The natural vegetation in all areas where bearded pigs are found is dominated by tropical evergreen rainforest, but within this broad category the animals utilize a wide variety of habitat types, ranging from beaches to upper montane cloud forests (Caldecott et al., 1993). The carrying capacity for bearded pigs no doubt varies greatly from habitat to habitat within the rainforest, depending on soil, drainage, elevation and floristic and phytochemical composition of the vegetation. Population density is also radically variable over time, so it is hard to determine consistent differences between habitats in this respect (Caldecott et al., 1993).

Bearded pigs consume roots, fungi, invertebrates in soil and rotting wood, small vertebrates, turtle eggs, carrion, and items from at least 50 genera and 29 families of plants. Fruit supply is believed to have particular influence in determining growth rate, fat deposition and reproduction, with the oil-rich seeds of members of the tree families Fagaceae (oaks and chestnuts) and Dipterocarpaceae (dipterocarps) being especially important in this regard. Of these, the oaks are significant because of their relatively continuous or regular fruiting behaviour, and also because they can come to dominate submontane habitats. The dipterocarps are often dominant in lowland and hill forests, and strongly influence food availability for terrestrial seed-eaters by characteristically synchronized flowering and mast-fruiting behaviour (Caldecott, 1988; Pfeffer, 1959; Pfeffer and Caldecott, 1986; Davies and Payne, 1982; Janzen, 1974; Jessup et al., 1982; Leighton and Leighton, 1983).

Large-scale population movements by bearded pigs have often been reported in Malaysia (Allen, 1948; Kempe, 1948; Hislop, 1949, 1952, 1955) and Borneo (Shelford, 1916; Banks, 1931, 1949; Banks in Hislop, 1955; Pfeffer, 1959; Davies and Payne, 1982; Caldecott and Caldecott, 1985; Caldecott, 1988a, 1991). Pigs are described as moving consistently in one direction, in scattered or condensed herds, over a broad or narrow front, and over a period of several days, weeks or months. The animals are variously described as being in good, poor or very poor physical condition, sometimes accompanied by piglets and sometimes not, and regularly swimming across rivers, sometimes coastal bays and even out to sea. In some cases, the population is said to retrace its route later, or to follow a circular course to return whence it originally came. The distances traveled appear to vary greatly. Pfeffer (1959) described annual, apparently unidirectional, population movements in Kalimantan involving distances of 250-650 km, while Davies and Payne (1982) refer to annual reversible movements over tens of kilometers in Sabah. The approximate population tracks given by Caldecott (1988a) suggest rates of travel of 8-22 km/month sustained over at least 4-8 months as part of larger cyclical movements in interior Sarawak. Some reports indicate that such population migrations begin or end in particular locations where abundant food may be found. Thus, Davies and Payne (1982) linked movements to seasonally-fruiting Dinochloa bamboo groves, while Caldecott (unpubl.) reinterpreted historical accounts so as to link Malaysian bearded pig movements with predictable fruiting in camphor wood (Dryobalanops aromatica) forests. Caldecott (1988a) also described what appeared to be regular use of fruiting montane oak (Lithocarpus) forests in the upper Baram area of Sarawak.

In Sumatra bearded pigs also exhibit large scale population movements, but reports are anecdotal and often contradictory. Groups of up to 300 individuals are said to embark on long migrations, arriving at a given location at irregular intervals, sometimes as often as once a year but more frequently once every two to four years. In the highlands these movements do not seem to have any relation to the seasons, but in the lowlands the pigs tend to move out of the inundated forests to higher ground in the rainy season and back again in the dry season (Blouch, 1984). The relationship between these movements and the cycles of mast production has not been investigated.

Bearded pig populations exhibit a range of different states, which can be summarized as follows:

1. Dispersed, static populations exploiting small, dispersed, unpredictable and discontinuous 'background' food sources. Low breeding and growth rates possible. Local movements only (e.g., typical mixed dipterocarp forest in Borneo between generalized fruiting episodes).

2. Small to medium populations exploiting concentrated, predictable and continuous 'target' food sources. High breeding and growth rates possible. Local movements only (e.g.. Koompassia-Burseraceae forest in Malaya).

3. 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 (e.g., typical mixed dipterocarp forest in Borneo between generalized fruiting episodes.

4. 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 (e.g., Dinochloa association in Sabah, or Dryobalanops aromatica association in Peninsular Malaysia).

5. 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 (e.g., interior of Sarawak in 1954, 1959, 1983 and 1987).

6. Very large and collapsing population having exceeded background food supply. Low breeding and high death rates. Increasingly desperate long-range movements (e.g., starving herds reported from Peninsular Malaysia and Borneo).

The basic social structure is that of the major social unit being 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. Age at first pregnancy presumably varies in the wild from about 10-20 months. In any one area, the rut coincides 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. 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 not known but 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). Abbot in Davies (1962) reported a slightly higher median of 9 fetuses per female (n = 5). Litter size is 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. Elsewhere, the range in litter size has been given as 3-11 piglets (National Research Council, 1983).

Fat reserves in the mother are used up quickly during lactation, and females accompanied by small piglets are almost invariably thin or very thin. Those with large piglets are fatter, and have presumably gained weight after weaning. This fattening process seems to depend on what fruit is available, with dipterocarp seeds and acorns having most impact. If these are abundant, it seems likely that two litters can be raised by a female within a year.