August 2005 Wild hogs in the woods Wildlife and agriculture officials take a stand in the mud to ferret out feral pigs from pockets of the Wisconsin countryside. Kyle LaFond

Feral pigs have gained a foothold in 23 states, including 15-16 pockets in 25 Wisconsin counties, mostly in Crawford and LaCrosse. © Russell L. Stevens
The Samuel Roberts Noble Foundation, Inc.

In the past four years, conservation wardens and wildlife biologists in western and northeastern Wisconsin have spent considerable time responding to periodic reports of wild pigs. Unfortunately these animals are not well-bred, barnyard variety porkers, but they are very intelligent animals. Their discovery threatens farmlands, farm herds and sensitive wild habitat.

Though now well established here, feral pigs are not native to the United States. They are descendants of animals that came ashore with colonists and conquerors. Pigs were first introduced into southern coastal areas by Spanish explorers during New World exploration/exploitation. The population and distribution of feral pigs has increased to 23 states and they especially cause problems in southern states where milder temperatures encourage larger herds that grow more quickly. Feral pigs today are most plentiful in the coastal states along the Gulf of Mexico, California and along the Eastern Seaboard north through the Virginias. Many are descendants and hybrids of Russian wild boars originally introduced for hunting. Through each successive generation, domestic characteristics have diminished and the animals have developed traits necessary to survive in wild environments.

Feral pigs are usually smaller, leaner and more muscular than domestic swine. They possess larger and more elongated snouts, longer and coarser hair, straight tails with sparse hair, and big tusks. (The upper ones are often 3-5 inches long and are canine teeth that grow continuously. They are used for defense and for establishing breeding dominance). Their cloven hooves and tracks look a bit like deer tracks. These wild pigs are also mean and fast. The pigs normally trot between feeding areas and then slow to a walk. They can run for short spurts at speeds up to 30 miles an hour and are good swimmers. Feral pigs have poor eyesight, but excellent senses of hearing and smell that they have honed in adopting nocturnal lifestyles. Coloration is highly variable, and most young and juvenile animals are black. Some are lighter in color and have moderate striping that help conceal them.

Feral pigs are extremely adaptable and highly reproductive. Under optimal conditions, female pigs may breed as early as six months of age. Sows typically produce two to four litters per year of four to 10 piglets per litter. Food and nutrient shortages can delay breeding and reduce the number of piglets, but feral pig populations rebound quickly when conditions improve.

Feral pigs may have a lifespan of six to 10 years where conditions allow. Most die from starvation, parasites, disease, accidental death, predation and hunting.

Feral pigs rely upon several types of habitats -- daylight nesting areas where they rest and wallow to minimize the influence of foul weather. These sites commonly consist of dense vegetation near a natural source of water. Second, feral pigs use more open and exposed feeding and watering areas at night, typically agricultural fields, wetlands and woodland openings. Both nesting and feeding sites are messy mixes of wide trails with lots of tracks, scat and wallows. Wild pigs scratch the ground to dig out wallows to create muddy areas where they can escape the heat and roll in mud to fend off biting insects.

Wildlife biologists look for signs of wild pigs from the air. Where feral pigs are abundant, they move at dawn and dusk between nesting and feeding areas. That’s when they are most often seen by hunters.

Feral pigs are social animals that travel in groups called sounders. A sounder typically consists of one or more sows and their offspring. Weaned piglets remain with their mother until another litter is due or until they reach sexual maturity and begin mating. Adult boars (usually older than 18 months) are almost always solitary animals that consort with sounders only to mate or nose their way into productive feeding areas.

Food abundance and availablility dictate their range. In times of plenty, the ranges are pretty small. Winter ranges expand as food and protective shelter become scarce. Spring and summer ranges are usually much more concentrated near recently planted, growing crops.

The United States Department of Agriculture (USDA) estimates crop damage by feral pigs costs the U.S. farm economy about $800 million annually. © Phil Peterson, USDA Wildlife Services

Feral pigs are opportunistic omnivores that eat, well…like pigs, consuming a wide variety of plants and animals. Where wild pig populations build up, they damage crops during the spring planting season, rooting for tender roots, shoots, bulbs, tubers and the nutritious early growth. Berries, fruits, roots, tubers, agricultural crops, crayfish, salamanders, snakes, eggs, ground-nesting birds fawns and young livestock are all eaten. Fall is also a feasting time when acorns, nuts and other mast are plentiful. Feral pigs also scavenge on any animal matter that they may happen across including the remains of dead animals, weak or sickened animals, and newborns of both wild animals or domesticated livestock.

Barstool biologists speculate how feral pigs arrived in Wisconsin. Three theories seem most plausible. The first suggests feral pigs escaped or were intentionally released from game farms. The second holds that feral pigs had been released by recreational hunters for sporting and training purposes. The third and most popular assumption is that bear hunters released feral pigs to train their dogs to pursue bears. Since wild pig populations are so spotty and seem to build up in small pockets with huge areas between them, human intervention in establishing these populations seems like a more likely explanation.

Biologists from other states also note a correlation between feral pig populations and trophy whitetail deer populations. That’s led some to speculate the pigs may have been stocked by poachers who want to illegally harvest trophy deer out of season under the guise that they are hunting feral pigs. In many states including Wisconsin, feral pigs are regarded as a nuisance species that may be hunted throughout the year using the same firearms as one would use for deer hunting.

The discovery of feral pigs in several locales throughout Wisconsin raises concerns for crop damage in the immediate area and more widespread threats to animal health and agribusiness.

Biologists throughout southern states have documented damage and real destruction that feral pigs bring to the landscape. They compete for food with deer, grassland birds like quail and upland birds like turkeys. Most alarming, the wild pigs can root and decimate sensitive landscapes that contain or support threatened or endangered species. Pigs can also spread invasive species by rooting vegetation and disturbing ground cover. In wetland habitats pigs have destroyed areas essential to migratory game birds, songbirds, amphibians, reptiles and small mammals. Feral pig activity may also cause erosion and in the process, lower water quality, harming spawning areas for fish species.

Beyond the threats to natural habitats, the United States Department of Agriculture (USDA) estimates crop damage by feral pigs costs the U.S. farm economy about $800 million annually. Damage to croplands in the spring and summer during planting and early growth is especially acute.

Crop damage is small compared to the threat feral pigs pose as a vector for spreading communicable diseases. Feral pigs carry several diseases that can spead to domestic livestock, wildlife species and humans. Swine brucellosis and pseudorabies outbreaks would be especially devastating to commercial pork producers. The industry has invested heavily in testing and disease-control programs to prevent outbreaks of both diseases. The chance that wild pigs could harbor these diseases and subsequently infect a domestic herd is a huge concern to commercial producers. Swine brucellosis causes abortions in sows and infertility in boars. This disease is non-fatal, but it spreads readily and can severely reduce reproduction and profits on swine farms. Infected animals are disease carriers for the remainder of their lives as there is no effective treatment. Removing and sacrificing infected pigs is the only effective means of containing swine brucellosis outbreaks. Further, the disease has affected cattle and humans in very rare circumstances.

Pseudorabies is caused by a herpes virus and is not related to rabies. The virus compromises an infected animal’s immune system leaving it susceptible to other diseases. Infection also causes abortions and stillbirths. Carriers are infected for life and must be removed from the population. Pseudorabies infection can have serious consequences if transmitted to domestic livestock, but can’t spread to people. Cattle, sheep, goats, dogs, cats and rodents are all susceptible to this disease and may die following infection.

If feral pigs become infected, they could become a reservoir of serious disease threats like tuberculosis, trichinosis, anthrax, foot and mouth disease and classic swine fever that we are trying to keep out of the state and the country.

Feral pigs are destructive, non-native, wild animals. The Wisconsin Department of Natural Resources supports the aggressive removal of feral pigs wherever they occur since established populations may have many adverse, long-term consequences. Though pockets of feral pigs have been sporadically reported in Wisconsin, the only known self-sustaining population is a group of about 130 animals living in a 50 square mile region of Crawford County.

Please act responsibly and don’t stock or introduce feral pigs into the state. If you are aware of anyone stocking or introducing feral pigs, please contact and alert your local conservation warden.

Feral pigs are currently classified as an unprotected species in Wisconsin, which allows hunters to pursue them throughout the year without any season or bag limit restrictions. To harvest a feral pig, the hunter only needs a small game license, or its equivalent, and the permission of a landowner if hunting on private property.

When pursuing feral pigs, take these precautions to minimize health risks. After harvesting a feral pig, contact the local conservation warden or wildlife biologist. These professionals will document your harvest and withdraw blood samples to test the animal for disease. If you choose to keep the animal for personal consumption, wear protective disposable rubber gloves when field dressing and cleaning the animal. Avoid direct contact with blood and reproductive organs. Bury the offal. Clean and disinfect all equipment after use. Cook the meat thoroughly.

Kyle LaFond formerly served as a DNR wildlife biologist and the assistant bear and elk ecologist.

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