Predator control should not be a shot in the dark, the title of a new study by Adrian Treves and colleagues in Frontiers in Ecology and the Environment recommending policy makers suspend predator control efforts that lack evidence for functional effectiveness and that scientists focus on stringent standards of evidence in tests of predator control.
In his review of the Treves study in Science, Ben Goldfarb explains:
On August 5, biologists from the Washington Department of Fish and Wildlife ascended in a helicopter to shoot two members of the Profanity Peak wolf pack, which had been preying on cattle in the state’s northeast corner. After the cull failed to end predation, the state removed four more members of the 11-wolf pack. Some conservationists were outraged, but the logic behind such lethal control seems airtight: Remove livestock-killing wolves, coyotes, bears, and other predators, and you’ll protect farmers and ranchers from future losses.
However, Treves claims much of the research underpinning that common sense notion is flawed—and that the science of predator control needs a methodological overhaul. Treves a conservation biologist at the University of Wisconsin, along with colleagues examined more than 100 peer-reviewed studies, searching for ones that randomized some by removing or deterring predators while leaving others untouched. Not a single experiment in which predators were killed has ever successfully applied this randomized controlled design. “Lethal control methods need to be subjected to the same gold standard of science as anything else,” Treves says. He argues that policymakers should suspend predator management programs that aren’t backed by rigorous evidence.
Lethal control has long been a staple of wildlife management. Eurasian lynx have been culled by hunters in Norway, wolves killed in Spain and Sweden, jackals and caracals eliminated in South Africa. In the United States, predator control often falls to the federal APHIS Wildlife Services, a branch of the U.S. Department of Agriculture. In 2015, the agency killed 385 gray wolves, 284 mountain lions, and more than 68,000 coyotes. Unlike the Profanity Peak wolf pack, which wasn’t targeted until it began killing livestock, coyote populations in many states are subject to preemptive thinning.
Although removing carnivores to ease livestock loss makes intuitive sense, Treves and other scientists were skeptical: For instance, some research suggests that coyote populations subject to culling have higher pup survival rates, and that male cougars expand their ranges in response to hunting.