Can Wild Pigs Ravaging the U.S. Be Stopped?

For centuries wild pigs caused headaches for landowners in the American South, but the foragers’ small populations remained stable. In the past 30 years, though, their ranks have swollen until suddenly disease-carrying, crop-devouring swine have spread to 39 states. Now, wild pigs are five million strong and the targets of a $20-million federal initiative to get their numbers under control.

Settlers first brought the ancestors of today’s pigs to the South in the 1600s and let them roam free as a ready supply of fresh pork. Not surprisingly, some of the pigs wandered off and thrived in the wild, thanks to their indiscriminate appetites.

Wildlife biologists can’t really explain how pigs from a few pockets were able to extend their range so rapidly in recent years. “If you look at maps of pig distribution from the eighties, there’s a lot of pigs, but primarily in Florida and Texas,” says Stephen Ditchkoff, a wildlife ecologist at Auburn University. “Today, populations in the southeast have exploded. In the Midwest and the north it’s grown to be a significant problem.” Ditchkoff believes sportsmen transported the pigs so they could hunt them on their land.

As pigs spread, they wreak havoc on the lands they inhabit. Wild pigs cause at least $1.5 billion in damages and control costs each year, according to a 2007 survey, mostly to agriculture. Dubbed the “rototillers of nature,” they dig up fields, create wallows in pastures and destroy fences. A church in Texas was so worried that pigs would devour its annual pumpkin sale that it lobbied the local government to let hunters stand watch over the patch at night. They were right to fret. The 2.6 million pigs in Texas cause $500 million in damage each year—a liability of $200 per pig. “I’ve never seen any one species that can affect so many livelihoods and resources,” says Michael Bodenchuk, state director of Texas Wildlife Services. He is particularly worried about harm to native species and the 400 stream segments in Texas that are infected with bacteria from the pigs’ defecation.

Heeding concerns from state wildlife agencies, the U.S. Department of Agriculture created a new national program in April to halt and reverse this trend. It aims to wipe out pigs from two states every three to five years and stabilize the population within a decade. Dale Nolte, national coordinator of the program, says his first priority will be states with the fewest pigs; he will then work back to those like Texas that are overrun. One reason he wants to confront the states with the fewest pigs first is because the animals reproduce rapidly once they invade an area. If 70 percent of the pigs in a region are killed, the remaining ones can have piglets fast enough to replace all those lost in just two and a half years.

Those odds haven’t stopped wildlife agents from trying to rid their states of the scourge even before a federal program was in place. Although the traditional methods of hunting and trapping have helped, they have not stopped overall population growth. Practitioners are refining these tried-and-true methods while also exploring new ways to destroy larger numbers of pigs.

Trapping, for example, works well in areas with a low to medium density of pigs but has one major pitfall. Pigs travel in groups of eight to 15 called sounders, and trappers rarely catch all the members at once. Those that escape will learn to avoid traps in the future. Ditchkoff and Mark Smith, an animal specialist at Auburn University, teach landowners to practice whole sounder removal in which trappers patiently bait and rebait traps for days or weeks to improve their chance of capturing the entire group. “It’s not how many pigs you remove,” Smith says. ”The real question is, How many pigs did you miss?”

Another popular way to rid a region of pigs is to hunt them from helicopters. Wildlife agents in Texas have found aerial shooting to be the most cost- effective method of pig control, even though the price can run as high as $600 an hour. Texas agents kill 25,000 pigs a year and half of them are shot at from the sky.

A team in New Mexico is using a hunting approach that employs a “Judas pig,” named for the biblical disciple who betrayed Jesus. They affix a radio collar to a pig and set it free, then follow it to its sounder. After a year of using this method state agents had eliminated 687 wild pigs and wiped them from 10 of the 17 counties where they had once roamed.

Neither aerial shooting nor the Judas pig technique is particularly well suited to the forests of the Southeast or the residential areas on which pigs have increasingly encroached. These limits are why Glen Gentry, an animal scientist at Louisiana State University, would prefer to poison pigs with sodium nitrite. “We can probably get to more of the group with toxicants,” he says. Ditchkoff agrees: “In Texas and Alabama, we need better tools than trapping,” he says. “We need toxicants and contraceptives.”

Gentry hopes to receive some of the money that will be available through the new federal program for his work in Louisiana, a state with half a million pigs. He needs to find a way to convince the pigs to eat bait laced with the bitter sodium nitrite compound and ensure that other animals will not be harmed if they accidentally consume it. Government researchers are also testing sodium nitrite as a pig poison, which has long been an effective form of eradication in Australia. If it works here, poison could be the most cost-effective solution of all.

In addition to devoting money to getting rid of pigs, the new federal program led by Nolte will spend $1.5 million to update estimates of the nation’s wild pig population and investigate the annual damage they inflict. Another $1.4 million will help monitor diseases like swine brucellosis and pseudorabies, both of which have been eradicated among domesticated pigs but threaten to make a comeback. The rest of the money will set up a centralized system to allow federal officials to better coordinate the projects in each state.

Source: Scientific American