Researchers home in on swine habits to fight the invasion

By Joshua Rapp Learn

A feral swine sounder causing erosion by using a wallow on Havasu National Wildlife Refuge property. Removal of these invasive feral swine supports the refuge’s mission of conservation and recovery of native wildlife. ©U.S. Fish Wildlife Service photo

Tracking the destructive habits of feral swine in different parts of North America is giving researchers new ideas about how to stop the invasive animals.

“Pigs have this really great capacity to learn how to use resources,” said Mark Wilber, who was a postdoctoral researcher at Colorado State University and at the U.S. Department of Agriculture’s National Wildlife Research Center when he led a study on feral swine published recently in Ecological Applications.

Two to six million feral swine are believed to persist in at least 39 states and many Canadian provinces. Feral swine (Sus scrofa) cause an estimated $1 billion of damage in the United States every year, including agricultural damage and damage to vehicles that strike the animals. In Mississippi and Louisiana, the invasive pigs even damage levees.

Wildlife managers have developed a number of control methods, including poisoning feral swine with toxic baits and shooting pigs from helicopters, but the species is notoriously hard to control.

“It’s a really, really big issue,” said Wilber, who is now a postdoctoral researcher at the University of California, Santa Barbara.

Now researchers are working to learn more about the ways these animals cause the most damage to crops in an effort to better focus control efforts for the USDA’s National Feral Swine Damage Management Program (NFSDMP).

Wilber and his colleagues examined information collected by the USDA about where crops are planted across the U.S. They overlaid these maps with location and movement data collected from radio collared feral swine to find out if there were particular attributes about crops or the landscape that make them more attractive to swine.

They found that pigs consumed crops more in areas where there were more crops available, which isn’t surprising. But Wilber said the findings show how well pigs can adapt to available resources, so “adding additional resources isn’t necessarily the solution to crop damage” since the pigs would just begin to associate the area with having good food resources. But on the other hand, “when there were more available nonagricultural resources in an area, it reduced the amount of agriculture resources they used,” Wilber said.

Crop type affected pigs’ interest. The researchers found that swine exploited crops like cereals, fruit, nuts and grasses more often, possibly due to their higher nutritional value.

They also found that male pigs ate crops 50% more than female pigs — possibly due to having larger home ranges and being less risk averse.

Wilber said that these results can be used in tandem with in-field measurements of crop damage to predict the risk of damage in areas of the USA that wild pigs are invading.  Areas with more natural resources, for example, are likely to experience less damage.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society. Contact him at jlearn@wildlife.org with any questions or comments about his article.

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