.

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Densities range from 0.4–2.0 animals/km² in a reserve on the north peninsula to 1.8–19.8 and 5.1–14.5 animals/km² in two reserves on the south-east peninsula, with a recent study in of those reserve finding even higher densities in lowland forest (23.5 animals/km²). Such major differences in densities are thought to result from varying hunting pressure related to religion, with Muslim-dominated areas, where people do not eat pigs, having higher densities than areas where Christians predominate. With inter-island trade being common, however, it is unclear to what extent Muslim-dominated areas become suppliers to the Christian ones. Also, in the south-east Peninsula which is mostly Muslim, S. celebensis has apparently been extirpated and obviously religious affinity is not a sufficiently protective factor to prevent local extinction of the species.

Mating is thought to occur February, although this is based on one observation only. Birth can occur at any time throughout the year but sows usually have their young in April or May. Gestation length is not known for certain, and the suggestion that it may lie between 16 and 20 weeks should be treated with caution. Farrowing sows give birth in nests made of grasses, leaves, branches and twigs, piled over a shallow excavation of approximately 2 m in length. Litter size has been estimated to range from 2–8, with an average of five, although a study North Sulawesi in 1991 found 6 pregnant sows killed by hunters to be carrying only 1–3 fetuses with a mean of only 2.17 fetuses per pregnancy.

Generally the species is considered to remain common, although statements along these lines have been repeated for decades without actual field surveys providing supporting information. The latest assessment of The IUCN Red List rated the species as ‘Near Threatened’ based on the level of the main threats, habitat loss and hunting. Wide scale deforestation for timber and conversion of land for agriculture, coupled with human population expansion and immigration have resulted in the marked contraction and fragmentation of its range in most places. Market surveys also indicate high take-off levels of S. celebensis. For example, brief surveys of three villages markets in northeast Sulawesi concluded that about 2 to 20 wild pigs per week were being brought by these commercial hunters and slaughtered by butchers when needed. Wild piglets that are also caught by villagers in Sulawesi are kept and are usually raised for slaughter for eating or sold at the local market. The high volume of trade in this species raises concerns about the sustainability of the current harvesting rate. The fact that the species is not protected outside the protected area network and can therefore be openly hunted and traded presently makes it difficult to reduce take-off to more sustainable levels. Surveys within protected area also show that the species is commonly hunted there, and in three protected areas in north Sulawesi no sign at all was found of S. celebensis. It is clear that there are few if any areas where the species can be considered secure.

S. celebensis is of particular interest in that it is the only pig species, apart from S. scrofa, which has been domesticated and quite widely transported by human agency outside its original range. The available evidence indicates that it is still maintained as a domesticate in some areas, but its commercial importance and future potential as a genetic resource are virtually unknown.

Text adapted from: Meijaard, E., J. P. d'Huart, and W. L. R. Oliver. 2011. Family Suidae (Pigs). Pages 248-291 in D. E. Wilson, and R. A. Mittermeier, editors. Handbook of the Mammals of the World. Vol 2. Hoofed Mammals. Lynx Edicions, Barcelona, Spain.

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