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Man-Eating Lions Attack by the Dark of the Moon

If you want to avoid becoming a lion's dinner, keep an eye on the moon. A new study reveals that the big cats are most likely to attack people during the 10 days following the full moon. That's when it's darkest during the hours that humans are out and about at night—and when lions are at their hungriest.

Throughout Africa, people have killed most lions straying outside of nature reserves. Not so in Tanzania, where the big cats still roam freely in many areas. In a huge southern swath of the country, they have been attacking people with regularity. Between 1988 and 2009, lions ambushed more than 1000 people, killing and devouring two-thirds of them.

Ecologist Craig Packer, a lion expert based at the University of Minnesota, Twin Cities, began studying the situation several years ago, motivated, he says, to help protect Tanzanians from truly horrific deaths at the paws of a conservation icon. "No one ever forgets one of these lion attacks," he says. "They're indelibly etched in the memories of the survivors and the family members of the victims."

The attacks, he and his colleagues found, occurred mostly in rural areas inhabited by extremely poor farmers, many of whom sleep in their fields to protect their crops from bush pigs. These nocturnal marauders are just about the only lion prey left in a landscape largely converted to farmland. The lions stalk the bush pigs into the fields, where they sometimes stumble upon easier human prey. Lions hunt best when it's darkest out, and Packer's team wondered whether the amount of moonlight might also play a role in their attacks on people.

The researchers began by analyzing a data set maintained since 1978 on the belly sizes of lions living on ordinary prey in northern Tanzania, outside the man-eating zone. Big, full bellies indicate good meals, and these were hardest to earn as the moon waxed and prey could spot their attackers.

The team also pored over government records of lion attacks and visited 450 sites to interview victims or their families. When they plotted the attack dates against the lunar cycle, a clear pattern emerged. Nearly all attacks occurred after dark, 60% of them between 6:00 and 9:45 in the evening. Most striking, however, was the fact that the attacks were up to four times more likely on the 10 nights after the full moon. During that period, the moon rises later after sunset each evening, so the nighttime hours between 6:00 and 10:00 p.m., when people are most active, are dark. The lions are also at their hungriest because the hunting has been poor.

The bottom line: People living among man-eaters should be careful after the full moon, and they should especially avoid sleeping in their fields, Packer says. His team will incorporate that message into its program aimed at reducing lion attacks by minimizing bush pig crop damage, but he thinks it will be a hard sell. The region's extreme poverty means the urgency of protecting crops will likely outweigh even the risk of being eaten.

The most famous man-eater incident was an 1898 rampage in Kenya by two lions that reportedly killed 135 people (dramatized in the 1996 thriller The Ghost and the Darkness)—a figure that scientists recently cut down to about 35. But lions and other big, nocturnal felines have shadowed humankind since our earliest days. The new research could well explain our fear of darkness and our mythology surrounding the full moon, says Packer, whose group published its findings online today in PLoS ONE. "There's bound to have been an effect of moonlight on our psychology because of these risks," he says. "The full moon definitely is a loud and clear harbinger."

It's remarkable that the lunar cycle plays such a strong role in lion attacks on people, says carnivore biologist Laurence Frank, director of the Kenya-based conservation group Living with Lions and a research associate at the University of California, Berkeley. He points out that in conflicts between predators and people, the predators usually lose because humans simply wipe them out, so any insights that help reduce such devastating interactions will ultimately benefit lions' long-term survival. "Large carnivores are the hardest animals to conserve, just because of the problems they create for people," he says.

But what's true for lions may not be true for another big cat: tigers. In Nepal, tiger attacks on people are much rarer than Tanzanian lion attacks, says Charles McDougal, a wildlife biologist with the United Kingdom-based International Trust for Nature Conservation who has studied tigers in Nepal for 3 decades. And despite their nocturnal habit, he says, tigers almost always attack people during the day, because at night people avoid the forests where they lurk. But India, he points out, has recorded a nighttime rash of man-eating leopards, and they, too, may be ruled by the moon.