Wild boars (Sus scrofa) are a cosmopolitan species. They originated in Europe and Asia, but were widely introduced to North America and are considered an invasive species in the southeastern United States and California. They are common throughout Eurasia, and inhabit every continent except Antarctica. (Chapman and Trani, 2007; Oliver and Leus, 2008; Wood and Barrett, 1979)
Given their wide distribution, wild boars can be found in a variety of habitats. They may inhabit grassy savanna areas, wooded forests, agricultural areas, shrublands and marshy swamplands. They require a nearby water source and shelter (dense vegetation) to protect and conceal them from predation. They thrive in an assortment of climates, but generally avoid extreme heat or cold. In places that may experience harsh winter temperatures and increased snowfall, the population density may be limited by food sources. Deeper snows and frozen ground inhibit their ability to forage for roots and foliage. (Chapman and Trani, 2007; Melis, et al., 2006; Oliver and Leus, 2008)
Wild boars range from 153 to 240 cm in total length and weigh 66 to 272 kg as adults. Females tend to be smaller than males of the same age, with the size difference becoming more apparent as the animals age. Adult wild boars have a thick, coarse coat of hair covering their bodies. Their coat ranges in color from black to brownish-red to white. Depending on their geographic location, they can have a speckled or solid pelage color. They may also have longer bristly hairs that grow down the middle of their backs. At birth, young boars generally have yellowish-brown stripes running down their backs that disappear into an even coloration within about 4 months. Wild boars can stand as tall as 0.9 m at their bulky shoulders, tapering off towards their hind quarters. Their tails measure 21 to 38 cm, and their ears are 24 to 26 cm long. Their upper canine teeth typically measure 5 to 10 cm and are generally larger than their lower canines. Their upper canines are usually visible even when their mouth is closed. Their dental formula is I 3/3, C 1/1, P 4/4, M 3/3 = 44. (Chapman and Trani, 2007; De Magalhães and Costa, 2009; Ickes, 2001; Webster, et al., 1985)
Wild boars tend to live in large groups called sounders that are made up of 6 to 20 closely-related females, but may contain over 100 individuals. As the sows prepare to give birth, they temporarily leave the sounder and return with their young upon farrowing (giving birth to their litter). Even after reaching maturity, female piglets tend to stay in the same groups in which their mothers reside. These herds tend to have some overlap, and it is not uncommon for herds to split into subpopulations. Males stay with their mothers until they are 1 to 2 years old and then leave the herd. After departing, they generally only join a sounder during mating season. Polygynous males are attracted to groups of females that are in estrous. They become very aggressive and compete for the opportunity to breed with a sounder. Successful males chase females in estrous, nudging them to show their interest. If the female is also interested, she may respond by urinating. If the female does not urinate, the male may give up after several minutes. (Graves, 1984; Iacolina, et al., 2009; Oliver and Leus, 2008)
Wild boars are capable of reproducing at any time during the year. Mating is usually dependent on the climate, which can directly affect food availability. If the nutritional needs of the females are not being met, breeding can be suppressed. Females become capable of reproducing around the age of 10 months, and males are sexually mature at approximately 5 to 7 months. Sows are polyestrous, and can produce up to two litters per year. Estrous cycles generally last 21 to 23 days. A sow's gestation period lasts 108 to 120 days. Each litter consists of 5 to 6 piglets on average. Newborn piglets weigh 0.4 to 0.8 kg and are weaned at 8 to 12 weeks. They continue to grow until age 5 to 6. Interestingly, males have more testosterone in their bloodstream during the winter months and shorter days equate to higher concentrations of sex hormones in the boar's semen plasma. (Chapman and Trani, 2007; Goulding, 2013; Henry, 1968; Kozdrowski and Dubiel, 2004; Webster, et al., 1985; Wood and Barrett, 1979)
Males do not give any parental care as they are polygynous and usually travel alone. Female parental care is likely lower in this species than in sheep, cattle, and goats, which could be a trade-off for larger litter sizes. While these comparable species generally only have 1 or 2 young per litter, wild boar litters are 2 to 3 times this size. Not surprisingly, piglets have a high mortality rate. At birth, piglets have very little body fat and few energy stores. By producing more young, female boars increase the chances that some offspring will survive. Sows with large litters have been known to accidentally crush their progeny. However, research suggests that this may be purposeful, to increase the odds of survival for the rest of the litter. Reduced competition among siblings for feeding is a result of smaller litter sizes. Weaker piglets may try to feed several times, before being beaten out by their siblings, and simply dying from malnourishment. Females farrowing piglets close to the same time within a sounder may allow piglets from another litter to nurse. However, more often sows reject piglets that are not their own. Females work collectively to protect all offspring within their sounder. When traveling, mothers keep their young in the middle, with adults in the lead and rear. Young are often left with one female as protection, while the rest of the group forages for food. (Andersen, et al., 2011; Drake, et al., 2008; Graves, 1984)
The maximum known lifespan of a wild boar in their natural habitat is 9 to 10 years. On average, they only live to be 1 to 2 years old. There are few reliable sources regarding their survival rates in the wild. One subspecies, Sus scrofa riukiuanus, reportedly lived 27 years in captivity. Mortality for both male and female boars in the wild is greatly affected by pressures due to hunting. When sport hunting, it is likely that older males will be harvested because they are considered trophy animals. This can skew longevity numbers towards lower lifespans for males, particularly older males. (Braga, et al., 2010; De Magalhães and Costa, 2009; Jezierski, 1977; Toïgo, et al., 2008)
Female wild boars are social animals that tend to live in groups. These groups, called sounders, are generally made up of several females and their offspring. They move their home range as needed, according to resource availability and weather. Males tend to be more solitary after reaching maturity and join with groups during mating. Depending on their habitat, wild boars may be active both day and night. In seasonally warmer weather, they tend to stay fairly inactive during the day. They stay in the shade and wallow in water sources to keep cool. This protects them from insects and helps remove ectoparasites. If boars actively feed during the day, they tend to avoid open areas that would make them more vulnerable to predation. In cooler conditions, these boars may feed during the day, but foraging activities usually increase in the late evening. During the evening and night, wild boars emerge in open areas to search for food. (Boitani, et al., 1994; Graves, 1984; Webster, et al., 1985)
Their home varies with several factors including the number of individuals in the group, food resource availability, geographic range, and predation threats. Females tend to occupy a smaller region and keep to covered areas within a home range to protect themselves and their young. Groups of females accept some overlap between their herd and others, but sounders remain distinct groups. Males are inclined to occupy a larger area. They tolerate overlap of ranges with other males, but during mating season, they become more territorial as they prepare to compete for breeding rights. On average, wild boars have territorial sizes of 1.1 to 3.9 square kilometers. (Boitani, et al., 1994; Graves, 1984)
Wild boars communicate vocally, using growls to indicate aggressive behavior and squeals to show excitement and approachability. Their long, flattened snouts allow for a heightened sense of smell. As pigs forage for food, they tend to keep their snout near the ground. This can impede their ability to smell, making it harder to smell possible danger. They also use chemicals to interact with each other. By rubbing on the ground, they can leave chemical traces behind. Their eyes are located on the sides of their head, giving them good peripheral vision. They mostly rely on their well-developed sense of smell and hearing. There has been very little research on sow-piglet recognition, but in the domesticated subspecies, Sus scrofa domesticus, studies show that sows use their incredible sense of smell to distinguish their own piglets verses piglets from other litters just 24 hours post-partum. (Graves, 1984; Maletínská, et al., 2002; Morton, 1983)
Wild boars are omnivorous. They predominantly eat plant matter, particularly crops, fruits, nuts (mast), roots, and green plants. They have also been known to consume bird eggs, carrion, small rodents, insects, and worms. Wild boars have reportedly preyed on small calves, lambs, and other livestock when the opportunity presents itself. They adjust their diets based on what is available, which can vary with seasons, weather conditions, and locations. They tend to do most of their foraging in the late evening and into the night. (Chapman and Trani, 2007; Graves, 1984; Schley and Roper, 2003; Webster, et al., 1985)
Humans are the main predator of wild boars. Wild boars can be destructive to farmland and natural ecosystems causing humans to implement removal procedures. Young wild boars are targeted by predatory animals such as coyotes and bobcats, while juveniles and adults may fall prey to larger predators such as American black bears and cougars. Adults use their coloration to help them blend in with their surroundings. Piglets have stripes running the length of their back, enabling them to remain concealed within undergrowth and in their nest. By traveling in sounders, sows are able to collectively protect their young from predation while on the move. When traveling, sows lead and pull up the rear while the piglets are kept in the middle of the herd. (Chapman and Trani, 2007; Fang, et al., 2009; Graves, 1984; Webster, et al., 1985)
Wild boars often have a negative effect on the ecosystems, especially if they are an introduced species. They can be very destructive to the habitats of other animals in the area. When nesting in preparation to give birth, females use saplings and other woody plants that they either break off or uproot completely, impacting the ability of new trees to grow. When grubbing for food, they may displace soil and small undergrowth, encouraging erosion and soil deterioration. Studies have shown that seed survival and success, as well as species richness for many plants decreases in plots of land that wild boars can access. Wild boars host a variety of parasites including Trichinella species, Toxoplasma gondii, Gongylonema species, lungworms, kidney worms, stomach worms, ascarids, whipworms, American dog ticks, and hog lice. Many of these are transmissible to humans and other animals. While the parasites may directly lead to death, in most instances they cause the animal's health to deteriorate and they succumb to various environmental elements. Wild boars and their young provide a food source for various animals including bobcats, coyotes, and cougars, among others. (Chapman and Trani, 2007; Henry and Conley, 1970; Ickes, 2001; Ickes, et al., 2005; Meng, et al., 2009)
An important economic pastime that has risen in popularity is recreational fee-hunting for various wild animals, including wild boars. It is very beneficial to both wildlife and landowners. There are monetary incentives for the proprietors, which allows them to take better care of their property. This in turn gives the various animals that may be kept there a good habitat. At the same time, this helps keep down the population of wildlife like wild boars who can be destructive when present in large numbers, and allows for some control on how many animals are being harvested. Hunting on wildlife reservations also increases the likelihood that safe hunting practices will be implemented. Wild boars are one of the most popular wild animals hunted for both sport and food. They are hard to get rid of once a population establishes itself, and so numbers may dwindle, but generally the herds bounce back. Domestic pigs are also desirable as a food source for humans, as well as a source of income for farmers. They become sexually mature at a young age and may reproduce up to twice a year, producing large amounts of offspring, quickly increasing populations for either hunting or harvesting for consumption. (Butler, et al., 2005; Graves, 1984; Oliver and Leus, 2008)
Wild boars can be very problematic for farmers. Crops are often susceptible to damage where wild boars are prevalent. While foraging for food and seeking shelter, they often trample through farm fields. In addition, wild boars have the potential to harbor several diseases and parasites that may be transmissible to domestic livestock and humans. Livestock often contract diseases from being in close proximity with wild boars. Humans may come into contact with infection by either ingesting the meat of a domestic animal that came into contact with an infected wild boar, or eating the meat of a sick wild boar. The damage caused by wild boars can be very costly, especially to farmers. In addition to losing money on their damaged crops and either loosing or having to treat their infected livestock, they may have to build better barriers to keep the wild boars out. Damage caused by introduced wild boars can be so detrimental to some environments that it may lead to endangerment and extinction of native flora and fauna. In particular, the Galapagos Archipelago has had major repercussions since their introduction shortly after Darwin's visit to the islands. Because of their omnivorous foraging tendencies, these pigs have wreaked havoc on many of the islands indigenous plants and animals alike. Eradication measures have been implemented since the late-1960s and have proved successful in purging the foreign species from Santiago Island in particular, the largest introduced pig removal. Close to 19,000 wild pigs were eliminated from the island. (Cruz, et al., 2005; Geisser and Reyer, 2004)
Most wild boar populations are in no danger of becoming endangered or extinct. In fact, there are many programs in place to help control and reduce their populations around the world. They have become a nuisance in places where they were introduced and prove to be difficult to regulate once they are established. Studies have shown that hunting is the most effective way to stabilize their numbers. Other options include installation of fencing, trapping, and strategically placed feeders to lure the boars away from inhabiting undesired areas. There are limits in place for hunting such as seasons and bag limits to ensure they are not over-harvested. There are also specific hunting methods that may be implicated depending on what end result is desirable. "Espera" hunting is done at night using bait to lure wild boars. This allows for a more precise harvest because it gives the hunter more time. If the purpose of hunting is to rid or thin out populations, this helps hunter determine the gender and age of the boar. Due to religious restrictions on the consumption of pork, some countries observe an increase in their local wild boar populations. One subspecies, Sus scrofa riukiuanus, was placed under the 'vulnerable' status in 1982. Widespread development of the Ryukyu Islands has threatened many endemic species, including this subspecies. They are thought to be endangered on several of the islands, although they have not been officially listed. A national park has been established, but increasing expansions looming on the horizon plan to use some of the land for roadways that will limit their habitat and give easier access to poachers who have already wiped out over half of the preserved wild boar population. (Braga, et al., 2010; Chapman and Trani, 2007; Geisser and Reyer, 2004; Oliver and Leus, 2008; Webster, et al., 1985)
Kristin Wickline (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
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.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
uses sound to communicate
living in landscapes dominated by human agriculture.
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.
flesh of dead animals.
either directly causes, or indirectly transmits, a disease to a domestic animal
uses smells or other chemicals to communicate
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.
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
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.
parental care is carried out by females
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
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).
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
found in the oriental region of the world. In other words, India and southeast Asia.
having more than one female as a mate at one time
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
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).
Living on the ground.
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.
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.
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.
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
young are relatively well-developed when born
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