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.
|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.