Invasive pigs moving into Oregon

April 27, 2006

CORVALLIS, Ore. – Feral pigs, which are responsible for an estimated $800 million in annual damages to agriculture commodities nationwide, are rapidly expanding their range across Oregon, according to a recent risk assessment conducted by Oregon State University scientists.

Also called wild boars or wild swine, omnivorous feral pigs vary in appearance, but most have hairy coats, thick necks and shoulders and wedge-shaped heads suitable for digging and rooting.

"These animals have the capability to create incredible damage across a large area," said Bruce Coblentz, a fisheries and wildlife scientist in OSU's College of Agricultural Sciences. "One pig on one golf course in one night can cause $50,000 to $60,000 in damages. They are extreme generalists with a capacity for tremendous growth."

The invasive pigs have been recorded in locations throughout southern and central Oregon, and their distribution may continue to spread as global climate change results in warmer temperatures farther north, said Coblentz, who authored the assessment with researcher Cassie Bouska. Feral pigs are most heavily concentrated in Florida, Hawaii, Texas and California. Despite not being native to the United States, their nationwide population is estimated at more than 4 million.

Feral pigs are often introduced into new areas by humans who plan to return and hunt them at a later time, Coblentz said, adding that "the majority of feral pigs in Oregon have been kicked out of the back of a pickup truck." This manner of scattered distribution could explain the animals' recent appearance in central Oregon around the towns of Prineville and Madras, areas Coblentz said were not traditionally thought of as habitable for the pigs.

"They tend to be most successful in warmer, wetter areas and are often found in riparian zones," he said. "It used to be a population would die off due to freezing temperatures, but we're not having winters like we used to, and we're seeing the results in range expansion."

Feral pigs have been reported in nine Oregon counties: Coos, Curry, Josephine, Jackson, Klamath, Wasco, Jefferson, Crook and Wheeler. According to the Pest Risk Assessment for Feral Pigs in Oregon, which was conducted in accordance with USDA Forest Service guidelines, the animals – though currently in isolated populations – could feasibly inhabit any area where food and water are easily available and the habitat provides suitable cover. In the drier areas of the state, populations could exist successfully in riparian areas, and near golf courses, irrigated fields and pastures.

"They are pretty wary beasts," Coblentz said, adding that the Oregon populations consist of feral domestic pigs and feral pig-wild boar hybrids. "Just because they've never been sighted in a region, does not mean they are not living there, competing with native species for resources and habitat. They will aggressively defend food sources, and because of this they pose a significant problem for deer and other wildlife."

Part of the reason that feral pigs are such a risk to the state's economy and environment is because of their reproductive capabilities. Sows reach sexual maturity as early as four months and can produce two litters averaging five young per year. Unchecked, the pigs can spread until they've populated all available areas, said Coblentz, who is a professor in OSU's Department of Fisheries and Wildlife.

"Think of the situation as a lit stick of dynamite," he said. "If you throw it on a landscape one of two things will happen; the fuse will go out, or the stick will explode. Right now an invasion is occurring, but you don't know it because you can't see it."

Oregon agriculture brings in revenues of more than $3.6 billion each year. Many of the state's crops grow in areas and mediums highly attractive to feral pigs, and could be susceptible to disturbance by the invasive animals. Feral pig activity and rooting near roadways and buildings can damage structural integrity and increase maintenance costs. Each year the United States spends less than $1 million a year in control costs for feral pigs.

According to the risk assessment, it is likely that the current feral pig populations in Oregon could be removed with reasonable costs and efforts. However, equally probable is the possibility for the population to grow at such a rate that control methods would be too costly to attempt and would not offer long-term success.

Feral pigs are subject to predation by cougars, bears, coyotes and eagles, however they still manage to thrive when introduced to new areas.

Coblentz recommends that anyone who sees a feral pig, or sees evidence of rooting and wallowing behavior contact their local division of fish and wildlife immediately.

Author: Aimee Lyn Brown
Source: Bruce Coblentz