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VU - Sunda Bearded Pig

Sunda Bearded Pig (Sus barbatus)
Status: Vulnerable A2cd ver 3.1
Pop. trend: decreasing

Photo
Subspecies and Distribution
. Sus b. barbatus Müller, 1838 Borneo, Karimata, Laut, and Sibutu, and possibly extending to Tawi Tawi.

Sus b. oi
Miller, 1902 Sumatra and Peninsular Malaysia. Previously on Batam, Bintan and Rupat Islands, but present status is unclear.

Distribution (see map). The Bearded Pig occurs in Peninsular Malaysia, Sumatra, and on Borneo, including the Indonesian part (Kalimantan), the two Malaysian states of Sabah and Sarawak, and in Brunei Darussalam. It is also reported from the island of Sibutu, west of the Sulu Archipelago in the Philippines, and possibly on Tawi Tawi Island. In Peninsular Malaysia and Sumatra its distribution is now limited to a relatively small part of their presumed pre-historic range, while in Borneo the species is still widespread but declining. There are additional records from a range of smaller islands, where the status of the species is unclear but populations have possibly been extirpated.

Descriptive notes. Head–body 122–148 cm for females and 137–152 cm for males (although some reports suggests that males can attain a total length of 208 cm); tail 17–26 cm; hind foot 27–32 cm; should height 90 cm; bodyweights usually range from 58 to 83 kg, with females somewhat lighter than males. When food is abundant, weights of up to 200 kg can be attained.

Adult Bearded Pigs are characterized by their relatively large body size, a reduced degree of sexual dimorphism compared to other species of Sus, long legs, a "bearded" jaw or gonial tuft and sparse body hair. The species has smaller warts and a more elongated skull compared to the other warty pigs, relatively small ears, and a long tail with large terminal tuft divided into distinct anterior and posterior parts. The head is typically long with a ‘beard’ of bristles extending along the lower mandibles, extending up and across the snout as a thick band  above each side of the mouth with upward and forward pointing bristles. The race barbatus has long, sweeping cheek whiskers and thicker and longer hairs on the snout band (especially in males), as opposed to the whiskers of oi which are shorter on cheeks, but long, wiry over the snout. There has been suggestion that the body of oi is more bilaterally flattened than in barbatus, but this has not been confirmed.

The overall body coloration of Bearded Pigs varies from blackish in young pigs, to a paler reddish brown, yellow-grey or almost buffy white in adults. The color of mud wallows also affects the apparent color of pigs. Piglets of S. barbatus are longitudinally striped, black-brown and whitish to fawn and these stripes are lost by 6 months of age. Females have 6 pairs of mammae.

Habitat. Bearded Pigs are well-adapted to the extensive dipterocarp forest of Borneo, Peninsular Malaysia and Sumatra. This tree family if often dominant in lowland and hill forests, and is characterized by synchronized flowering and mast-fruiting. Bearded Pigs also make extensive use of riverbanks, where they root among herbs and look for earthworms. Other habitats used by Bearded Pigs include estuarine swamps, secondary and all kinds of old jungle, beaches, riverbanks, all kinds of plantations, clearings and also the outskirts of towns.

The species is well known for its migratory behavior related to the timing of food availability. They are scattered across large regions during non-mast fruiting times, but move from both mountain and swamp habitats to drier, lowland forest types when fruit becomes abundant.

Food and Feeding. Bearded Pigs are real omnivores and it has been said that "it is almost easier to state what they will not eat". They feed on a long list of food plants, but also consume roots, fungi, invertebrates in soil and rotting wood, small vertebrates, turtle eggs, and carrion. Fruit supply is believed to have particular influence in determining growth rate, fat deposition and reproduction, with the other foods as they normally occur in the forest assumed to allow only slow growth at best. The oil-rich seeds of members of the tree families Fagaceae and Dipterocarpaceae are thought to be especially important. During mast fruiting the majority of seeds in the diet is dipterocarps, although they can and will eat other species available. Oaks, especially Castinopsis spp. Lithocarpus spp. and Quercus spp. are also favorites. During fruiting times, they are almost solely seed predators, and Bearded Pigs play an important role in the distribution of seeds. They also consume a few figs (e.g., Ficus dubia), melastomes and other tiny, hard testas, which can pass through their guts and germinate. 

Activity patterns. Bearded Pigs are mostly diurnal. They are subjected to irregular migrations, seeming to follow the fruit when in season so that one year a particular spot may swarm with them but not be troubled again for many years after. Especially the ripening of illipe nuts (Shorea sp.) in Sarawak and East Kalimantan, appears to be significantly correlated with pig migrations. These lemming-like mass migrations of Bearded Pig are quite distinct from the annual local movement damaging rice fields, and do not appear to be food related. The somewhat forced, lemming-like aspects of these large scale pig migrations have been pointed out, and exemplified by the observation of a pig whose hind quarters were paralyzed and which pulled itself forward by its front legs to follow its conspecifics. The appearance of large numbers of pigs traveling together is especially obvious during river crossing, which they do in groups of over 100 animals. This provides local hunters with the opportunity to kill large numbers of pigs for meat and fat, from which they extract oils. Mass river crossing might have evolved at a time when crocodiles were still abundant in the region.

Bearded Pigs appear to exist in different population states, which have been summarized as follows:

a)      Dispersed, static populations exploiting small, dispersed, unpredictable and discontinuous ‘background’ food sources. Low breeding and growth rates possible. Local movements only. Example: typical mixed dipterocarp forest in Borneo between generalized fruiting episodes.

b)      Small to medium populations exploiting concentrated, predictable and continuous ‘target’ food sources. High breeding and growth rates possible. Local movement only. Example: Koompassia – Burseraceae forest in Peninsular Malaysia.

c)      Small to medium populations, with members aggregating to exploit large, dispersed, unpredictable food sources. Breeding and birth rates depend on success of matching movements to fruiting within a dynamic phenological mosaic. Short to medium-range movements. Example: typical mixed dipterocarp forest in Borneo between generalized fruiting episodes.

d)     Small to large populations moving regularly to exploit concentrated, predictable and discontinuous target food sources. Breeding and growth linked to activity of food sources. Short-range to long-range movements. Size of population varies from year to year depending on background food supply. Examples: Dryobalanops aromatica association in Peninsular Malaysia; Dinochloa association in Sabah.

e)      Large and expanding population exploiting an exceptional supply of background food available over a period sufficient for several litters to be raised to sexual maturity. High breeding and growth rates characteristic. Long range movements. Example: interior of Sarawak in 1954, 1959, 1983 and 1987.

f)       Very large and collapsing population having exceeded background food supply. Low breeding and high death rates. Increasingly desperate long-range movements. Example: starving herds reported from Malaya and Borneo.

It remains largely unstudied how these different population states have been affected by the continuing loss, degradation, and fragmentation of forest habitats. Unconfirmed information from local people in Kalimantan and Sarawak suggests that mass migrations of pigs no longer occur to the same extent as reported formerly, even as recently as the 1980s and early 1990s, which might indicate that with the removal of millions of hectares of high timber value dipterocarps food dynamics and related population states have been severely disrupted.

Movements, Home range and Social organization. The basic social unit is that of the mother family, a female and her litter. These units often join up, and much larger aggregations are formed occasionally, with scores or even hundreds of pigs traveling together. Fully adult males seldom associate with the natal groups. The ranging varies so much throughout the year and between years that no home range estimates can be reliably made, unless animals are radio-tracked for several years. Such studies have recently been completed in Sabah, Malaysia, but data are not yet forthcoming.

Bearded Pigs are powerful swimmers that easily cross the many large rivers of Borneo and Sumatra. They have also been reported to cross sea barriers, which might explain why they occur on so many small islands. A report from the 19th century mentions droves of pigs swimming across the Klumpang Bay in west Borneo, a distance of about 8 km. There are numerous, apparently reliable, accounts of wild pigs crossing the sea channel between Sabah and Sibutu (a distance of at least some 45 km), and also across the Kowie harbor near Tawau, which is at least 9 km across. Another Bearded Pig was found swimming in de middle of the Sandakan Bay in Sabah, apparently trying to swim from Pulau Bai to the Sandakan side of the bay, 5 kilometers away. Periodic influxes of large numbers of bearded pigs to Sibutu Island in extreme S.W. Philippines, were almost certainly linked to periodic population increases and migrations of Bearded Pigs on mainland Borneo (Sabah), given numerous, apparently reliable, accounts of wild pigs crossing the channel between Sabah and Sibutu, where they have sometimes been killed by fisherman. On one occasion, a large number of swimming animals are reputed to have been used for target practice by a U.S. Navy battleship, which encountered them whilst on patrol. In any event, water obviously is hardly a barrier to these animals, even if their target direction is far away and maybe not even visible.

Breeding. Age at first pregnancy varies in the wild from about 10–20 months. The rut appears to coincide with synchronized flowering in the forest, with the timing being centered on the transition between late flowering and early fruit formation. Falling petals therefore offer a potential visual cue. During the onset of droughts and related flowering of dipterocarps, Bearded Pigs rut and construct nests. In big fruiting years, Bearded Pigs can “double-clutch”. This suggests that a certain nutritional status may have to have been attained by females before they become responsive to whatever stimulus acts to trigger mating. Pregnant females had a median fatness index (finger-widths of fat depth at the shoulder) of 1.5, while rutting males scored zero by this measure (n = 19, 32). Gestation length is estimated at 90–120 days, based on the interval between rut and the ensuing birth-peak. Birth occurs within a nest, which is constructed of vegetation by the mother, and which is occupied by her and the new piglets for a week or so. Data from hunter interviews indicated that the median number of piglets accompanying an adult female (n = 53) was 7, which was the same as the median number of fetuses counted in dead females (n = 8). Litter size is, however, very variable in part because of the influence of female size: small mothers typically have 3–4 piglets in a litter, while large ones have 10–12.

Status and Conservation. Humans have lived in Borneo for at least 40,000 years and have been hunting mammals such as Bearded Pigs for at least 35,000 years. Holocene and pre-historic cave finds in Sabah, Sarawak, and East Kalimantan indicate that Bearded Pigs have been the most commonly hunted Bornean mammal for at least the last 15,000 years. The archaeological evidence suggests that the Bearded Pig was hunted but apparently fairly plentiful and widespread in the Malaysian Peninsula and Sumatra about 1,500 to 2,000 years ago. Over-hunting has since led to population declines, and in some parts of Malaysia, Sumatra, and Borneo, Bearded Pigs had already been hunted to near extinction by the 1920s. More recently, this is becoming a reality for many more parts of their range, where over-hunting, logging and conversion of forests have caused a rapid decline in Bearded Pig populations. Over-hunting has also likely led to the extermination of many of the small island populations from which the species was historically known. In 1906, such extinctions were reported for the Penata and Kebun Islands in the Burung group of northern West Kalimantan, but presumably further extinctions have occurred in the often densely settled islands where Bearded Pigs used to occur.

Sus barbatus is listed on The IUCN Red List as Vulnerable, mostly because of the rapid loss of its forest habitat and high hunting pressure throughout its range. It has been estimated that hunters in Sarawak take an annual harvest of up to one million or more pigs, making wild pork meat of considerable economic significance. This is quite often related to commercial timber extraction. One typical logging camp in Sarawak killed as many as 880 pigs per year, mainly for food. Hunting in these camps was found to be wasteful, with species being killed on sight even if the worker did not need the meat. In one logging area, for example, during a pig migration, people would kill an animal, take only the prime cuts of meat, leaving the rest to rot, and kill another animal the next day. These animals are by far the most preferred species of wild meat throughout Sarawak and Sabah, where they have comprised as much as 72% of the dressed weight of all animals hunted. In these areas, the impact of hunting on Bearded Pig populations seems clear, with a significant correlation between hunting pressure and animal density. This pattern is so strong that hunting pressure overrides the large effects of habitat variables and is the single main determinant of animal density in an area. As hunting pressure increases, the density of all animal groups investigated, including Bearded Pigs, decreases until, at high hunting pressure, all large animals are locally extirpated. These patterns of high hunting pressure on these animals are also found among Penan and Kenyah tribes in East Kalimantan, where pigs contributed 79.8% of all catches and 91% of all the edible meat. On average these people consume of 133.6 kg of pig meat per person per year, which is considerably higher than the estimate for Sarawak of 12 kg of pig meat per person per year.

In Peninsular Malaysia, the more sedentary population of Bearded Pigs, apparently associated with continuously-fruiting, Koompassia-Burseraceae forests, is endangered by hunting as well as habitat destruction. The habitat changes experienced on the peninsula since the Second World War have almost certainly favored Eurasian Wild (or ‘banded’) Pigs (S. scrofa vittatus) over Bearded Pigs in those parts of Peninsula Malaysia and Sumatra where sympatry between these species occurs. This poses a further, and potentially serious, threat to the latter species. In any event, available data indicate that wherever these two species are sympatric (not necessarily syntopic), the number of Eurasian Wild Pig is greater than the number of Bearded Pigs, and that Eurasian Wild Pig now has a much wider range of distribution than Bearded Pigs throughout these regions.

In Sumatra, habitat disturbance has been at least as extensive as in Malaya. A comparison between the current distribution of Bearded Pigs and that of the remaining native forest supports the contention that the species cannot long survive the reduction and fragmentation of these habitats. The same situation probably applies to Bangka and the Riau Archipelago where habitat disturbance has been at least as extensive as in Sumatra, and where the continued survival of the species is not clear.

These animals are also potentially threatened by various contagious diseases. For example, a rinderpest epidemic that killed a large proportion of the domestic cattle population of Southeast Borneo between 1871 and 1872, evidently spread to both domestic pigs and wild Bearded Pig populations over large parts of Borneo. Several similar and successive outbreaks amongst domestic cattle of rinderpest between 1878 and 1894 also killed off large numbers of these animals; perhaps the most serious being an epidemic in 1894 when populations of these animals had already been severely reduced by preceding epidemics in central Borneo in 1888 and 1889. A final epidemic occurred in 1906, when very many Bearded Pigs succumbed to a contagious disease in the Tabalung area in South Kalimantan. There are no recent records of such epidemics, but the proximity of domestic animals to remaining Bearded Pig populations is a potentially serious threat, particularly at times when these may already be nutritionally stressed. 



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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