Pig (feral or wild)
Common name: pig (feral or wild)
Scientific name: Sus scrofa
Origin: Europe and Asia
Pigs (feral or wild) are an established pest animal in the state of Victoria.
Read more about the classification of invasive animals in Victoria.
History of spread
Feral pigs are descendants of various domestic pig breeds (Sus scrofa) that have been present in Australia since early European settlement. Initially concentrated near settlement areas, feral pig populations have since spread across 45 per cent of the mainland and occur on several offshore islands. These populations have spread by natural dispersal, accidental escape and deliberate release and they have been able to establish, and in many cases flourish, due to their adaptable behaviour and high reproductive rate.
Distribution in Victoria
Feral pigs occur at a number locations throughout Victoria, though their populations are typically isolated and they occur at relatively low densities. Most established populations can be found along the Murray River, near Mansfield, Kinglake, the Grampians and Lancefield. New populations continue to emerge, with some of the more recent being present in the south-west of Victoria.
Population density in Victoria
Feral pig densities vary with environmental conditions. In good years, where food, water and shelter are plentiful, their numbers can increase rapidly. While in poor conditions, such as drought, their numbers can decline rapidly as breeding occurs less often and mortality of young is high. Densities also depend on the habitat type and its productivity. In eucalypt woodland, forests and grazing land, there may be one feral pig per km2, while in wetlands and floodplains there may be as many as 10 to 20 feral pigs per km2.
Feral pigs are smaller, leaner and more muscular than domestic pigs. Their shoulders and necks are also more developed and they have smaller, shorter hindquarters and their hair is more sparse, longer and coarser. Black is the most common hair colour, though they can also be rusty red or mixed colours, including white, light ginger, brown and white, brown with black spots, brindle and agouti (brown or black with a lighter tip). Piglets are sometimes marked with dark longitudinal stripes that disappear as they grow older. Feral pigs also have longer, larger snouts and tusks, smaller ears, narrower backs straight tails with a bushy tip. Importantly, all pigs have small eyes and poor eyesight, but their senses of smell and hearing are well developed.
Males and females differ in size and weight, with male feral pigs being longer and taller than females and weighing more at comparable ages. The weight of an average adult female feral pig is 50 to 60 kg, while males usually weigh 80 to 100 kg. However, this weight can vary with habitat conditions and exceptional animals have reached up to 260 kg.
Feral pigs are primarily nocturnal and restrict most of their activity to the cooler parts of the day at dawn and dusk. They are also shy animals and will avoid humans, especially if they are regularly hunted/disturbed, making it easy to overlook their presence or drastically underestimate their numbers.
Feral pigs have defined home ranges and regularly make use of trails between areas they use for shelter, food and water. The home range of adult boars can vary between 10 to 50 km2 depending on the habitat/environmental conditions, while an adult sow's home range can be between 10 and 20 km2. Furthermore, lactating sows have restricted ranges of less than 5 km2. When a feral pig population has an adequate food supply in its home range, it is unlikely that individuals will travel more than 5 km outside that area, except when mature crops are on offer.
Feral pigs must have daily access to water and wallowing sites, particularly in hot conditions. They will also use regular trails to travel to water from bedding or feeding areas, along which they often rub on trees or logs, and wallow in mud or dusty depressions. These habits help to reduce infection, while mud and dust helps to regulate their body temperature.
A group of feral pigs is often referred to as a 'mob' or 'sounder', which typically consists of related sows (mother, daughters, sisters, aunts, etc.) and their young. Bachelor mobs form when sexually mature males leave or are chased from their mother's group. At about 18 months, males become more solitary and will rejoin the female groups only for mating purposes.
Mob size varies depending on the season and habitat. In forested areas mobs rarely exceed 12 animals, while in more open country, mobs of up to 40 to 50 pigs may form.
Being omnivorous, feral pigs will feed on almost anything and they will switch food preferences depending on its availability. Succulent green vegetation is their food item of choice, but they will eat fruit, grain and a wide variety of animal material such as frogs, fish, reptiles, birds, small mammals and carrion. Feral pigs will eat underground plant materials such as roots, bulbs, corms and fungi and have also been known to predate on newborn lambs and they may also attack newborn calves. A feral pigs need for high energy or protein-rich food is often the reason for their impact on agriculture as they will destroy crops and depredate newborn lambs. However, this need is also a weakness in their ecology that can be exploited for management purposes.
Shelter is vitally important for feral pigs as it provides them with shade and protection from predators. Feral pigs typically prefer to live in moist environments that can provide a reliable and adequate food and water supply.
In Australia, feral pigs are found in a wide range of habitats including:
- rainforest areas
- monsoon forest
- paperbark swamps
- open floodplains
- marsh areas
- semi-arid floodplains
- dry woodlands
- subalpine grasslands
Because feral pigs need to drink daily in hot weather, they are generally not found in the dry inland areas of Australia.
Feral pigs are prone to predation by:
- wild dogs
- large birds of prey.
Diseases and parasites
Feral pigs can be hosts or vectors of numerous endemic parasites and diseases, some of which can affect animals or people. They are also potential carriers of exotic diseases, with the biggest concerns being foot-and-mouth disease and African swine fever should they ever enter Australia.
Feral pigs do not have a defined breeding season and can breed throughout the year, although breeding success depends on the availability of quality food.
Sexual maturity in sows depends on weight rather than age, similar to domestic pigs. A sow may begin breeding from about six to eight months of age, when her weight exceeds about 25 to 30 kg. Sows have a 21-day oestrus cycle and a gestation period of 112 to 114 days. Average litter sizes vary from 5 to 6 piglets, but up to 10 piglets can be born under good conditions. Boars become sexually mature from about 18 months of age.
Just before giving birth, sows will make a nest using available vegetation. Piglets will normally spend the first one to five days of their life inside the nest, with the sow inside or close by. The nest is usually less than 2 km from available water.
A feral pig litter is weaned after two or three months, at which time mating can occur again. Under favourable conditions, a sow can produce two weaned litters in little over a year, thus feral pigs can multiply at a very fast rate. This breeding capacity allows feral pig populations to quickly recover from natural setbacks (drought) or control programs.
Impact on ecosystems and waterways
Feral pigs are considered an environmental pest due to their selective feeding, trampling and rooting for underground parts of plants and invertebrates. They also compete with native wildlife for food, water and shelter and prey directly on various wildlife species and their eggs. In addition, they are known to prey on earthworms, insects, amphibians, reptiles, ground-nesting birds, small mammals, freshwater crayfish, frogs, turtles and their eggs. Consequently predation, habitat degradation competition and disease transmission by feral pigs has been listed as a key threatening process to threatened species conservation under the Environment Protection & Biodiversity Conservation Act 1999 (EPBC Act).
Feral pig activity also has a dramatic effect on watercourses and swamps. By wallowing and rooting around the waterline, they destroy the riparian vegetation which provides food and nesting sites for native wildlife and helps to prevent soil erosion. Water quality is also affected, and their diggings may spread undesirable plant and animal species, and plant diseases in these areas.
Agricultural and economic impacts
Feral pigs cause significant damage in agricultural areas. They prey on newborn lambs, compete with livestock for pasture and can damage infrastructure such as fencing and water facilities. Feral pigs impact grain, sugarcane, fruit and vegetable crops, through uprooting and consuming or trampling of plants, and their wallowing and defecation fouls dams and waterholes. Feral pigs can also transport weeds and ground rooting provides ideal conditions for weed establishment.
Feral pigs are vectors for a number of serious endemic and exotic diseases that have the potential to devastate commercial pig operations, as well as infect other animals and humans. Examples include:
- foot-and-mouth disease
- Japanese encephalitis
- African swine fever.
Social values and health
Feral pigs can be seen as a food and a valuable hunting resource to some members of the community. However, it is important to remember the damage caused by feral pigs to agriculture and the environment, and their ability to carry and spread of exotic diseases far outweighs any potential benefits.
Recommended control measures include:
- exclusion fencing.
The department recommends integrated pest management using all suitable control tools in a coordinated manner at a landscape scale.
Read more about the management and control of feral pigs.
- Animal Control Technologies 2004, Feral Pig Problems in Australia, Animal Control Technologies, viewed online 16th March 2010
- Choquenot, D, Mxllroy, J and Korn, T 1996, Managing Vertebrate Pests: Feral Pigs, Bureau of Resource Sciences, Australian Government Publishing Service, Canberra.
- Croft, D 2007, Vertebrate Pest Control Manual: Feral pig biology and control. State of New South Wales, NSW Department of Primary Industries.
- Department of the Environment and Heritage 2004, The feral pig (Sus scrofa), fact sheet, viewed 16th March 2010.
- Invasive Animals CRC, The feral pig (Sus scofa), viewed 16th March 2010.
- Land Protection (Invasive plants and animals) 2008, Feral pigs in Queensland – distribution, ecology and impact, fact sheet, The State of Queensland, Department of Primary Industries and Fisheries.
- McGaw, C.C and Mitchell, J 1998, Pest Status Review Series: Feral Pigs (Sus scrofa) in Queensland, Department of Natural Resources and Mines, QLD
- Mitchell, J 2008, Feral Pig Control – A practical guide to pig control in Queensland, The State of Queensland Department of Primary Industries and Fisheries.
- Queensland Government Department of Natural Resources and Mines 2005, A guide to pest animal management in Queensland – Vertebrate pest manual, The State Government of Queensland, Queensland, Australia.
- Regan, K 2002, Landcare Notes: Feral pigs in Victoria, LC0306, Department of Primary Industries, State Government of Victoria.
- West, P 2008, Assessing Invasive Animals in Australia 2008. National Land & Water Resources Audit and Invasive Animals CRC, Canberra
Figures 1–5 courtesy of Jason Wishart