Anywhere between two million and six million wild pigs (also called feral hogs) roam across 39 states in the US. These pigs are really a hybrid. In the late 1400s and early 1500s European explorers and settlers bound for the new world loaded domestic pigs onto their ships. Once on dry-land, these animals gradually escaped, spread, and then bred with wild boar, another non-native species introduced for hunting purposes. The result is problematic, at least for landowners.
Wild pigs have few natural predators and, with the highest reproductive potential of any mammal of similar size, they are spreading rapidly causing millions of dollars worth of damage as they go. Groups of pigs are known to eat and root up crops, destroy fencing and equipment, push out other wildlife and damage recreational areas. There have even been reports of pigs attacking hikers within US national parks. ‘One of the figures that people have put out there, just in terms of damage to crops, vehicles and cultural damage, is over a billion dollars per year,’ says Mark Wilber, a postdoctoral fellow at Colorado State University. ‘In Texas alone, I believe it’s over $50million a year due to agricultural damage.’
Wilber and colleagues from the US Department of Agriculture have been working to determine exactly how the pigs are utilising agricultural crops. To do so he and the team analysed roaming data from more than 300 pigs collared with GPS trackers and overlaid this with maps of crop distribution. The results of the study were largely in line with predictions. The pigs appeared to eat and damage agriculture more when it was highly available, while this behaviour lessened when non-agricultural food sources were also in high abundance. Less predictable was the finding that male pigs were 20 per cent more likely to damage crops than females – the hypothesis being that without child-rearing responsibilities, the males have more freedom to roam and engage in risky behaviour.
The team now aims to use this information to predict where pigs might spread to in order to establish new populations. ‘This can also help us estimate costs to agricultural systems and start looking at how to mediate the damage that is done,’ says Wilber.
However, this doesn’t solve the problem of how to reduce the population. The most common method across the US is currently lethal removal, with some people in favour of the pigs for the hunting opportunities they offer. Many states allow hunters to kill wild pigs year-round without limits, making them the second-most hunted species in the country. Thousands more are shot from helicopters. But despite these efforts, the pigs seem to bounce back. With a 2017 study predicting that the animals could inhabit most counties in the continental US within three to five decades, this uncomfortable relationship is unlikely to get any more peaceful.
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