A recent study came to a counter-intuitive conclusion: The more wolves killed to protect livestock, the greater the frequency of livestock attacks.
Washington State University wildlife biologist Rob Wielgus and data analyst Kaylie Peebles wanted to test the efficacy of lethal control programs used on predators. Such programs are commonly used to keep predator populations under control and livestock safe, but the scientists say, in a release, that they represent a "widely accepted, but untested, hypothesis."
The researchers found that with every wolf killed the chance of livestock attacks increases significantly. They noted that this probability trend line continues upward until 25 percent of wolves in a population are killed, at which point livestock depredation begins to level off.
Wielgus and Peebles write that such a level of lethal wolf population control "is unsustainable and cannot be carried out indefinitely if federal relisting of wolves is to be avoided." For the lethal control of wolves to result in the protection of livestock, then, the animals would wind up right back on the government endangered list.
The researchers studied 25 years of U.S. Fish and Wildlife Services lethal control data on wolves across Montana, Wyoming and Idaho. It turned out that with each wolf killed, the odds of sheep depredations rose 4 percent and for cattle deaths 5 to 6 percent in the following year. And, when 20 wolves were killed, they noted that livestock deaths doubled.
All of this, of course, begs the question why. How could killing more wolves result in more livestock deaths?
The researchers suggest that killing wolves probably disrupts the social structure of a wolf pack. When pack numbers decrease, particularly among alpha males and females that normally keep younger offspring from mating, more wolves are freed up to breed. That increases the number of breeding pairs. When those pairs have offspring, it results in more mouths to feed. And because the new parents are bound to one place, due to having pups, they can't hunt in as wide a range and may be more likely to hunt accessible livestock instead of seeking out deer or elk.
Wielgus and Peebles argue that while lethal control programs may sometimes be necessary in short-term situations, non-lethal programs -- such as guard dogs, horseback range riders, and use of "risk maps" ranchers can consult to keep livestock clear of wolf-rich areas -- should also be considered. To underscore his point, Wielgus said his Large Carnivore Lab monitored 300 sheep and cattle in Eastern Washington's wolf country over the summer and none of the animals were killed by wolves.
"The only way you're going to completely eliminate livestock depredations is to get rid of all the wolves," Wielgus said, "and society has told us that that's not going to happen."
The study has just been published in the journal PLOS ONE.