Talk to any wildlife biologist in the southern United States about wild pigs, and you’re likely to hear something akin to at least one of the following, “They’re the four-legged equivalent of fire ants;” “If the average litter is six, typically eight survive;” “Only a fence that will hold water will hold feral hogs.” Even the most rigorous scientists are reduced to using these tongue-in-cheek aphorisms to describe the harsh reality and seemingly apocalyptic future of North America’s second-most harvested mammalian game species, reports the Wildlife Management Institute.
No other domesticated animal becomes feral so easily and survives more adaptively than the swine. Often labeled the “ultimate generalist,” the pig’s spread throughout North America via a biological trifecta of high reproductive potential, climate tolerance and ability to re-organize entire ecosystems has resulted in something not unlike a pandemic. According to those who have witnessed the wild pig’s march across the continent, the invasion is best characterized as an “ecological train wreck.”
Forty-five states and four Canadian provinces are currently grappling with the environmental and financial calamity brought about by the feral, wild or hybrid pigs within their borders. Though population estimates are difficult to determine, most experts believe that North America is home to between three and six million wild pigs.
“They can live in just about any habitat; anywhere from the Canadian Prairie Provinces down to the deserts of Mexico and all parts in between,” said Dr. Jack Mayer, research scientist and manager at the Savannah River National Laboratory. According to Mayer, three distinct types of wild pigs reside in North America. First is the feral pig, originating from domesticated stock brought to Florida by Hernando de Soto in the mid-1500s. Second is the pure Eurasian wild boar, introduced to the continent by hunters in the late 1800s. Last is the hearty, hybridized hog, resulting from crosses of the two parent strains. Wildlife managers collectively refer to all three types of invasive swine simply as wild pigs.
The feral pig/wild boar hybrid is by far the most prolific of the three strains and likely the most adaptive. “Virtually every habitat in North America is represented in the wild boar’s native range in Eurasia,” notes Dr. Ben West, the western region director for the University of Tennessee Extension. “Thus, there is huge genetic potential in the hybrid pig.” According to West and other wildlife biologists, the hybrid wild pig’s ability to adapt and thrive in habitats of all major ecosystems in the United States is likely unlimited and largely unknown.
The wild pig’s capacity to increase its numbers and expand its range is unparalleled among North America’s invasive mammals. Females are capable of reproducing at six months of age and can produce up to three litters a year. Though the typical litter averages six, sows can give birth to as many as a dozen under good conditions. Surprisingly, female pigs can breed well into their teens; researchers have documented pregnant sows as old as 14. This reproductive proficiency combined with an absence of natural predators has allowed many wild pig populations to double in as little as four months.
According to data collected by the Southeast Cooperative Wildlife Disease Study, wild pig populations in the U.S. have irrupted in the last 30 years. In 1982, 475 counties in 17 states contained wild pigs. By 2004, the number of counties reporting wild pigs had risen to 1,014. Based on current estimates, those numbers are on a fast track to double again in the near future. As prophesized by one Texas Parks and Wildlife game warden, “There’s only two kinds of folks—those who have hogs and those who will have ‘em.”
Given the level of ecological and agricultural destruction currently being waged by hogs, the future cost of managing their swelling populations will pose a major challenge to already fiscally strapped state fish and wildlife agencies.
Recent estimates of the damage done to natural and agricultural resources by wild pigs approach $1.5 billion annually, with heavily infested states such as Texas suffering nearly $52 million of swine-caused wreckage every year. The bulk of the damage stems from the pigs rooting through vegetation and soil in search of roots, tubers, invertebrates and crops. The resulting tilling effect destroys agricultural land, disturbs native plant communities, causes erosion and, as is the case in Hawaii, creates standing water hollows that serve as breeding grounds for non-native mosquito species. According to the U.S. Geological Survey, the explosion of disease harboring mosquito populations in Hawaii has had a devastating effect on the island’s already declining native bird populations.
The wild pigs’ destructive feeding behavior poses a particular threat to sensitive wildlife species and their habitats. According to studies by researchers at Texas A&M University, wetlands and riparian areas suffer the most damage from wild pigs. In some areas, nearly 50 percent of the habitat is significantly degraded by the hogs’ rooting and wallowing. Additionally, these wet areas also are experiencing increased bacterial contamination in the form of E. coli and fecal coliform from the ever-present pigs.
“Hogs are deadly to anything that nests on the ground,” stated West. “One of the best examples is the depredation of sea turtle eggs on Ossabaw Island.” Before the Georgia Department of Natural Resources (GDNR) began an intensive wild pig removal program on Ossabaw, a barrier island south of Savannah, sea turtle nests on the islands’ sandy beaches suffered greater than 30 percent mortality. Today, as a result of the GDNR removing nearly 3,000 hogs from the island annually, those nests experience less than 5 percent mortality.
Interestingly, researchers also documented a significant increase in the body weight of Ossabaw’s white-tailed deer following wild pig reduction efforts. This fact, along with other research conducted in southeastern hardwood forests, demonstrates that wild pigs present a formidable source of competition for dozens of native wildlife and plant species. Largely due to the pigs’ habit of bulldozing seedlings and rooting for mast crops, such as acorns, these forested areas are experiencing dramatic change. Hardwood regeneration has nearly halted and many wildlife species are outcompeted for critical resources.
Unfortunately, the wild pig’s impact on native mammals is not restricted to increased competition or habitat destruction. Hogs harbor numerous diseases as well as internal and external parasites that are transmissible to wildlife, livestock and even humans. Many of these diseases, such as brucellosis, tuberculosis and the pseudorabies virus have been the target of national disease-eradication programs for livestock. As wild pig numbers continue to increase and spread to new areas, biologists are concerned that their efforts to eradicate or reduce the prevalence of these diseases in wild and domestic animals will be in vain. In addition, researchers at the USDA National Wildlife Disease Center note the possibly insurmountable challenge of controlling an “accidental or intentional outbreak of a foreign animal disease, such as foot and mouth, rinderpest, African swine fever or classical swine fever” if those diseases were ever to find their way into the wild pig population.
To date, no single technique used to control the spread or overall numbers of wild pigs has proven successful—a fact not lost on disease specialists and wildlife managers. According to West, 50 to 70 percent of a wild pig population must be removed each year to stabilize or begin reducing it. Unfortunately, hunting and other lethal control methods account for only 20 percent a year on average. Even more frustrating to wildlife managers is the fact that hunters are the one’s largely responsible for the viral spread of wild pigs to new geographic regions across the country.
Given that the wild pig is listed as an invasive animal in most states, hunters are presented with a nearly unlimited and often year-round season during which to harvest hogs. This, unfortunately, has led many individuals to shuttle and re-stock wild pigs illegally into new areas. In an interesting and somewhat contradictory move in 2009, several states, including Kansas and Nebraska, actually outlawed the hunting of wild pigs in an effort to halt their spread. By eliminating the opportunity to hunt, these states hope to remove the incentive to introduce wild pigs. Time will tell if the effort proves successful.
Currently, significant research is being conducted on swine-specific toxins to aid in the control of wild pigs. Ironically, the most promising of these new products, commercially known as Hog-Gone®, is a concentrated form of sodium nitrite, the most common pork preservative used worldwide. While initial results look promising, it is likely that no silver bullet exists to rid North America’s diverse habitats of the wild pig. According to West and other wildlife biologists, only constant monitoring and unified efforts between hunters, landowners and wildlife management agencies can protect native ecosystems from the invasion of the wild pig. In the words of Michael Bodenchuk, State Director of the Texas USDA Wildlife Services, “We’re not going to barbeque our way out of this problem.”
Learn more regarding wild pigs and their management. (mcd)