Wild pigs (Sus scrofa) were first observed at Pinnacles National Park in the late 1960s, but the story began a century earlier. In 1769, Spanish explorers introduced domestic swine to California as a food source and to clear land. Allowed to roam freely, these domesticated pigs inhabited various parts of California as feral or wild hogs. The European wild boar was imported to Monterey County in 1925 for hunting purposes, and has successfully interbred with feral hogs already established. These hybrids have spread throughout much of California, both naturally and with the aid of hunters and landowners. The wild pigs that have invaded Pinnacles are a combination of European wild boars, feral hogs, and hybrids of the boar and hog. Wild pigs are not native to California. They are considered exotic species.
Wild pigs consume an abundance of plant matter including acorns, grasses, forbs, berries, roots, and bulbs. They also feed on ground dwelling insects, worms, reptiles, amphibians, fish, small mammals, and carrion including other pigs. Wild pigs spend much of their time rooting or digging with their noses in search of these food items.
Pigs tend to prefer cooler more shaded areas, do not tolerate heat well, and must have a constant water supply in order to survive. They are primarily nocturnal in the hotter months and prefer oak woodlands along streams and chaparral habitat. Here they forage for food, wallow in mud and water, and seek shelter from the sun.
Wild pigs have a high reproductive rate. If there is a sufficient supply of food to accommodate a sow, she can have two litters a year. Litters range from 4-14 piglets. Pigs can adapt to harsh environments and have few natural predators, making them difficult to control.
Wild Pig Impacts
Because wild pigs are not native to Pinnacles National Park, their behavior alters the natural processes that occur in the park. This behavior has been shown to have a negative impact on the plants, animals, and soil.
Rooting by pigs disturbs natural plant communities by destroying native species. The soil is uplifted by this rooting behavior, causing it to dry in the heat of summer. Plants have to work harder to find water and their chances for survival are decreased. Areas that once had native plants become susceptible to the establishment of exotic plants. These exotic species compete with native plants for available space, ultimately compromising the natural order of the plant community. Pigs also consume large amounts of fruits, nuts, and seeds, which decreases the ability of new plants to germinate.
Pigs compete with deer and other wildlife for acorns, insects, and other food sources. Pigs also prey on a number of animals and insects, directly threatening their survival. Besides competing with and preying upon animals, wild pigs have the potential to infect animals, as well as humans with a number of diseases and parasites. Rooting behavior also adversely affects the habitat of ground dwelling animals such as amphibians, reptiles, mammals, and ground nesting birds.
Pig rooting significantly increases the rate of erosion. Pigs root near stream banks causing the soil to loosen and wash away during rains. When soils wash into streams and creeks the water quality is decreased. Poor water quality has a negative impact on many aquatic animals including the threatened California red-legged frog.
Management of Wild Pigs
The National Park Service has a policy of conserving, protecting, and restoring native plants and animals. Park managers at Pinnacles National Park are required to control or eradicate non-native species that have a negative impact on its resources. In 1984, the Park staff had considerable concerns about the increasing number of wild pigs and the destruction they were causing to the Park. After several years of research and testing, the Park decided to construct a fence around the perimeter that would prevent pigs from invading the park.
The fence is designed to prevent pigs from rooting underneath, while allowing animals of various sizes to pass through, or jump over. Completed in 2003, the fence surrounds more than 14,000 acres of parkland and stretches a distance of roughly 24 miles.
Upon completion of the pig-proof fence, the Park contracted wildlife biologists from the Institute for Wildlife Studies (IWS) to eradicate exotic pigs within the fence-enclosure. Using ground-hunting methods, trained dogs, and traps, and subsequently monitoring for pig sign, IWS staff deemed the fence-enclosed area of the Park free of pigs in June 2006.
In 2010 the park added another nine miles of fence to protect more than 2,000 additional acres of sensitive habitat, including wetlands and riparian areas where federally Threatened California red-legged frogs breed.
Park staff will continue to regularly patrol the fence to ensure that pigs cannot penetrate the barrier. If pigs do enter the fenced area of the Park, measures will be taken to eliminate pigs from within. Now that exotic pigs have been eliminated from the core area of the Park, routine monitoring and maintenance measures are crucial to maintaining a pig-free environment.
One of the goals of Pinnacles National Park is to maintain this pig-free environment in perpetuity within the fenced portion of the Park. The unique and wondrous diversity of flora and fauna that has evolved here depends upon this.