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; their size differences become more obvious as they age. Adult wild boars have a thick, coarse coat of hair. Their coat ranges from black to brownish-red to white. Depending on where they live, they can have a speckled or solid color. They may also have longer bristly hairs that grow down the middle of their backs. At birth, young boars have yellowish-brown stripes down their backs that disappear by 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 are 5 to 10 cm long and are usually 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 (Sus scrofa) are found almost worldwide. They originated in Europe and Asia, but were introduced to North America and are considered an invasive species in the southeastern United States and California. They are common throughout Eurasia, and are found on every continent except Antarctica. (Chapman and Trani, 2007; Oliver and Leus, 2008; Wood and Barrett, 1979)
Wild boars can be found in a variety of habitats. They may inhabit grassy savanna areas, wooded forests, agricultural areas, shrublands and marshy swamplands. Their main habitat needs include nearby water sources and shelter to hide from predators. They are found in many climates, but usually avoid extreme heat or cold. In places with harsh winter temperatures and heavy snowfall, food may be more difficult to find. Deeper snows and frozen ground make it difficult to forage for roots and leaves. (Chapman and Trani, 2007; Melis, et al., 2006; Oliver and Leus, 2008)
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 sows prepare to give birth, they leave the sounder and return with their young. Even after reaching maturity, female piglets tend to stay in the same groups with their mothers. These herds often overlap, and may split into subpopulations. Males stay with their mothers until they are 1 to 2 years old and then leave the herd. After leaving, they usually only join another sounder during mating season. Wild boars are polygynous, meaning males mate with several females. Males are attracted to groups of females that are ready to breed. They become very aggressive and compete for the opportunity to breed with a sounder. Successful males chase females, 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 can breed at any time of the year. However, mating usually depends on the climate, which impacts the amount of available food. If females cannot find enough food, they will not mate. Females can begin breeding at 10 months of age and males can begin breeding at 5 to 7 months of age. Sows can have up to two litters per year. Their gestation period lasts 108 to 120 days. Litters usually include 5 to 6 piglets. Newborn piglets weigh 0.4 to 0.8 kg and are weaned at 8 to 12 weeks. They continue to grow until they are 5 to 6 years old. (Chapman and Trani, 2007; Goulding, 2013; Henry, 1968; Kozdrowski and Dubiel, 2004; Webster, et al., 1985; Wood and Barrett, 1979)
Since males mate with many females and usually travel alone, they do not give any parental care. Likewise, females likely offer less parental care than sheep, cattle, or goats, probably because of their larger litter sizes. Piglets are born with very little body fat and have a very high death rate. By having larger litters, it is more likely that at least a few young will survive. Females with large litters have been known to crush some of their offspring. However, this may be done on purpose, to increase the odds of survival for the rest of the litter. Weaker piglets may try to feed several times, before being beaten out by their siblings, and simply dying from lack of food. Females that give birth to their piglets close to the same time within a sounder may allow piglets from another litter to nurse. Although more often females reject piglets from other litters. Females work together 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)
In the wild, wild boars have been known to live 9 to 10 years. On average, they only live to be 1 to 2 years old. There are not many good sources on their survival rates in the wild. One subspecies, Sus scrofa riukiuanus, reportedly lived 27 years in captivity. These animals are often hunted for sport, especially older males, which are considered trophy animals. This can make their lifespan difficult to determine, as older males are often removed from the population. (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, usually include several females and their offspring. They move their home range as needed, due to food and weather. Males become more solitary after they mature and join groups during the mating season. Depending on their habitat, wild boars may be active both day and night. In warmer weather, they 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 parasites. If boars feed during the day, they tend to avoid open areas where they could be easily seen by a predator. In cooler weather, these boars may feed during the day, but foraging usually increases in the late evening. During the evening and night, wild boars go to open areas to search for food. (Boitani, et al., 1994; Graves, 1984; Webster, et al., 1985)
For wild boars, their home size varies with the number of boars in the group, the food available, their geographic range, and any predation threats. Females usually have smaller home ranges and stay in covered areas to protect themselves and their young. There is some overlap between groups of females, but sounders remain distinct groups. Males keep larger areas. Male ranges also overlap, but during mating season, they become more territorial as they prepare to compete for females. On average, wild boars have territory sizes of 1.1 to 3.9 square kilometers. (Boitani, et al., 1994; Graves, 1984)
Wild boars growl during aggressive behavior and squeal to show excitement. Their long, flattened snouts give them a very good sense of smell. As pigs forage, they keep their snout near the ground, which may make it more difficult to sense any nearby predators. Likewise, they can leave chemical traces by rubbing on the ground. Their eyes are on the sides of their head, giving them good peripheral vision. They mostly rely on their well-developed sense of smell and hearing. (Graves, 1984; Maletínská, et al., 2002; Morton, 1983)
Wild boars mostly eat plant matter including crops, fruits, nuts, roots, and green plants. They have also been known to consume bird eggs, dead animals, rodents, insects, and worms. When it is available, wild boars have also reportedly preyed on small calves, lambs, and other livestock. Wild boars change their diet depending on what is available, which varies 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 may damage farmlands and natural areas, which has caused humans to try and remove them. Young wild boars are preyed on by 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 on their back, helping them hide in their nest and blend in with the undergrowth. By traveling in sounders, sows protect their young from predators while they are on the move. When traveling, sows keep the piglets in the middle of the herd. (Chapman and Trani, 2007; Fang, et al., 2009; Graves, 1984; Webster, et al., 1985)
Wild boars can be destructive. When nesting, 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, causing erosion. Seeds are less likely to survive and fewer plants are found in areas with wild boars. Wild boars host several parasites including Trichinella species, Toxoplasma gondii, Gongylonema species, lungworms, kidney worms, stomach worms, ascarids, whipworms, American dog ticks, and hog lice. Many of these can be transmitted to humans and other animals. 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)
Wild boars can be very problematic for farmers. Crops can be damaged in areas with many wild boars. While foraging and seeking shelter they often trample through farm fields. In addition, wild boars may transfer diseases and parasites to livestock and humans. The damage caused by wild boars can be very costly, especially to farmers. In addition to losing money on their damaged crops, they may have to build barriers to keep the wild boars out. They may also endanger native species. In particular, after the introduction of wild boars to the Galapagos Archipelago shortly after Darwin's visit, they caused major problems for native species. Since the late 1960s, there have been attempts to remove the wild boars. (Cruz, et al., 2005; Geisser and Reyer, 2004)
Recreational fee-hunting for wild boars can benefit wildlife and landowners. Landowners take care of the area, which gives the various animals that are kept there a good habitat. At the same time, it helps keep the population of wild boars under control. 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. Domestic pigs are also an important 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 many offspring, which quickly increases populations for hunting or farming. (Butler, et al., 2005; Graves, 1984; Oliver and Leus, 2008)
Most wild boar populations are in no danger of becoming endangered or extinct. In fact, there are many programs to help control and reduce their populations. They have become a problem in places where they were introduced. Hunting is the most effective way to control their numbers. Likewise, fences, trapping, and luring boars away from undesired areas are also helpful. There are different types of hunting, for instance, "espera" hunting is done at night using bait to lure wild boars. This helps thin the population by giving hunters more time to determine the gender and age of the boar. Due to religious restrictions on eating pork, some countries have larger wild boar populations. One subspecies, Sus scrofa riukiuanus, was given 'vulnerable' status in 1982. Widespread development of the Ryukyu Islands has threatened many species, including this subspecies. They are likely endangered on several of the islands, although they have not been officially listed. (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.
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