Lions are killing people in Tanzania three times as often as they did 15 years ago, according to a survey. The authors of the study say that farmers should clear their land of bush pigs, an attractive prey to lions, to reduce the number of clashes between lions and local people.

Since 1990, lions have killed more than 563 Tanzanians and injured at least 308, the researchers report in Nature1, with fatal attacks increasing markedly over time.

The problem seems to be the rising human population. In the past, lions have typically hunted wildebeast rather than bush pigs. But as Tanzanian communities have grown, the number of usual prey has diminished.

Villagers have a tendency to sleep in their fields to guard their crops against nocturnal pests such as bush pigs. These farmers cannot afford to buy fences, explains lead author Craig Packer of the University of Minnesota in St Paul.

So the pigs get in to the crops, the lions follow the pigs into the farms, and then the villagers fall prey to the lions. Both farmers and their families are killed: 18% of victims in the study period were younger than 10 years old.

Retaliation

The intensified attacks have also taken a toll on the lions, thanks to people hunting the killers in retaliation. Experts fear Lion populations are now shrinking rapidly.

"They want to kill the problem animals, but it's difficult to know who the problem animals are, so sometimes the response is indiscriminate," Packer says. "The number of lions being killed by people has probably increased by ten fold over the past decade." There are roughly 100,000 lions in Africa, and at least a quarter of these live in Tanzania, he estimates.

The conflict has concerned wildlife biologists. "It is problem number one when it comes to Lion conservation. There's no close second," Packer stresses. He adds that outsiders often have an impression that lions are killed for trophy hunting, but this isn't the main issue. "People outside of Africa seem to have forgotten how threatening these animals are," says Packer.

The new survey provides the first concrete evidence that Lion attacks are worst in areas with bush-pig infestations. Researchers suggest that digging trenches around fields to keep these animals away from crops would reduce the number of lions that follow them into areas with humans.

"There has long been a sense of helplessness in these areas," Packer says. "We are trying to provide fresh ideas."