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Spring 2000

Pigs, Pigs and More Pigs...
Feral Pigs Invade the Santa Cruz Mountains

by Emily Johnson and Geoffrey Skinner

Don't be surprised if on your next hike through Bay Area trails, one of these long-snouted, grunting animals approaches you.

Feral pig in Sunol Regional Wilderness -- click for larger image [127Kb]
Feral pig in Sunol Regional Wilderness -- click for larger image [127Kb]
Photo by Terry Smith. Reprinted by permission.
The wild pig population of the Bay Area is growing rapidly, and is becoming increasingly more aggressive with its surroundings. This pig invasion is leading certain counties to take action on damage control, and to discuss how to share the land with the beasts.
      Domestic pigs (Sus scrofa) first arrived in California with the Spanish in 1769. Over the next century, European settlers continued to bring pigs into California. In 1925, Eurasian wild boar stock from North Carolina was introduced for hunting near Carmel and soon began migrating beyond the Monterey area, interbreeding with existing feral pig populations. Although no accurate pig count has ever been made, estimates put the total California feral pig population as high as 80,000.
      Most of the pigs in the western Bay Area originated in the Monterey area and are rapidly increasing their range particularly the southern portion. With no real predators in the area for these animals, their numbers are booming as they reproduce at a prodigious rate. Feeding off of fallen acorns and digging around trees, the pigs pose a threat to the future generations of oak trees and the surrounding root structure of the current trees. They also endanger farming land, and could be a potential disease factor. In addition, they may be competing with other wildlife for food, and may be one reason for a decreasing deer population. While pigs have been a notable presence in the Diablo Range for many years, they have only more recently made themselves known in the Santa Cruz Mountains.
      As the pig inhabitants become more possessive of the land, small deer and even humans can become targets for their aggression. Creating a fence barrier and hunting are two methods used by Mount Tamalpais State Park to control its pig population. The Midpeninsula Regional Open Space District is also evaluating methods for controlling the pigs on public as well as private properties in the South Skyline area. In the San Mateo County, pigs are being monitored at Pescadero and Sam McDonald County Parks. Santa Clara County Parks & Recreation has had luck by focusing on recreation areas, especially campgrounds, and has since been able to decrease the level of interaction between the pigs and humans. Santa Clara County has actively controlled pigs through trapping, particularly in Mount Madonna County Park.

The Pig Control Program at Long Ridge

Jodi Isaacs, biologist with MROSD, said that MROSD is moving toward a pig control program. $20,000 has been budgeted; the full Board hasn't yet voted on the matter, but she expects it to be approved because it gained unanimous approval in Board committee. Once approved, the District will hire a contractor to trap and remove pigs in the Long Ridge area for the next three years. They will evaluate the test program each year by measuring pig activity - has it decreased, remained the same, or even increased? At the end of the three-year period, they will look at the program's effectiveness based on decreased impact of rooting - its frequency, distribution and intensity - and decide whether to continue and expand the effort.
      Although pigs have caused damage or have been spotted in preserves ranging from Sierra Azul to Pulgas Ridge, nowhere has the impact been greater than in Long Ridge. For unknown reasons, the pig population seems to have increased dramatically in the area from Saratoga Gap north into Long Ridge since they were first spotted three years ago. Isaacs speculated that the pigs have moved in from the nearby state parks, where pigs have been a presence for many years. Big Basin has had a moderate pig population for at least fifteen years, and possibly longer. No population studies have been done yet, said Isaacs; the numbers are less important than the impact of rooting. So far, no other preserve has been as heavily impacted than Long Ridge. Part of the push to control the pigs is the high visibility of the damage in Long Ridge; the Preserve seems to be at the edge of an expanding range of a stable population MROSD hopes that they will be able to slow the northward spread. By contrast, in Rancho de Guadalupe, an MROSD property not yet open to the public, pig damage in 1998 was severe, yet in 1999, very little damage was seen; Isaacs speculated that the population is much less stable, perhaps due to other pressures, including hunting by local landowners.
      The other factor in choosing Long Ridge is its popularity. By contrast, pigs have been present in Sierra Azul OSP since before the District acquired the land, but their impact has been less clear - in part because the chaparral that covers much of Sierra Azul masks the pig damage - but also because many fewer visitors see the damage and call for control. Since MROSD is a public agency with an elected Board of Directors, public pressure on the Board influences which programs the District will undertake.

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