Pigs

(Suidae)

Class Mammalia

Order Artiodactyla

Suborder Suiformes

Family Suidae

Thumbnail description
Medium-sized omnivores, characterized by elongated head and discoid snout, bristly pelage, tusks, and short tail

Size
34–83 in (86–211 cm); 77–770 lb (35–350 kg)

Number of genera, species
5 genera; 16 species

Habitat
Grassland, forest, steppe, desert, swamp, and agricultural fields

Conservation status
Critically Endangered: 2 species; Endangered: 1 species; Vulnerable: 2 species; Data Deficient: 1 species

Distribution
Global, in association with humans; all continents, except Antarctica

Evolution and systematics

The family Suidae is one of three extant families belonging to the suborder Suiformes that has its origins about 48 million years ago (mya) in the middle to late Eocene. The Suiformes (pigs, peccaries, and hippopotamuses) are anatomically the most primitive among the Artiodactyls, being characterized by having simple stomachs, many low-crowned, bunodont teeth, and a less-advanced unguligrade limb structure.

During the Eocene epoch 60 mya, there were giant pigs (entelodonts) that may have been distant relatives of today's pig; however, there is no evidence of a direct lineage. Paleontological evidence suggests that the origin of the pig is in the Miocene about 40 mya. At this time, their distribution was restricted to the Old World, and there is not any evidence that North America was the site of origin for any modern genera. The African suids underwent a major radiation during the Pliocene and early Pleistocene epochs, with approximately 17 species known from the fossil record; most of this diversity had disappeared by the mid-Pleistocene. The African suid radiation has served as a useful tool in reconstructing hominid paleoecology because hominids and suids had some ecological characteristics in common. In addition, there are many suid taxa that appeared, evolved, and disappeared in a relatively short period of time in Africa, making them useful markers in biostratigraphy for aging archaeological sites. It has also been suggested that Pleistocene suids competed with Homo erectus for subterranean food sources.

The genus Sus is thought to have originated at the latest in the Miocene or near the Miocene/Pliocene boundary, 5 mya. Genetic studies suggest that the origin of the babirusa (Babyrousa babyrussa) is between two and 10 mya, and that of the warthog (Phacochoerus africanus), between five and 15 mya; these estimates are approximately 50% more recent than those suggested by paleontological and anatomical data. The only babirusa fossils to date are from the Pleistocene, and known fossils of the warthog are no older than two million years.

The 1993 action plan of the IUCN/SSC Pigs, Peccaries, and Hippo specialist group recognizes three subfamilies of Suidae: the Suinae, or true pigs, the Phacochoerinae (warthogs), and the Babirousinae (babirusa). The Suinae comprises three genera (Sus, Potamochoerus, and Hylochoerus) and 11 species. The Phacochoerinae includes two extant species (P. aethiopicus and P. africanus), and the Babirousinae includes one species (Babyrousa babyrussa). However, recent reports by Groves in 2001 and 2002 suggest that some previously identified subspecies may in fact warrant full species status. Anatomical studies suggest that there may be as many as 40 subspecies within the Suidae. Approximately 16 more or less distinct subspecies have been found in the Sus scrofa lineage.

Physical characteristics

The Suidae are medium-sized mammals with stocky, sometimes barrel-shaped, bodies. Body weight ranges from 77 to 770 lb (35–350 kg) and may be as high as 990 lb (450 kg) in some domesticated breeds. The length of the body is 34–83 in (86–211 cm), while body height is 21–43 in (53–109 cm). The exception is the pygmy hog (Sus salvanius), which is only 20–28 in (51–71 cm) in length, 10–12 in (25–30 cm)

in height, and 14.5–21 lb (6.5–9.5 kg) in weight. The neck is short, whereas the head is long and pointed with a mobile snout. The tip of the snout is cartilaginous and discoid. The eyes are fairly small, and the ears are generally long, with a tassel of hair at the end in some species. The first digit is absent. Each foot has four digits, the middle two of which are

flattened and bear hooves. The outer digits are higher up the leg and bear smaller hooves.

The complete dental formula is 44 teeth (3143/3143 per quadrant) in Sus, Potamochoerus, and Hylochoerus, while Babyrousa and Phacochoerus have 34 teeth (2123/3123 and 1133/3123, respectively). The upper canines are large and curve upward, protruding from the mouth to varying degrees. The exception is the babirusa, in which the upper canines protrude upwards through the skin of the head, never entering the mouth. The lower canines are generally sharper and may or may not be visible outside of the mouth. Suids have a simple, non-ruminating stomach composed of two chambers.

Skin color varies greatly in the suids, from brown to almost black, whereas the pelage may be dark gray or black to light red and of varying length. Some babirusa appear almost naked. Some species have a mane or dorsal crest of hair. The male Visayan warty pig (S. cebifrons) bears a long mane that is shed after the breeding season. In many species, the young bear stripes. Some members of the Suidae bear warts or fleshy ridges on the face. These are fleshy structures with no bony core or support. Females have from two to four pairs of mammae.

Distribution

Today, wild suids are found on every continent, except Antarctica, as well as on many oceanic islands. Their presence in the New World and on some islands (e.g., New Guinea, New Zealand, and possibly Madagascar) is due to introductions by humans. The domesticated pig has a global distribution due to its association with people, and has returned to a feral state in some areas (e.g., North America). The historical range of the Suidae was restricted to the Old World. Wild pigs occurred throughout much of sub-Saharan Africa, Europe, Asia, Asia Minor, India, and the East Indies as far southeast as the Philippines and Sulawesi. The ranges of many species have decreased in modern times because of expanding human populations and the associated loss of habitat and hunting pressure. In some cases, and for some species (e.g., wild boar), the conversion of land for agriculture has benefited local populations of wild pigs and allowed them to expand their range.

Habitat

The wild suids are found in a diverse array of habitats ranging from semi-arid environments and temperate woodlands to tropical rainforests and swamps. They also often take advantage of agricultural lands. They occupy altitudes ranging from sea level to over 13,000 ft (4,000 m). Habitat selection is dictated by the availability of energy-rich foods, climactic extremes, and predation pressure. Some species may occupy a range of habitat types as long as they have adequate food resources (e.g., wild boar), whereas others specialize on a particular habitat (e.g., pygmy hog). Forest type, elevation, and forest age have been found to influence habitat selection in some populations of wild boar. It has been suggested that wild pigs play an important role in forest diversity, regeneration, and structure through their depredation of seeds and young saplings. Studies of the effects of wild pigs on the environment

have had varying results. Wild pigs may increase or decrease forest species' richness, negatively impact regeneration of trees, remove competitive vegetation such as weeds, and decrease soil macroinvertebrate populations. There is also evidence the Eurasian wild pigs will take advantage of acorn caches created by small mammals.

The suids can be divided into two groups in terms of territoriality or home range use. The African suids are generally more sedentary than other wild pigs, occupying small territories or home ranges that may overlap. The other suids are also more or less sedentary, but changing ecological conditions may cause these species to roam in search of better places to forage, sometimes over long distances. Whether territorial or not, areas occupied by wild suids tend to have several features in common. Resting places are one such feature, and these tend to take the form of nest sites or burrows. Most wild suids construct nests for farrowing, whereas others build nests for protection in bad weather (e.g., P. larvatus), but some construct nests all year round (S. salvanius). Most wild suids make nests of varying complexity and structure, using vegetation. Nests may be used year round or seasonally. Warthogs often occupy burrows dug by aardvarks (Orycteropus afer) and do not build their own nests. Wild suid home ranges also include tree trunks, rocks, or anthills that are used as spots for rubbing and scratching the body. These home ranges also include sources of shade and water, as well as mud wallows. These features are of critical importance as some suids do not have functional sweat glands for cooling the body. In forest hogs and warthogs, traditional defecation sites have been reported. Finally, all home ranges include sites for foraging. These features are often connected by a well-worn set of trails. Home range size fluctuates in response to food availability, reproductive condition, population density, age, and sex. Home ranges of 125–965 acres (52–390 ha) have been reported for wild boar.

Behavior

Suids are generally characterized by a loose social organization in which the basic unit is the mother-offspring pair. Group sizes vary from one to 15 individuals. Females may live alone or in groups with other females called "sounders." Offspring may remain in the natal group up to two years. Natal males almost always disperse, whereas natal females may sometimes remain in the group permanently. Males associate closely with females only during the breeding season; however, the African suids differ in this regard. Male forest hogs live with family groups year round, and male bush pigs associate with females longer to help rear the young. Male warthogs join females for breeding, leave, and then return after the young are born. Group size sometimes increases in proximity to fixed resources such as saltlicks or in response to availability of resources. Large groups may sometimes split into smaller ones if hunting pressure is high. Territorial or home range marking has not been well documented, but it has been suggested that the plowing behavior of babirusa may have a scent-marking function. The tusk gland has also been suggested to play a role in territorial marking. Phermones produced in the salivary glands of boars have been shown to induce standing in estrous females.

Suids communicate using a variety of sounds and displays. Vocalizations are used to convey fear, pain, comfort or well being, warning, or for breeding and establishing contact. Olfactory investigation of the snout and genitals are common features of greetings in wild pigs. Displays are often used in aggressive encounters but also during courtship and breeding. When displays fail to diffuse aggression, body contact is made. Several combat postures have been noted, including "boxing" on the hind limbs in babirusa. Wild pigs are fast runners and good swimmers. They will generally flee when threatened, but they will fight vigorously when they are wounded or cornered. The upper and lower tusks are formidable weapons in some species. There has been some suggestion of a dominance order both within and between the sexes among babirusa. Cannibalism and infanticide have been observed in some species. Solitary, social, and object play behavior have been documented in wild piglets.

The warthog is diurnal, but other wild pigs are often more active at night or at dawn and dusk. They generally become more nocturnal when hunting pressure is high. They may be active 40–65% of the time. There is a tendency for there to be two peaks in activity; however, this is affected by climate, reproductive condition, and resource availability.

Feeding ecology and diet

Wild pigs are usually omnivorous, consuming diets of leaves, grasses, young saplings, seeds, roots, tubers, fruits, fungi, eggs, invertebrates, carrion, and small vertebrates. The suid diet fluctuates considerably during the year to take advantage of energy-rich foods such as fruits and acorns. Most species also visit mineral licks where they ingest soil or water. Warthogs will chew animal bones, possibly as a source of calcium and other minerals. Wild pigs are known for their rooting behavior, but the extent to which they do so depends on the species and the soil conditions. The babirusa lacks a well-developed rostral bone and so can only root in very soft, moist soils. Warthogs,

on the other hand, have a very strong rhinarium and will go down on their wrists to dig in the hard soil to excavate roots and tubers. Pigs will forage alone or in small groups, though in some cases they will form very large groups to feed on ephemeral resources. Bearded pigs (S. barbatus) have been known to form groups of hundreds of individuals and make mass migrations following the fruiting of dipterocarps. These migrations occur over a period of months during which the animals may travel 150–400 mi (250–650 km). Aggregations of 30–60 red river hogs (Potamochoerus porcus) have been observed in Guinea and eastern Democratic Republic of the Congo (Zaire). Studies of Eurasian wild pig and bearded pig suggest a strong link between nutritional status and reproduction in these species. The populations of both of these species will increase dramatically following mass fruiting events. Alternatively, populations will decline significantly in drought years.

It has been argued that wild suids play a significant role in forest structure. A study in Queensland, Australia found that the germinability of mesquite seeds (Porsopis pallida) remained very high after passing through the gut of wild boar, suggesting that wild pigs may be important agents of seed dispersal. Exclosure studies in Malaysia have demonstrated that soil rooting and seed predation by Eurasian wild pigs decrease stem density and species richness; however, other studies have concluded that the foraging behavior of wild pigs may increase species richness in forests. The amount of rooting pigs do depends on food availability. In the temperate zone, most rooting occurs in mid-autumn to spring. After this period, rooting decreases as pigs switch to foraging on herbs and foliage.

Reproductive biology

Suid reproduction differs from that of other ungulates in several ways: the gestation is relatively short, newborns are very small compared to the mother, suids are the only truly multiparous ungulates, and all show nest-building behavior prior to parturition. In some species, the young are unable to regulate their body temperature and, also in contrast to many other ungulates, mothers nurse from a recumbent position as opposed to standing. In most suids, males associate with females only during estrus. The mating system is generally polygynous, but there has been some suggestion of monogamy in warthogs.

Estrous females urinate more frequently than usual, and the voided urine is sniffed and sometimes licked by males. Courtship behavior includes broadside displays, chasing, vocalizations, female solicitation of the male, and male nuzzling of the sides and vulva of the female. Female estrus is accompanied by swelling of the labia and mucus discharge. Males also tend to salivate excessively during this time. There may also be mutual grooming of the genitals. There are multiple mounts before intromission, and copulation sessions may last from 15 to 30 minutes. Adults will copulate several times per day. The estrous cycle is 21–42 days in length, with estrus lasting one to four days. Gestation lasts 100–175 days, depending on the species. In some species, sexual maturity is reached as early as eight months whereas in others, maturity is attained at two to five years of age.

Prior to parturition, sows will separate from their sounders, if they live in one, and construct a nest in which to give birth. Nests are usually located in thick cover. Females may excavate a shallow area and line it with vegetation or create a bed of vegetation on which to farrow. Babirusa sows often farrow at night in captivity. In domestic pigs, the mother does not help free the young from membranes and usually does not eat the placenta. Litter sizes in wild pigs vary from one to 12 piglets, with litters of babirusa and Visayan warty pig having the smallest litters (one to three piglets). In domesticated pigs, litter sizes generally increase with age and depend on breed and may reach 18 piglets. Piglets will compete among themselves to establish a teat order shortly after birth and will nurse from the same teat throughout lactation. In domestic pigs, sows may nurse up to 20 times per day, and they wean their litters at eight to 14 weeks of age, whereas bearded piglets are weaned at five or six weeks, and babirusa piglets are weaned at 26–32 weeks. Piglets may leave the nest with their mothers as early as a few days postpartum. Males generally provide little, if any, parental care, but may defend the young in some species. Females will vigorously defend their young and will sometimes work with other females to repel predators.

Reproduction in the temperate zone is generally seasonal with parturition occurring in spring and mating in autumn or winter; however, these periods are variable and seem to be dictated in large part by food resources. Drought conditions tend to decrease the percent of adult females that breed in a given year. Similarly in the tropics, reproduction can

occur year round when the availability of energy-rich foods is high. Studies in the Cape Provinces have shown that life history characteristics reflected differences in nutrient availability. Bush pigs (P. larvatus) in the eastern areas of the Province had a higher quality diet and showed a higher reproductive investment (e.g., small, young females had large, frequent litters with low survival rates). Southern bush pigs bred at a later age and larger size, and their litters were smaller and had higher survival rates. In Borneo, female bearded pigs appear to require a certain thickness of subcutaneous fat in order to be responsive to mating stimuli. In this species, young born to fat mothers grow and mature quickly and can breed within one year. Among domestic pigs, it has been shown that nutritional status can affect hormone secretion and fertility.

Conservation status

Though some species of wild pigs are very widespread and abundant, others are Critically Endangered with very limited distributions. According to the 1993 Survey and Action Plan of the IUCN/SSC Pigs, Peccaries, and Hippos Specialist Group, the pygmy hog is considered Critically Endangered. Indeed, its distribution is now restricted to only one national park in Assam. The common warthog is still considered to be secure, but the remaining desert warthog subspecies (P. a. delamerei) is considered Vulnerable. The forest hog is considered Rare to Endangered depending on the subspecies. Bush pigs and the red river hog are still considered widespread and abundant, or secure. The majority of subspecies of Eurasian wild pigs are also considered widespread and secure; however, the subspecies S. s. riukiuanus from the Ryukyu Islands in southern Japan is considered Vulnerable to Endangered. The bearded pig is considered potentially at risk or rare, as is the Philippine warty pig (S. philippensis). Javan warty pigs (S. verrucosus) are considered Vulnerable, and the Visayan Warty pig is Endangered, perhaps critically. The babirusa is Vulnerable or Endangered, whereas the other species sharing its range, the Sulawesi warty pig (S. celebensis), is still considered Secure. The Vietnam warty pig (S. bucculentus) is known from only a few recent skulls and may be extinct. The babirusa and pygmy hog are listed on Appendix I of CITES and are both considered Endangered by the United States Fish and Wildlife Service. Babirusa are protected under Indonesian law, and the pygmy hog is on Schedule 1 of the Indian Wildlife Protection Act of 1972. Forest hogs are listed on Class B of the African Convention on the Conservation of Nature and Natural Resources. The babirusa is endemic to the island of Sulawesi. In terms of species diversity and endemicity of wild pigs, the Philippines is the most important country in the world. Of the three species known in this area, two are endemic (S. philippensis and S. cebifrons). Seven subspecies are recognized, and six of these are endemic. More taxa await description as well.

The main threats to wild pigs are hunting and loss of habitat. For some species such as the Visayan warty pig, hybridization with local domesticated, feral, or wild stock of S. scrofa represents a major concern. The only way to ensure the survival of the Visayan warty pig at this point is captive breeding of pure stock. The conversion of forests to agricultural land has in some places benefited local populations of wild pigs, but in general the impact is negative, especially for forest specialists like the babirusa. Hunting generally take ones of three forms: subsistence hunting, commercial hunting, and hunting in reprisal for crop damage. Subsistence hunting is often not a significant threat for any of the wild pigs, but is being overrun in many places by a thriving market in bush meat. Some wild pigs are protected under law; however, enforcement is nonexistent in many cases. A disturbing development in the eradication of pigs as crop pests has been the use of "pig bombs," small vessels of gunpowder placed on or in the ground that explode when pigs root or chew them. Though a couple of species are listed by CITES, trade is not a significant threat for wild pigs. Population estimates for wild pigs are difficult to obtain given the types of habitats they prefer, their shy, reclusive nature, and nocturnal habits.

As of 2003, much of the conservation work being done on wild suids involves population surveys and habitat assessment as well as basic studies of behavior and ecology, though integrated conservation programs have been developed by the IUCN Pigs, Peccaries, and Hippos Specialist Group for both pygmy hogs and Visayan warty pigs under the aegis of formal agreements with the relevant national governmental authorities. There has also been a number of studies of local markets to assess the extent of the bush meat trade in wild pigs. For some wild pigs, population models have been developed to determine what sustainable levels of harvest may be. Public education campaigns have been launched in some areas to inform people that the wild pigs living around them are threatened with extinction. Some educational initiatives have also been aimed at reducing human-pig conflict. Captive

breeding programs for pygmy hog, Visayan warty pigs, and babirusa have been initiated in their countries of origin; the latter two and some others are also being bred in the United States, Europe, and elsewhere. In some cases, these populations are very inbred because of small numbers of founders. Health regulations on imports of swine and other ungulates, coupled with historically little interest in suids as zoo exhibits, have contributed to this problem.

Significance to humans

Wild pigs represent either a pest or an important source of dietary protein for most humans. In places where they co-occur with people, pigs frequently do serious damage to agricultural lands through their consumption of crops and/or rooting behavior. They have also been known to do serious damage to timber plantations. Thus, they are often persecuted in reprisal for losses. However, even in areas dominated by Islam or other religions that forbid the consumption of pork, pigs are very frequently hunted for their flesh. Pigs represent a valuable resource for both subsistence and commercial hunting throughout much of their range in Asia and parts of Africa. In some areas wild pigs may be vectors of diseases that pose threats to domestic livestock. Some pig cultures still exist wherein pigs are valued as commodities, used as currency, or have ritualistic significance; however, these cultures are becoming more rare.

The earliest domestication of the pig appears to have taken place in Anatolia, Mesopotamia, and northern Iraq approximately 9,000 years ago. The domesticated pig came to Europe via the Caucasus and Balkans and is found in Aeneolithic and Bronze Age burials. The turbary is thought to be a transitional form between the wild boar and domestic pig. However, there is some evidence that other species besides S. scrofa

were used as stock for domestication (e.g., S. celebensis in Southeast Asia). Local wild boar populations no doubt contributed to local breed development in Europe; however, Asia was the primary center of domestication, and many of today's European breeds are influenced by Asian stock. The skull of the domestic pig has changed from its wild form more than that of any other domesticated animal besides the dog. The skull is now broader, with a shortened anterior portion. The brain case is also higher. Other characteristics of this domestication include a larger body, smaller head, longer body, and shorter legs, the existence of flop ears, and a curly tail. In modern times, the major centers of domestic breed development have been England, China, and the United States, though several countries in Europe developed their own localized breeds, known as landraces. There are approximately 175 breeds and types recognized around the world. Some breeds are threatened with extinction or considered endangered, mainly because of declining popularity and changes in consumer demands (e.g., leaner pork). The American Livestock Breeds Conservancy lists nine suid breeds as critical or rare, and the Rare Breeds Survival Trust in Britain maintains populations of seven breeds of concern.

The pig is unique among domestic animals in that it has become widely used as an animal model in biomedical research given its similarity to humans in certain aspects of its anatomy, physiology, and even behavior. One of the most active areas of research involving pigs is xenotransplantation. Pigs represent a good source of organs owing to their size, availability, and limited risk of zoonosis. Potential donor organs for human recipients include porcine heart, kidney, liver, heart-lung, and pancreas tissue. Research is needed to overcome some of the immunological barriers before widespread use of porcine organs is possible; however, selective breeding and genetic engineering are also being explored as methods to reduce transplant rejection.

Species accounts

List of Species

Forest hog

Hylochoerus meinertzhageni

subfamily

Suinae

taxonomy

Hylochoerus meinertzhageni Thomas, 1904, Kenya. Three subspecies: West African forest hog (H. m. ivoriensis), Congo forest hog (H. m. rimator), and giant forest hog (H. m. meinertzhageni).

other common names

French: Hylochére; German: Riesenwaldschwein; Spanish: Hilóquero.

physical characteristics

Length 51–83 in (130–210 cm); height 30–43 in (76–110 cm); males 506.5 lb (230 kg) (range 319–606 lb [145–275 kg]), females 397 lb (180 kg) (range 286–449 lb [130–204 kg]). The pelage is sparse and composed of long, coarse, dark hairs. The skin is slate to blackish gray. Young are straw colored and lack stripes. Patches of skin anterior to the eyes are relatively hairless and form large protruding cheek pads in males. The snout is large and discoid in shape. Tusks are smaller than in the warthog (12 in [30 cm] or less). There are 32–34 teeth. Females have four pairs of mammae.

distribution

Found in a variety of forested habitats across western, central, and east tropical Africa.

habitat

Elevations to 12,500 ft (3,800 m), subalpine forests, bamboo groves, montane, swamp, and gallery forests, savanna-forest mosaics, and wooded savannahs. More likely to occur in areas with permanent water sources, thick understorey vegetation, and a variety of vegetation types. Does well on habitat edges.

behavior

Generally most active from dusk to midnight, but may also be diurnal in areas free of human persecution. The basic social group is a sounder containing one or more adult males, several adult females, and dependent juveniles or infants. These groups may sometimes form larger, temporary aggregations; however, males from different sounders are mutually intolerant of one another. Sounders have overlapping home ranges, with each range containing a network of well-worn trails to feeding sites, latrines, mineral licks, water holes for drinking and wallowing and sleeping sites. Home ranges may be up to 2.5 acres (1 ha) in size. Hyenas (Crocuta crocuta) and leopards (Panthera pardus) are the main predators.

feeding ecology and diet

Diet is mainly grass and dicotyledons in forested areas. Eggs and carrion may be eaten occasionally, while coprophagy and geophagy are common. Only root in soft soils.

reproductive biology

Polygamous. Male-male fighting is less ritualized than in some other African suids and often leads to serious injury and sometimes death. Breeding is generally continuous, but mating is often most frequent towards the end of a rainy season. Two distinct breeding seasons have been identified in the Virunga National Park in eastern Democratic Republic of the Congo (Zaire). Copulation may last up to 10 minutes. Sows give birth in sheltered nests lined with dry grasses after a gestation of about 151 days. The litter size commonly ranges from two to four but may reach 11 piglets. Piglets remain in thick cover for about seven days, but then accompany the sow. Young are weaned at nine weeks and attain adult body size by approximately 18 months. Females may disperse from the natal group and conceive at one year of age, while males remain in the natal group until secondary sex characters such as cheek pads develop.

conservation status

Main threats are excessive hunting and habitat destruction. Deforestation is particularly problematic in western Africa. Hunting pressure varies in intensity according to local religious beliefs or superstitions, but subsistence hunting is not thought to pose a serious problem. Commercial hunting is a serious problem in cities with surrounding forested areas. Forest hogs may also be eradicated in response to crop raiding. Population trends across its range are unclear in many cases. Not listed in CITES, but the West African forest hog is considered vulnerable by the IUCN.

significance to humans

Like other African suids, the forest hog is a significant source of meat for subsistence or commercial purposes. Certain tribes use the hides for war shields, while others superstitiously avoid killing them altogether in order to avoid trouble.

Bush pig

Potamochoerus larvatus

subfamily

Suinae

taxonomy

Potamochoerus larvatus (Cuvier, 1822), Madagascar. Four subspecies: P. l. hassama from eastern Africa, P. l. koiropotamus from Angola and southeastern Africa, P. l. larvatus from Mayotte in the Comoro Islands and western Madagascar, and P. l. hova from eastern Magascar.

other common names

French: Potamochère; German: Buschschwein; Spanish: Jabalí de río.

physical characteristics

Length 39–59 in (100–150 cm); height 21.5–38 in (55–97 cm); weight 154.2 lb (70 kg) (range 101–286 lb [46–130 kg]). Snout is elongated. Animal ranges in color from light red to brown and gray to predominately black. Newborns are dark brown in color with rows of light spots. The tusks are least conspicuous among the African suids; the upper tusk averages 3 in (7.6 cm), whereas the lower tusks range from 3.5–6.5 in (9–16.5 cm) in length. Males have small warts in front of the eyes. There are six pairs of mammae.

distribution

Found from Somalia to east and southern Zaire down to the Cape Provinces in South Africa. It is also found on Madagascar and on Mayotte Island in the Comoros; however, it was most likely put here by humans.

habitat

Generally found in more moist habitats with significant vegetative cover and tend to avoid drier, more open areas. May occupy riverine, lowland, swamp, and montane forests as well as woodland savannas, scrub habitat, and cultivated areas.

behavior

Mainly nocturnal, sleeping in self-excavated burrows or in heavy thickets of vegetation during the day. Those living in the southern Cape tend to be more diurnal during the colder months, suggesting temperature regulation may be an important factor influencing the activity rhythms in some populations. They live in single male family groups containing one or more females and their young (group size range four to 15 individuals), though both species have been observed in larger herds. Family groups are territorial, similar to other African suids. Territorial encounters are often characterized by ritualized displays and scent marking. Territory sizes vary with location and range from 0.05–2.5 acres (0.02–1 ha). Adult males play a role in rearing and defending the young. Males disperse from the natal group, whereas females may remain on the natal territory.

feeding ecology and diet

Omnivorous, consuming roots, bulbs, fungi, fruit, eggs, invertebrates, birds, small mammals, and carrion. They use their snouts to root in the ground and can do serious damage to crops in a short time. Field studies in Uganda have found that bush pigs may follow groups of monkeys as they forage and feed on the discarded fruits.

reproductive biology

Polygamous. Reproduction is seasonal with young being commonly seen at the end of the dry season or beginning of the wet season. The average gestation is 120 days. Litter sizes range from one to six, with three to four piglets being the most common. Newborns weigh 24.5–28 oz (700–800 g). Females may start breeding at two to three years of age.

conservation status

The IUCN has designated this species as widespread and locally abundant or relatively secure, depending on the subspecies. Though the bush pig is still relatively widespread, its distributions are patchy in certain regions. They have been reported to be rare outside of protected areas, and they are widely hunted either for subsistence or for commercial sale of the meat at local markets. In some countries, poaching inside of protected areas is a serious threat. The clearing of some forested areas and conversion to cropland has benefited this species in some areas.

significance to humans

Notorious crop raiders. They are also sometimes thought to pass diseases on to livestock. Eradication programs for these species have been largely unsuccessful because they breed quickly and are cryptic in nature. Potamochoerus does represent an important source of meat for food or revenue in some places, while in others the meat is avoided because it is thought to transmit epilepsy.

Common warthog

Phacochoerus africanus

subfamily

Phacochoerinae

taxonomy

Phacochoerus africanus (Gmelin, 1788), Senegal. Four provisional subspecies: northern warthog (P. a. africanus), Eritrean warthog (P. a. aeliani), Central African warthog (P. a. massaicus), and southern warthog (P. a. sundevallii).

other common names

French: Phacochère commun; German: Warzenschwein; Spanish: Jabalí verrugoso.

physical characteristics

Barrel-shaped body 57–75 in (145–190 cm) in length, 25.5–33 in (65–84 cm) in height; males 180.5 lb (82 kg) (range 150–220 lb [68–100 kg]), females 143 lb (65 kg) (range 99–156 lb [45–71 kg]), mostly hairless except for a long, coarse mane of dark hair on the neck, shoulders, and rump, a tufted tail, white cheek whiskers, and some bristles scattered over the body. The skin is dark brown to black in color. Young are reddish brown. The head is large and flattened with one or two pair of warts on the face beneath the eyes and near the tusks. Both sexes have well-developed tusks. The upper tusks may measure 23.6 in (60 cm) in length, whereas the lower tusks are only 5.1 in (13 cm). There are 32–34 teeth, though old animals may be missing a number of teeth. There are four pairs of mammae.

distribution

Found in savannas in almost all sub-Saharan countries from Senegal and southern Mauritania to northern Ethiopia and Djibouti, south to Namibia, the Cape Province, and Natal.

habitat

Elevations to 9,840 ft (3,000 m), open and wooded savannas, grassy plains, and semi-arid areas.

behavior

Mainly diurnal. Males tend to live alone or in small, bachelor groups with changing membership. Males are not territorial and only associate with females for mating. Females live in sounders consisting of one to three females and their offspring. Females may remain in the natal group for several breeding seasons, whereas males disperse from the group but remain on the natal home range (67–1,194 acres [27–483 ha]), depending on locality. Lone males, bachelor groups, and several sounders may use the home range simultaneously; these individuals are collectively known as a clan. Warthogs take shelter in subterranean burrows, often excavated by aardvarks, at night. The main diurnal predators are lions (Panthera leo), leopards, cheetah (Acinonyx jubatus), and wild dogs (Lycaon pictus), though leopards and cheetah tend to prey on younger warthogs. Warthogs communicate using scent marks deposited by both sexes, though more frequently by males, and a number of visual displays and vocalizations.

feeding ecology and diet

Selective grazers whose diet consists of grass, roots, fruits and berries, bark, and sometimes carrion. Usually drink on a daily basis, but may obtain sufficient water from succulent roots and bulbs when water is scarce.

reproductive biology

Likely polygamous, but possibly monogamous. Males will fight among themselves for mating opportunities, sometimes inflicting serious wounds with their upper or lower canine tusks. Estrus in females is characterized by frequent urination and discharge from the swollen vulva. Copulation may last less than a minute. While warthogs may breed throughout the year in equatorial areas, breeding behavior and farrowing are seasonal in other areas and synchronized with the end and beginning of rainy periods, respectively. Females are seasonally polyestrous with estrus occurring about every six weeks and lasting approximately three days. The gestation ranges from 160–170 days, and the average litter is three piglets (range one to eight), each weighing 14–32 oz (400–900 g). Sows will leave their sounder temporarily to give birth in a hole in the ground. The sow rarely leaves the piglets during the first week and eats less than usual during the first several weeks postpartum. Piglets remain in the hole for six to seven weeks. The young may suckle 12–17 times per day, approximately every 40 minutes. The young may begin to graze on their own after two to three weeks and are fully weaned at six months. Both sexes reach puberty at 18 months, though males usually do not breed until about four years of age.

conservation status

Anthropogenic threats include over-hunting for meat and persecution in response to crop raiding, which may be a serious problem in some areas. Also viewed as competitors for forage on cattle ranches. Hunting pressure varies by region, often according to prevailing religious beliefs, and can cause a serious decline in numbers. Religious taboos relating to consumption of pork generally benefit warthog in Muslim areas, but they may still be hunted and the meat sold to other areas. There is also a small trade in warthog tusks, however not at an international level. Despite these threats, warthogs are considered widespread and abundant and their populations relatively secure, according to the IUCN. They are not included in the CITES appendices.

significance to humans

Represent either a crop pest or source of meat for subsistence or commercial trade, depending on the region. Commercial ranching and harvesting occurs in some parts of Africa (Zimbabwe, South Africa, and Burkina Faso).

Pygmy hog

Sus salvanius

subfamily

Suinae

taxonomy

Sus salvanius (Hodgson, 1847), Sikkim Terai, India.

other common names

French: Sanglier nain; German: Zwergwildschwein; Spanish: Jabalí enano.

physical characteristics

Length 20–28 in (50–71 cm); shoulder height 10–12 in (25–30 cm); weight 14.5–21 lb (6.6–9.7 kg). Aside from its smaller size, the only diagnostic characters of this species are its vestigial tail and the presence of only three pairs of mammae in females. This species has no facial warts. The hair is agoutibanded and medium brown along the sides of the animal, darkening along the back. Piglets are faintly striped at two to four weeks of age. The tusks of males are exposed, whereas those of females are not.

distribution

Now only found in a few isolated populations in Manas Tiger Reserve in northwest Assam, making it the rarest suid in the world.

habitat

Found only in tall grassland habitats associated with early successional riverine communities. Those grasslands dominated by Narenga porphyrocoma, Saccharum spontaneum, S. bengalensis, S. munja, Erianthus ravennae, Imperata cylindrica, and Themeda spp. are the most important for pygmy hogs.

behavior

The main social groupings are sounders containing one or more adult females and their offspring and solitary males.

Unique among the suids in that it builds nests year round, which are made of grass leaves and built over shallow depressions in the ground. Both sexes and all age classes use nests on a nightly basis.

feeding ecology and diet

Omnivorous, feeding on roots, tubers, grass leaves, shoots, fruits, seeds, insects, worms, eggs, and small vertebrates.

reproductive biology

Polygamous. Males will associate with estrous sows during the rut. Reproduction is highly seasonal with breeding beginning in late November and early December. Breeding may continue into the spring in captivity. Females are in estrus for three to four days during the 21-day cycle, and gestation lasts 120 days. In the wild, there is a clearly defined birth peak from April–June. Litters average around four piglets (range two to seven), weighing approximately 5.3 oz (150 g) at birth. Females are sexually mature at 20 months, whereas males reach maturity at two to three years of age. In captivity, both sexes reach sexual maturity at 10–11 months.

conservation status

Considered Critically Endangered by the IUCN and is listed on Appendix I of CITES, as well as on Schedule 1 of the Indian Wildlife Protection Act of 1972. Also considered endangered by the U. S. Fish and Wildlife Service. The main threats are loss and degradation of habitat because of human settlements, agriculture, flood control schemes, and improper management. Tree planting in grasslands and the use of fire to open up grasslands for new growth have been detrimental. Hunting is becoming more of a threat. The survival is closely linked to the existence of the tall, wet grasslands. A conservation program was launched in 1995 as a cooperative effort among the IUCN/SSC Pigs, Peccaries, and Hippos Specialist group, the Durrell Wildlife Conservation Trust, the Forest Department (Government of Assam) and the Ministry of Environment and Forests (Government of India), and includes captive breeding, field research, and reintroduction.

significance to humans

Though they are not crop pests, hunting of pygmy hogs for meat is increasing. Their small size makes it a potentially very useful and valuable genetic resource for biomedical research and further domestication.

Babirusa

Babyrousa babyrussa

subfamily

Babirusinae

taxonomy

Babyrousa babyrussa (Linnaeus, 1758), Borneo.

other common names

French: Babiroussa; German: Hirscheber; Spanish: Babirusa.

physical characteristics

May weigh 132–220 lb (60–100 kg), and measure 34–39 in (87–100 cm) in length and 25–32 in (65–80 cm) in height, depending on the subspecies. The length, thickness, and distribution of the pelage vary with location with some individuals appearing almost naked, while others have a long, coarse coat. Unlike most pigs, the young bear no stripes. The skin is brownish gray in color. The most striking features are the male's canines, which emerge vertically through the top of the snout and curve backwards toward the head. Females have two pair of mammae.

distribution

Endemic to the island of Sulawesi where it is still found in many areas. Also present on the Togian islands of Batudaka, Togian, and Talatakoh, the Sula islands of Mangole and Taliabu, as well as the island of Buru.

habitat

Are found in tropical rainforests, canebrakes, and on the banks of rivers and lakes where water vegetation is abundant.

behavior

Diurnal with a peak in activity in the morning hours. Females may live in groups with one to five other adult females and their young. Males tend to be solitary. The most frequent type of grouping seen at a natural saltlick was solitary males followed by single females with young, but groups as large as 15 individuals have been observed. Construct nests for sleeping and shelter from the rain. Adult females are dominant to sub-adult males but subordinate to adult males. Larger females are dominant to smaller ones. Predators include pythons (Python reticulatus and P. molurus), and possibly civets (Viverra spp.). Agonistic behavior takes the form of displays, body pushing and rubbing, as well as boxing. The lower tusks may be used for attack or defense, whereas the upper, protruding canines seem to be used to protect the face from the lower canines of opponents. It has been suggested that ploughing behavior, wherein the individual pushes its head into the ground, slides forward, and rolls from side to side, has a scent-marking function.

feeding ecology and diet

Omnivorous, consuming a diet of fruit, nuts, leaves, roots, and some animal material. Also consume soil and rock fragments at saltlicks. Roots only in very soft, moist soil because it lacks a rostral bone in its snout. In captivity, both sexes have been known to opportunistically cannibalize young. A unique feature of the digestive tract is a large area of mucous-producing cardiac glands that are thought to aid in fermentation.

reproductive biology

Females will give birth year round in captivity, but may do so less frequently in the wild. Sexual maturity may be attained at five to 10 months of age. The estrous cycle is 28–42 days, with estrus lasting one to three days. Males may mount the female multiple times before intromission, and copulation bouts may last 15–30 minutes; average copulation lasts three minutes. The reproductive lifespan of females may begin at one year of age and continue through age 14. The gestation period is 155–175 days (mean 163 days) and the usual litter is one to two piglets. In captivity, females often give birth at night. Females separate from the group to give birth in nests. Young are weaned at 26–32 weeks, though they begin to nibble solid foods at one week of age. Nursing frequency is highest in the first month postpartum and declines thereafter. The average nursing bout length is 10 minutes, longer than most suids.

conservation status

Considered Vulnerable or Endangered by the IUCN, depending on the subspecies, and it is on Appendix I of CITES. Designated as endangered by the United States Department of the Interior in 1980; given full protection under Indonesian law in 1931. The main threats are hunting, both commercial and subsistence, and loss of habitat. A 1997 census estimated that there were 5,000 babirusa remaining in the wild.

significance to humans

Most hunting activity is focused on the Sulawesi warty pig; however, babirusa are also taken as a source of protein. This species has not been reported to be a crop pest. Babirusa skulls are sold in local markets to tourists and in large department stores in Jakarta.

Eurasian wild pig

Sus scrofa

subfamily

Suinae

taxonomy

Sus scrofa Linnaeus, 1758, Germany. Sixteen subspecies, which can be divided into four subspecies groupings: the western (Europe, Africa), eastern (Mongolia, Far East), Indian, and Indonesian races.

other common names

French: Sanglier; German: Wildschwein; Spanish: Jabalí.

physical characteristics

Body weight ranges 77–770 lb (35–350 kg); however, some domestic breeds of this species may reach 990 lb (450 kg). Height ranges 22–43 in (55–110 cm). The pelage is coarse and is typically composed of short bristles of varying color over the entire body. Animal has no facial warts. Males have canine tusks, whereas the canines of females are smaller.

distribution

Found on all continents, except Antarctica, in wild or in a barely modified feral form. It also inhabits many islands.

habitat

Found in many types of habitat from semi-arid areas to tropical rainforests, including temperate woodlands, grassland, steppe, broadleaf forests, and agricultural lands.

behavior

Mainly diurnal, being most active in the morning and afternoon; however, they may shift to a more nocturnal activity pattern in disturbed areas or areas with significant hunting pressure. The basic social unit is a small group of females and their current litters. Adult males are solitary, and young from previous years are peripheral to the group. These groups may occasionally form larger (up to 100 individuals) aggregations. Home range size varies 48–4,950 acres (60–2,000 ha) across the species distribution in response to availability of resources, reproductive status, and hunting pressure. Active 40–65% of the time.

feeding ecology and diet

Omnivorous, with vegetable matter constituting about 90% of the diet. Consume roots, tubers, grasses, fruits, nuts, seeds, agricultural crops, soil, invertebrates, carrion, vertebrates, and mollusks. The composition of the diet shifts during the course of the year in many places in response to the fluctuating availability of energy-rich foods such as acorns. Animal has been known to migrate in response to food shortages.

reproductive biology

Polygamous. Puberty occurs between eight and 24 months. Age of first breeding is generally 18 months for females and five years for males. The estrous cycle is 21 days, with estrus lasting two to three days. Gestation averages 112–120 days, and the average litter size is four to six piglets, eight to 12 in domestic pigs. Breeding is generally seasonal, occurring mostly in the fall, but reproduction appears to be heavily dependent on the availability of food and, thus, body condition in females. Most births are in the spring. Females separate from their group to give birth and return later with their young. Births tend to be synchronous within social groups; however, during bad conditions often only the dominant female will give birth. Weaning occurs at three to four months of age.

conservation status

The IUCN has designated this species as widespread and abundant, known or believed relatively secure, or potentially at risk or rare, depending on the subspecies. The subspecies known from the Ryukyu Islands in southern Japan has been designated as Vulnerable by the IUCN. Most threatened by hunting and habitat destruction, but the survival of some subspecies is also threatened by hybridization with domesticated forms.

significance to humans

Consumed by humans more than any other species of suid and, in Asia, more than any other domesticated species. Represents a significant source of protein for subsistence and commercial hunters, and are persecuted in most of their range due to the significant damage they do to crops. Pig skulls and jaws are displayed as symbols of the hunter's ability and as protection from evil spirits. Some cultures use the intestines to read omens. In some island cultures, the domestic pig is treasured and has acquired significant cultural importance. Domesticated pigs may be used as currency for the payment of fines or fees for brides.

Resources

Books

Estes, Richard D. The Behavior Guide to African Mammals. Berkeley: University of California Press, 1991.

Oliver, William L. R., ed. Pigs, Peccaries, and Hippos: Status Survey and Conservation Action Plan. Gland, Switzerland: International Union for Conservation of Nature and Natural Resources, 1993.

Pond, Wilson G., and Harry J. Mersmann, eds. Biology of the Domestic Pig. Ithaca, NY: Cornell University Press, 2001.

Periodicals

Cosgrove, J. R., S. T. Charlton, S. J. Cosgrove, L. J. Zak, and G. R. Foxcroft. "Interactions between Nutrition and Reproduction in the Pig." Reproduction in Domestic Animals 30 (1995): 193–200.

Groves, C. P. "Taxonomy of Wild Pigs (Sus) of the Philippines." Zoological Journal of the Linnean Society 120 (1997): 163–191.

Organizations

The American Livestock Breeds Conservancy. P.O. Box 477, Pittsboro, NC 27312 United States. Phone: (919) 542-5704. Fax: (919) 545-0022. E-mail: albc@albc-usa.org Web site: <http://www.albc-usa.org>

Rare Breeds Survival Trust. National Agricultural Centre, Stoneleigh Park, Warwickshire, CV82LG United Kingdom. Phone: 024 7669 6551. Fax: 024 7669 6706. E-mail: alderson@rbst.demon.co.uk Web site: <http://www.rare-breeds.com>

Other

American Zoo and Aquarium Association, Pig and Peccary Taxon Advisory Group. <http://www.pigpectag.org>.

IUCN Pigs, Peccaries, and Hippos Specialist Group. <http://www.iucn.org/themes/ssc/sgs/pphsg/home.htm>.

Asian Wild Pig Research and Conservation Group. <http://arts.anu.edu.au/awpn/>.

David M. Powell, PhD