Study Debunks Theory That Killing Predators Reduces Livestock Losses

Killing predators such as wolves, mountain lions and bears in order to protect livestock may have intuitive appeal, but a rigorous review of multiple studies that was published today shows little or no scientific support that it actually reduces livestock losses. In fact, in some cases it even leads to increases in livestock loss. These conclusions directly counter the reasoning behind the common practice of killing predators in response to livestock depredations -- as carried out by the secretive federal program, Wildlife Services, and many state game agencies.

"This study shows that not only is Wildlife Services' annual killing of tens of thousands of wolves, coyotes, bears, bobcats, cougars and other animals unconscionable -- it's also ineffective," said Michael Robinson of the Center for Biological Diversity. "Our government should ground the aerial snipers, pull the poisons and remove the steel leghold traps in response to these findings."

The unexpected finding that carnivore killings can increase depredations is likely based on disruption of the predators' social dynamics -- namely, by removing dominant animals that maintain large territories, these killings release sub-adult animals that are less-skilled hunters and thus more likely to target domestic animals.

The new review, "Predator Control Should Not Be a Shot in the Dark" -- published in one of the world's top scientific journals, Frontiers of Ecology and the Environment -- evaluated the methods in 24 previous studies of responses to predation on livestock and catalogued them according to their adherence to the scientific method.

The review found few studies that met accepted standards for scientific evidence. Half of the evaluated studies -- conducted in North America and Europe -- did not follow an experimental design that included control (non-manipulated) herds of livestock and other standard scientific safeguards to exclude the effects of bias in sampling, treatment, measurement or reporting. However, the review found 12 studies that were conducted according to the scientific method. Most of the tests of lethal methods showed no effect or unexpected increases in livestock deaths. Non-lethal methods were found to be safer and more effective.

Two of the studies that used sound methods found that non-lethal measures, specifically guard dogs and fladry (ribbons attached to fences to scare predators away from lambing pastures), were effective at deterring livestock depredations.

The study was conducted by Adrian Treves of the University of Wisconsin, Miha Krofel of the University of Ljubljana in Slovenia, and Jeanine McManus of the University of Witwatersrand in South Africa.