I’ve been thinking a lot about pigs lately, which seems
crazy for someone whose job is to “protect, enhance, and restore the native
biodiversity of Tejon Ranch.” As most of
you know, the pigs on Tejon Ranch and throughout California are not native, but
are an Eurasian species introduced to North America by people. (These feral pigs are not to be confused with
the javelina or peccary, native to the Americas but in a different family.) So
why am I spending so much time thinking (and worrying) about a nonnative
species? Because like many nonnative
species, feral pigs have the potential to cause negative impacts to the native
species that we are trying to conserve and, in the case of pigs, we suspect the
magnitude of these impacts to be extreme.
Feral pigs (also called wild pigs, hogs, Eurasian wild
boars, Russian boars) were first brought to the Americas by European explorers
and settlers. Some animals escaped
domestication or were intentionally released into local habitats as a fresh
meat supply. Over the centuries periodic
human-introductions and the natural expansion of established feral pig
populations have resulted in a very broad distribution. Feral pigs are currently found in at least 38
U.S. states, and in California, they are known to occur in 56 of the State’s 58
counties. At Tejon Ranch they can be
found in virtually every habitat, ranging from open arid grasslands, to dense high-elevation
forests and chaparral, and even into Joshua tree woodlands and other desert
habitats.
Why are pigs such a concern?
They really are a terrifyingly fascinating species. Pigs are omnivorous, meaning they eat just
about anything, including bulbs or tuberous plants, acorns and other fruit
(including agricultural crops), game species such as ground-nesting birds
(quail) or new-born deer fawns, and reptiles and amphibians, some of which are probably
special-status species. So feral pigs
eat or compete with many of the native species that the Conservancy is charged
with protecting. They root for much of
their diet and can severely damage habitats in the process. To make matters worse, feral pigs are an
extremely productive species. A female pig can start breeding at less than
1-year old, and have two litters each year with as many as 8 or more piglets
per litter. Talk about exponential
growth! There are currently no effective
birth control methods available for feral pigs.
The icing on the cake is pigs are extremely social, smart and wily, quickly
learning to minimize their exposure to hunters and traps. There is even a story from the feral pig eradication
project at Santa Cruz Island of pigs “playing dead’ until hunters passed by. Great, zombie pigs.
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| Pig rooting in a large population of striped adobe lily (Fritillaria striata), a species of concern. It seems they are sparing that plant in favor of others (Dichelostemma sp.?) Photo courtesy of Mike White |
So what are we going to do about pigs? The short answer is “we don’t know yet.” To help sort out our options, the Conservancy
commissioned a just completed study of feral pigs by a Masters group from the
Bren School of Environmental Science and Management at UC Santa Barbara. The Bren group’s work has helped to frame the
problem and describe potential tools available to manage it. We don’t believe that it is currently
feasible to eradicate feral pigs from Tejon Ranch, which leaves us with two
primary options: 1) exclude pigs from
high value areas of the Ranch (e.g., wetlands, special status species habitats)
with fences, or 2) reduce the size of the population on the Ranch to a level we
can live with. Excluding pigs requires buying
and installing lots of pig-proof fencing and the associated long-term maintenance
of the fencing. By its nature, this
approach also requires prioritizing specific resource areas that would be
fenced over others that would not.
Reducing populations means killing lots of pigs − unfortunately no other option is really practical
at this time. Preliminary population
modeling conducted for the Conservancy by Dr. Kyran Kunkel suggests that pig
population control is potentially feasible but very high harvest rates are
required. Oh, did I mention that pigs
are considered a “Big Game” species by the State of California? This means that hunters must treat this
highly destructive and invasive species in the same manner they would other
native big game species in the state (think deer and elk), potentially limiting
the ability of hunters alone to control feral pig populations.
To better understand the situation at Tejon
Ranch, Conservancy Wildlife Technician, Ben Teton, has initiated field
monitoring of pig abundance and their ecological damages. We are hoping Ben’s hard work provides us with
a scientific foundation of pig ecology on the Ranch, and a measure of how the
Tejon Ranch Company’s successful pig hunting program may serve as a model element
of a successful control program. We
would also like to initiate some pig exclosure experiments in the near-term to
see if we can better understand the specific impacts to native biodiversity
caused by pigs to help formulate realistic management objectives. In the meantime, we will keep evaluating
which adaptive pig management strategies have the biggest bang for the buck, I
mean pig.
