Wild Pigs

Preserving Ecosystems: Wild Pig Control at Pinnacles

History of Wild Pigs at Pinnacles

Wild pigs (Sus scrofa) were first observed at Pinnacles National Park in the late 1960s, but their story in California began much earlier. In 1769, Spanish explorers introduced domestic swine to the region as a food source and to clear land. These pigs roamed freely, becoming feral in various areas of California. In 1925, European wild boars were brought to Monterey County for hunting, and they interbred with the existing feral pigs. These hybrids spread naturally and with the help of hunters and landowners, eventually invading Pinnacles. The wild pigs at Pinnacles are a mix of European wild boars, feral hogs, and their hybrids, making them an exotic species in the region.

Wild Pig Ecology and Behavior

Wild pigs consume a wide variety of plant matter, including acorns, grasses, forbs, berries, roots, and bulbs. They also feed on insects, worms, reptiles, amphibians, fish, small mammals, and carrion. Using their snouts to root and dig, pigs spend much of their time searching for these food items.

Pigs prefer cooler, shaded areas and cannot tolerate heat well, requiring a constant water supply to survive. During hotter months, they are primarily nocturnal and favor oak woodlands near streams and chaparral habitats for foraging, wallowing, and seeking shelter.

With a high reproductive rate, wild pigs can produce two litters per year, ranging from 4 to 14 piglets per litter if food is abundant. Their adaptability, combined with few natural predators, makes them difficult to control.

Impacts of Wild Pigs

Wild pigs, being non-native to Pinnacles National Park, disrupt natural processes and have significant negative impacts on the park’s plants, animals, and soil.

1. Plants

Pigs uproot native plants while rooting, which disrupts plant communities by drying the soil, making it harder for plants to access water and survive. This disturbance creates opportunities for exotic plant species to establish and outcompete native vegetation, altering the natural balance of the ecosystem. Additionally, pigs consume large quantities of fruits, nuts, and seeds, reducing the ability of native plants to reproduce.

2. Wildlife

Wild pigs compete with native wildlife, such as deer, for food sources like acorns and insects. They also prey on smaller animals and insects, directly threatening these species. Furthermore, pigs can carry diseases and parasites that pose risks to both wildlife and humans. The rooting behavior of pigs disrupts habitats crucial for ground-dwelling animals, including amphibians, reptiles, mammals, and ground-nesting birds.

3. Soil Erosion

Pig rooting activities significantly accelerate soil erosion, especially near stream banks, where loose soil washes away during rains. This sediment runoff decreases water quality, harming aquatic species such as the threatened California red-legged frog.

Management of Wild Pigs at Pinnacles

The National Park Service’s policy emphasizes conserving native species and ecosystems. Park managers at Pinnacles are tasked with controlling or eradicating non-native species like wild pigs that negatively impact park resources. In 1984, the increasing number of wild pigs prompted the park to take action. After several years of research, the decision was made to construct a fence around the park’s perimeter to prevent further pig invasions.

The fence, completed in 2003, encloses over 14,000 acres and stretches approximately 24 miles. It is designed to prevent pigs from rooting underneath while allowing other wildlife to pass through or jump over. Wildlife biologists from the Institute for Wildlife Studies (IWS) were contracted to eliminate exotic pigs within the enclosed area using ground-hunting methods, trained dogs, and traps. By June 2006, the park’s fenced area was declared pig-free.

In 2010, an additional nine miles of fencing was installed, protecting over 2,000 more acres of sensitive habitats, including wetlands and riparian areas where the federally threatened California red-legged frogs breed.

Park staff continues to patrol and maintain the fence to ensure pigs do not breach it. Should any pigs enter the fenced area, the park has measures in place for their removal.

Maintaining a pig-free environment is a long-term goal for Pinnacles National Park, ensuring that its diverse flora and fauna can thrive without the threats posed by this invasive species.

http://sfnps.org/feral_pigs