The debate is ongoing; should lethal or nonlethal predator control methods be used to protect livestock? According to logic, if predators are killing livestock, by removing those predators, livestock losses should decrease. However, as there are legal, ethical and ecological risks at stake, common sense may no longer pass as sound justification.
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Research, led by Associate Professor Adrian Treves of the University of Wisconsin, Madison, and published in the Frontiers of Ecology and the Environment, examined more than one hundred peer-reviewed studies of predator control methods and livestock in Europe and North America. Yet, of the over one hundred studies analysed, only twelve met the academic standards from which scientific inference could be drawn; with two reaching ‘gold standard’ and the other ten, a lesser ‘silver standard’.
The results from the twelve studies examined, suggest nonlethal methods of predator control are generally more effective and do not lead to counterproductive consequences.
A variety of predator control methods are used by livestock owners. Lethal methods include hunting, poisoning, kill traps and destroying the litters of young. Nonlethal methods include livestock-guarding animals, fladry (visual deterrents), other types of repellents, fences, diversionary feeding and sterilisation.
Of the one dozen studies analysed, seven examined lethal methods of predator control; two of which appeared to conclude a decrease in livestock loss but only to a minor degree and on a short term basis. In one particular case, it was found that less than one lamb was saved per lynx killed and had negligible practical benefits.
The remaining five lethal method studies concluded either no effect or, in two cases, an actual increase in predation. A study published in 2013 determined that killing cougars resulted in detrimental effects to livestock numbers. Older, male cougars would keep the younger, more aggressive males at bay. Consequently, the hunting of older males, resulted in the immigration of younger males and increased livestock loss.
By contrast, not one of the nonlethal method studies showed an increase in predation. Of the twelve studies examined by Treves and his colleagues, the only two that met ‘gold standards’ examined nonlethal methods which effectively decreased livestock losses through the use of livestock-guarding dogs and fladry, although fladry may be limited to deterring wolves.
One long term and in-depth study, conducted in France, concluded that a combination of mobile electric fences at night and at least five livestock-guarding dogs prevented almost all wolf predation on sheep.
Treves’ critics have suggested that his own study may not be living up to his standards as no independent experts were asked to review the validity of his research. They also suggest that Treves’ expectations of academic standards in predator control research may be impractical as complexities in the field of biology result in most ‘gold standard’ experiments being precluded.
So, what does this mean for the future?
Treves and colleagues have called for a suspension of predator control programs that do not have strong evidence to support their efficacy. They suggest that, like the EU Directive and many U.S. Federal policies, decision-making should be based on clear evidence and as such, until ‘gold standard’ tests have been completed, evidence-based policy should focus on nonlethal methods. However, a major culture shift will also be required amongst ranchers and livestock owners to turn from quick and easy lethal methods to nonlethal predator control.