Feral pig FAQs
The following are some frequently asked questions about pest animals. You may be able to find more information about some of these questions from the relevant species page or by searching the database on this site.
Frequently Asked Questions about feral pigs
Q. Are they from one source?
A. Most feral pigs in Australia are descended from various breeds of the domestic pig Sus scrofa. The main contributors were probably the European Berkshire and Tamworth which had already been heavily modified by cross-breeding with other breeds from China, India, Italy and Portugal. It is also believed that some populations in the Northern Territory and Queensland may have originated from Sus celebensis, a separate species imported from Timor. These animals are thought to have later interbred with pigs of domestic origin.
Q. How big are they?
A. The weight of feral pigs depends on the quality of the habitat but generally adult males range up to 115 kilograms and sows 75 kilograms. In some cooler and wetter areas feral pigs can grow very large with a 175 kilogram boar caught just south of Canberra while boars over 200 kilograms are regularly caught in New Zealand.
Q. Do they revert to the wild boar type?
A. Feral pigs originate from escaped or released domestic pigs that have adapted to survive and breed in the wild. After several generations in the wild they tend to become more like their wild boar ancestors being taller, leaner and more muscular than their domestic relatives with well developed necks and shoulders and smaller and shorter hind quarters. They also have larger and longer snouts and develop tusks. Some individuals develop a crest or mane of longer bristles from their neck to the middle of their back. These can be erected when the animal is enraged leading to the name razorback.
The colour size and shape of feral pigs varies considerably across Australia and probably reflects the characteristics inherited from the domestic breeds which originally escaped or were released.
Q. When do they breed and how many young do they have?
A. Feral pigs will breed continuously if there is sufficient, high quality food but generally they are seasonal breeders due to the variable availability of food. For example, in the NSW highlands, young are mainly born in summer and autumn in response to the early flush of growth that follows winter whereas they breed all year on the flood plains of western NSW. There are however, more births in western NSW following the flush of food associated with good rains.
The pregnancy period is about 16 weeks with the average litter being five to six, with 10 possible under very good conditions. Sows breed at about 25 to 30 kilograms which they reach at about seven to 12 months. When there is a continuous supply of quality food, sows can produce two litters in 12 to 15 months although one litter a year is more common. Nearly all adult females breed.
A feral pig population has a potential rate of increase of 86% a year. This high potential reproductive rate is closer to that of rabbits than other large herbivores such as feral goats and enables feral pigs to rapidly recover their numbers from setbacks due to drought or control. This is an important factor to be considered when planning control programs.
Q. How far do they move?
A. Individuals can move up to 55 kilometres for example, to go from one watercourse to another in search of food or in response to major prolonged disturbance due to control programs. However, most feral pigs retain a strong attachment to their home range, even when subject to minor disturbances such as low level hunting. Intensive hunting is different and may cause feral pigs to leave their home area.
Feral pigs like to use familiar trails to move from one part of their territory to another; for example from sites they use to shelter from the heat to water or feeding grounds. Other regularly visited sites are dust or mud wallows which pigs use to help remove external parasites and/or to cool themselves. Identification of feral pig trails and other regularly visited sites can greatly help plan and implement an effective control program.
The home range of feral pigs varies according to the distribution and quality of food and water and the density of the population. Generally boars have a larger home range than sows. The home range of boars in western NSW is about 10 square kilometres while it is only six for sows. The size of the home range is similar in the sub-alpine areas of NSW while in north-western NSW, the range is 10 square kilometres for boars and between 5 and 8 for sows. Daily movements are much smaller than the total home range, with only one to 1.5 square kilometres covered in a day. The daily home range is much smaller for farrowing sows at about 2.0 square kilometres.
Q. What is the social structure of feral pigs?
A. Feral pigs are social animals and form a variety of groups. The most common is one or more sows and their piglets but groups may also consist of young sows, bachelor males and other combinations. Bachelor males generally stay together until they are about 18 months old after which they tend to be solitary and only join groups for mating or to feed on localised sources of food.
The size of feral pig groups varies considerably across Australia. In the open country of western NSW, the group size is usually about 10 but may increase to 50 or more especially if the range of the animals is restricted to remaining water points due to drought. In the cooler forests, group size rarely exceeds 12 animals.
Q. What do they eat?
A. Feral pigs have a similar digestive system to humans. They are opportunistic omnivores with a strong preference for succulent green vegetation, a wide variety of animal material, fruits and grain. Other foods include underground, starch-rich plant material such as roots and bulbs. They will also take fungi, earthworms, snails, eggs of ground nesting birds, turtle eggs, lambs and carrion. Like domestic pigs, feral pigs need a diet high in protein (more than 15%) in order to breed and feed their young.
Both the availability and nutritional level of food available for feral pigs changes considerably with the season. For example, in western NSW, feral pigs feed mainly on green vegetation after rain. During dry periods they eat roots, carrion and little else.
Q. Do they need water and cover?
A. The distribution of feral pigs in Australia is mainly restricted by the availability of adequate water. They can withstand high temperatures but only where there are adequate supplies of water and shelter from the heat of the day. They tend to avoid the extremes of the day by being active at night and in the early morning and evening. Water is less important in the cooler forests where they can be active for much longer during the day.
Q. What are the main causes of mortality?
A. Mortality of young piglets is generally high and is mainly due to starvation and separation from their mothers. Virtually all piglets in an area will die when conditions are poor such as during droughts. This falls to a loss rate of about 10 to 15% when there are good supplies of food and weather conditions are favourable. Adult mortality varies from 15% to 50% and is caused mainly by starvation and human intervention. Few adults live past five years of age in western NSW. Dingoes and feral dogs can also take substantial numbers of young pigs but it is not known whether dogs can limit the size or the distribution of feral pig populations.
Q. How many are there in Australia?
A. Feral pigs occupy about 38% of mainland Australia and number anywhere between 3.5 million and 23.5 million. The wide variation is because it is very difficult to accurately estimate of the total number as their distribution and abundance can vary greatly due to changing environmental conditions from year to year. Their numbers drop dramatically during drought but can increase greatly in a run of good seasons. Feral pig densities in different habitats vary from about one pig per square kilometre in drier woodland and grazing land to 10 to 20 per square kilometre in wetlands and floodplains that are seasonally flooded.
Q. What diseases do they carry?
A. Feral pigs carry many diseases that can affect the health of domestic livestock, native animals and humans. These include leptospirosis, brucellosis, sparganosis, melioidosis and Murray Valley Encephalitis. Pigs can also carry some economically important exotic diseases such as Foot-And-Mouth disease (FMD) and swine fever.
FMD is probably the disease most feared in Australia by primary producers, food processors and government authorities. An outbreak of FMD in Australia could immediately close down some 90% of our export market for animal products, and cost Australia up to $3 billion in lost export trade, even if the disease was eradicated immediately. If the outbreak persisted, continuing losses could be between $0.3 billion and $4 billion a year, depending on whether the trade was affected in just one state or country-wide. Feral pigs are considered to be the main potential wild host for FMD and it has been estimated that the disease could cover 10 000 to 30 000 square kilometres before it could be first detected. In some ways it is fortunate that in most parts of Australia, feral pigs are in relatively close contact with livestock, which might aid early detection of an outbreak of FMD. The difficulty in detecting exotic diseases in wild animals such as feral pigs also has trade implications. It would be hard to demonstrate to Australia’s trading partners that all feral pigs in the area where the disease broke out are free from FMD.
To reduce feral pig density to a level where the disease could no longer survive would be difficult if not impossible. For some pig populations this may require a reduction of 95% of the population, yet in three full-scale trial programs in New South Wales, Northern Territory and Queensland only a 40 to 80% reduction was achieved. In most cases, the most practical approach to an outbreak of FMD would be to focus on managing the outbreak in domestic herds and to contain it, rather than to attempt to eradicate it in wild animal carriers.