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The Trail CompanionSpring 2000Pigs, Pigs and More Pigs...
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![Feral pig in Sunol Regional Wilderness -- click for larger image [127Kb]](newsletter/2000/spring2000/sp2000images/feralpig.jpg)
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| Feral pig in Sunol Regional Wilderness -- click for larger image [127Kb] |
| Photo by
Terry Smith. Reprinted by permission. |
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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