It is one of the oldest conflicts between man and beast: farmers killing marauders such as wolves, lynxes, lions and leopards to defend their livestock from the predators. This ancient tension has increased as people have encroached ever further into the wilderness, and many predators have been driven to the verge of extinction as a result.
Wolves were nearly wiped out in the US in the last century, leaving just 4000 today. Norway has considered culling up to a quarter of the 80 or so wolves in southern Scandinavia to appease farmers who claim they are killing their sheep.
And numbers of Africa's great predators, notably lions, cheetahs and hunting dogs, are in free fall as they are shot, poisoned and snared by people with whom they come into conflict (New Scientist print edition, 20 September 2003).
Yet the slaughter may be unnecessary. The first worldwide review of the effect of predators has found little evidence that they have a significant impact on livestock. "There's this cultural hangover that says predators are bad and killing them is the only way to deal with the problem," says lead author Kate Graham of the University of Stirling, UK.
But the study showed that there is not enough data to draw any firm conclusions about the impacts of predators on livestock, or to evaluate any benefits from culling them. "We just haven't gathered the evidence to say that there is a real problem," Graham says.
The few studies that do bear scrutiny show that in areas home to animals such as lions, wolves, jaguars and snow leopards, the predators are responsible for no more than 3% of livestock losses. And the number of predators in a particular area seems to have little effect on the number of livestock killed.
Adrian Treves of the Wildlife Conservation Society in New York found a similar result when he reviewed case studies of culls of predators including cougars, wolves and bears. Killing the animals cut livestock losses on only one-third of ranches and farms, and any benefit generally lasted no more than a year.
These results will be published in a book in 2005. "We just don't know very much about individual predators' behaviour around livestock," Treves says, "which really hampers our ability to design non-lethal controls."
Death or Disease:
Graham's review found that attention often focuses on the most conspicuous predator, and few studies account for the number of livestock that fall prey to other predators or disease. For example, in Spain hunters persecute the threatened red kite because it kills rabbits.
But 28 other predator species eat rabbits too. One study reviewed found that just 2% of cattle in Zimbabwe succumbed to predators, while 23% died from disease.
However, ranchers still believe that predators have a huge impact, and sometimes with good reason, says lion expert Bruce Patterson of the Field Museum of Natural History in Chicago. For while most wolves and cougars stay away from people and their property, some lions are habitual livestock raiders.
And while lions in Kenya kill just 2.4% of cattle herds each year, costing ranches about $9000 or 2.6% of their income, that is no comfort to subsistence farmers with just a few animals, who may lose their entire herd. People's attitudes to lions are more likely to be based on their community's experience than scientific reports, he says.
Conservation biologists and wildlife managers agree that the way to resolve these conflicts is to start generating accurate models of what carnivores are eating, and then try to turn the animals' attention away from livestock. By exploiting that knowledge, it should be possible to find ways to help people tolerate the presence of large predators.
To find out more about the impacts of predators, Andrew Beckerman, a co-author of the review now at the University of Sheffield, UK, would like to see controlled experiments on managed ranches and wildlife reserves. He says this may reveal ways to keep both livestock and predators safe.
Journal reference: Biological Conservation (DOI: 10.1016/j.biocon.2004.06.006)