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Sus scrofawild boar

By Tanya Dewey and Jennifer Hruby

Geographic Range

Of all members of the pig family, Sus scrofa occupies the largest range. They originally occurred in Europe, Asia, North Africa, and the Malay Archipelago. Included in this native range were a number of island populations, including the British Isles, Corsica, Sardinia, Japan, Sri Lanka, the Ryukyu Islands, Taiwan, Hainan, Sumatra, Java, and smaller islands of the East Indies. Sus scrofa was later introduced throughout the world as domesticated animals by humans. Currently, Sus scrofa can be found nearly everywhere, from homes to barns to boggy marshes and mountainous terrain.

(Hopf, 1979; Storer, 1992) (Nowak, 1991)

Habitat

Although Sus scrofa is found in a wide variety of habitats as a result of domestication and introduction to new areas, the typical wild habitat is generally moist forests and shrublands, especially oak forests and areas where reeds are abundant. They are thought to be mainly limited by maximum winter snowfall, deep snow decreases their ability to travel and find food. They are sensitive to severe temperature changes. Sus scrofa has developed the technique of wallowing in mud or water to maintain a comfortable temperature. Wallowing also protects against sunburn and insect bites. Sus scrofa has even been known to wallow in their own urine to keep cool. Temperatures dropping below 50 degrees will cause discomfort. Conversely, Sus scrofa is prone to sunstroke in unusually warm temperature.

(Hopf, 1979; vanLoon, 1979; Storer, 1992) (Nowak, 1991)

Physical Description

Wild boars are covered in a scant coat of coarse, bristle-like hairs ranging from dark gray to brown. Head and body length ranges from 900 to 1800 mm, tail length is about 300 mm, and shoulder height is 550 to 1100 mm. Weight averages 50 to 350 kg, though some domestic breeds can attain weights of 450 kg. Males are generally larger than females. Wild boar have four continually growing tusks, one in each quadrant of the jaw. Females have 6 pairs of mammae.

Over the course of domestication Sus scrofa has developed varying skin colors, tail lengths, and snout shapes. Sus scrofa has varying ear shapes, ranging from small and erect to low-flapping. Sus scrofa is thought to represent the primitive condition of ungulates in that they have a comparatively simple digestive system.

(Hopf, 1979; vanLoon, 1979) (Nowak, 1991)

  • Sexual Dimorphism
  • male larger
  • Range mass
    50 to 350 kg
    110.13 to 770.93 lb
  • Range length
    900 to 1800 mm
    35.43 to 70.87 in
  • Average basal metabolic rate
    104.15 W
    AnAge

Reproduction

Mating season is a violent time, as males often fight for access to females. Male Sus scrofa are able to continuously sharpen their tusks by rubbing the lower ones against the upper ones. The tusks are used as weapons most frequently during mating season. Sus scrofa individuals develop thick tissue around the front of the belly to help protect against stab wounds from tusks. The most aggressive males have been known to secure as many as eight sows during a single mating season.

In temperate regions females give birth to one litter in the spring. In tropical regions breeding occurs year-round but is often concentrated during moist seasons. Females have an estrous of about 21 days and are receptive for 3 days. Young are born after a gestation period of about 115 days (range 100 to 140). Mothers give birth to litters of from 1 to 12 young, generally between 4 and 8. Although sexual maturity can be reached between 8 and 10 months of age, females generally don't breed until 18 months old and males do not generally reach the size necessary to compete for females until 5 years old.

(Hopf, 1979) (Nowak, 1991)

  • Breeding interval
    Females give birth to one to several litters in a year, depending on the region.
  • Breeding season
    Breeding season is dependent on regional climate.
  • Range number of offspring
    1 to 12
  • Average number of offspring
    4-8
  • Average number of offspring
    7
    AnAge
  • Range gestation period
    100 to 140 days
  • Average gestation period
    115 days
  • Average birth mass
    960 g
    33.83 oz
    AnAge
  • Range weaning age
    3 to 4 months
  • Average time to independence
    7 months
  • Range age at sexual or reproductive maturity (female)
    18 (high) months
  • Average age at sexual or reproductive maturity (female)
    8-10 months
  • Range age at sexual or reproductive maturity (male)
    60 (high) months
  • Average age at sexual or reproductive maturity (male)
    8-10 months

Female Sus scrofa give birth to their young in a nest constructed of grass. The young remain in the nest for some time after birth. Females are extremely protective of their young. Despite these protective measures, on average only half of a litter will survive to maturity, many fall prey to predators and disease. Young are nursed for 3 to 4 months and generally become independent before the next litter is born (up to 1 year). (Nowak, 1991)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan / Longevity

Wild pigs usually live to about 10 years old, although some have been recorded living as long as 27 years. Mortality in the young is high.

Behavior

Wild Sus scrofa in Europe are sometimes found in large herds ('sounders') of up to 100, though a more typical size is 20 individuals. Sounders are made up of females and their young. When males reach maturity they leave the group and live mainly on their own. Sounders may travel together over a large home range, but do not migrate. Wild pigs are generally active at dusk, dawn, and at night.

(vanLoon, 1979; Hopf, 1979) (Nowak, 1991)

Home Range

Studies of feral and wild S. scrofa in South Carolina and the Santa Catalina Islands (California) indicate home ranges vary from 100 to 400 hectares. Male home ranges are larger than those of females, often twice as large. Population densities in those areas and in North Carolina and Europe range from 1 to 34 animals per square kilometer. (Nowak, 1991)

Communication and Perception

Smell is by far the most advanced of the pig's senses. A large round disk of cartilage is connected to muscle that gives the snout extra flexibility. Sus scrofa also has an advanced sense of taste. They are quick to identify unknown objects with their sense of taste. It is believed that Sus scrofa lacks good eyesight. The eyes are positioned on the sides of the head, restricting their forward vision. Pigs also vocalize, consisting mainly of grunts and squeals. (Nowak, 1991)

Food Habits

Sus scrofa is known for its omnivorous and sometimes indiscriminate diet. The diet includes fungi, tubers and bulbs, vegetation, grains and nuts, fruit, eggs, small vertebrates, invertebrates, carrion, and manure. Such a wide range of food sources has enabled Sus scrofa to survive in a variety of environments, from deserts to mountainous terrain.

(Hopf, 1979; Storer, 1992; Porter, 1993) (Nowak, 1991)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • eggs
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • Plant Foods
  • leaves
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit
  • Other Foods
  • fungus
  • dung

Predation

The primary predator of mature wild pigs are humans. Mature pigs may also fall prey to very large predators, such as bears, large cats, and crocodiles. Young pigs may be preyed on by large snakes, raptors, cats, wolves, and other large predators. Pigs are extremely aggressive and bold when threatened. They use their ever-growing, sharpened tusks and the power of their bulk to charge and injure their attackers.

Ecosystem Roles

In ecosystems in which pigs are native, pigs contribute to the diversity of systems by disturbing the soil - creating areas for new plant colonization, and by dispersing fruit seeds. Pigs, especially the young, are also an important source of prey for large predators. In ecosystems in which pigs are not native, they are extremely destructive, outcompeting native pigs and peccaries, damaging native vegetation, and preying on native animals.

Economic Importance for Humans

Economic Importance for Humans: Positive

Pigs are an integrated part of the diets of numerous human cultures. Pigs mature faster than other domesticated ungulates, have larger litters, and can feed on human garbage, making them efficient and valuable parts of many agricultural systems. Humans have taken advantage of their acute sense of smell for a variety of tasks. For instance, they have been used to find truffles, underground fungi used in French cuisine. In ancient Egypt they were used for "treading the seed." Their hoofs created holes perfect in size and depth for planting seeds. The Egyptians exploited this ability and used Sus scrofa extensively during planting seasons. Wild pigs (boars) are also hunted for sport. Miniature breeds of domestic pig have become popular as pets.

(Hopf, 1979) (Nowak, 1991)

  • Positive Impacts
  • pet trade
  • food
  • body parts are source of valuable material
  • produces fertilizer

Economic Importance for Humans: Negative

Sus scrofa carries parasitic infections transmissible to humans through eating undercooked pork and through contact, including trichinosis, cysticercosis, and brucellosis. Both domesticated and wild pigs are also quite aggressive and a surprising number of injuries results from interactions with pigs, primarily in domestic settings.

Introduced, feral populations of Sus scrofa are responsible for tremendous environmental damage worldwide. Their broad dietary habits, extremely destructive behaviors, and aggression make them one of the most destructive introduced species across the globe. Wild pigs destroy native vegetation as they dig for food, travel in herds, and create wallows. They will eat native animals, such as ground nesting birds and their eggs. Wild pigs may also act as crop pests. (Nowak, 1991)

Conservation Status

Sus scrofa is not threatened in general. Populations of wild pig were exterminated through hunting from large parts of their native range, including the British Isles, Scandinavia, and Egypt. Reintroduction programs in Scandinavia seem to have been successful. Native pigs of the Ryukyu Islands (S. s. riukiuanus) are considered vulnerable as a result of excessive hunting. This subspecies is endemic to these islands, not an introduced feral population. There are numerous breeds of domesticated Sus scrofa, some of which seem to be in danger of disappearing and are the focus of domestic breed conservation efforts.

(Porter, 1993) (Nowak, 1991)

Other Comments

A symbiotic relationship between humans and pigs may have been what initiated their domestication, occurring as early as 10,000 B.C. in Thailand. Other sources place the time and place of domestication at 4900 B.C. in China. Sus scrofa may have used early gardens and garbage piles as food sources and humans took advantage of these pigs as a food source.

Sus scrofa has provoked mixed sentiments throughout history, from reverence to fear. In medieval Europe Sus scrofa was a popular carving in stone churches. They have also been regarded as a symbol of fertility and good luck. Others have not reacted so positively to Sus scrofa. Some saw the curly tail as connected to the devil. Jewish and Muslim traditions maintain strong taboos against the consumption of pork. Such adverse reactions may have originated because of the diseases associated with uncooked pork.

Domestic pigs are considered intelligent animals, more so than dogs. Circus trainers have characterized Sus scrofa individuals as quick learners with a substantial memory. Not only can they perform repetitive circus tricks, such as jumping through hoops and walking tightropes, but they can also solve simple problems such as opening a bolted door. Ivan Pavlov, the reknowned physiologist, first used pigs to perform some of his experiments, but eventually switched to dogs for reasons of temperament. It is also believed that Sus scrofa speaks a rudimentary language composed of calls, snorts, sniffs, and whistles.

Recently, Sus scrofa has been making the transition from an outdoor animal kept in the barn to an indoor pet. Miniature breeds have become popular pets.

(Hedgepeth, 1978; Hopf, 1979; vanLoon, 1979) (Nowak, 1991)

Contributors

Tanya Dewey (author), Animal Diversity Web.

Jennifer Hruby (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carrion

flesh of dead animals.

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

crepuscular

active at dawn and dusk

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

soil aeration

digs and breaks up soil so air and water can get in

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

Hedgepeth, W. 1978. The Hog Book. Doubleday & Company, Inc. NY.

Hopf, A. 1979. Pigs: Wild and Tame. Holiday House, NY.

Porter, V. 1993. Pigs - A Handbook to the Breeds of the World. Cornell University Press, NY.

Storer, P. 1992. Miniature Pigs. Barron's Educational Series, Inc. NY.

vanLoon, D. 1979. Small-Scale Pig Raising. Garden Way Publishing, Vermont.

Nowak, R. 1991. Walker's Mammals of the World, Fifth Edition. Baltimore, Maryland: The Johns Hopkins University Press.

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