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Animal and Plant Health Inspection Service
U.S. Department of Agriculture

Expanding Feral Swine Populations

Population estimates for the number of feral swine in the continental United States vary; however the National Feral Swine Damage Management Program (NFSDMP) states that between 5 and 6 million feral swine exist in at least 35 states.

 In the recent paper “Interpreting and Predicting the Spread of Invasive Wild Pigs”, Nathan Snow and his NWRC, Texas A&M University-Kingsville, and Yale University colleagues modeled the spread of feral swine in the continental U.S. from 1982 to 2012. They found that, during this period, the rate of  northward range expansion by feral swine accelerated from 6.5 to 12.6 km per year. If this trend persists, feral swine are predicted to reach most counties in 30 to 50 years.

 Study results also showed that the spread of feral swine was largely associated with similarities between existing and new habitats. Basically, feral swine were more likely to expand their range into areas that were similar to the ones they currently occupied. The most notable exception was the tendency for feral swine to spread into areas with colder winters, something that is also reflective of their northward expansion. In recent years, the spread also has been associated with trends of milder winters. 

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