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University of Minnesota
July 21, 2011
A Tanzanian who survived a lion attack poses with her children and researcher Hadas Kushnir.
In Africa, a full moon portends real danger of lion attacks
By Deane Morrison
From werewolves to wackiness, folklore abounds with tales of peril associated with the full moon.
Pure lunacy? Maybe not. A team of University of Minnesota ecologists has found that lion attacks on people in rural Tanzania vary with the lunar cycle, a discovery that may be the first scientific underpinning for full-moon legends.
But there's a twist: The night of the full moon is actually the safest night. The danger jumps on the nights immediately following the full moon because that's when the lions are hungriest and evenings—when people are still active—are darkest.
"Our key finding is that the night of the full moon is very special—it is the last night of safety for people who are primarily exposed to lion attack in the evening," says lead researcher Craig Packer, a professor of ecology, evolution and behavior at the University. "Thus, the full moon is not dangerous in itself but is instead a portent of the [evening] darkness [and attendant danger] to come."
The study focused on 474 victims from 450 attack events between 1988 and 2009 in southeastern Tanzania. It is published in the journal Public Library of Science ONE.
Stories behind the statistics
To piece together the relation between phases of the moon and lion attacks, the researchers gathered data on the timing of attacks and how hungry lions were at various points in the lunar cycle. (They estimated hunger across the lunar cycle from data on belly sizes of lions in the Serengeti and Ngorongoro Crater areas of north-central Tanzania.) Co-author Hadas Kushnir, who was a graduate student of Packer, visited sites of attacks in southeastern Tanzania and talked to survivors and families of victims as part of her doctoral research on human ecological causes of attacks.
The number of people attacked (fatalities plus survivors) in rural Tanzania between the hours of 6 and 10 p.m. from 1988 to 2009. Full moon occurs about 14.5 days into the lunar cycle.
In the two districts she surveyed, most attacks occurred in agricultural areas, where Tanzanians often sleep in huts of thatched grass or palm fronds from which they can guard their fields. But hungry lions, both male and female, have no trouble breaking in and killing people to eat.
"Stories could be difficult, says Kushnir. "We became close to a man who told how a parent and stepparent of his and two of his kids were sleeping in the field in a makeshift hut when a lion broke in and killed them all."
Attacks also occurred along paths as people walked to get water, and were even common in the centers of villages.
"In one case we met a boy who was about 7 years old and had been just outside his house making a fire, Kushnir recalls. "A lion came and grabbed him. But his father ran after the lion and chased it off. "
On the other hand, young men who had survived attacks could be very macho about telling their stories, she notes.
Kushnir, along with Tanzanian field assistant and co-author Dennis Ikanda, often slept in tents in lion country, "so it was a little scary sometimes," she says.
The deadliest time
In tropical regions like Tanzania, the sun drops like a stone over the horizon, leaving only a short period of twilight. Even in summer, night has fallen by 7 p.m., Kushnir says.
A hut used by Tanzanians to keep watch on their fields at night. Photo: Hadas Kushnir
But people's days aren't finished. They cook outdoors, visit neighbors and use outdoor toilets—all occasions that put them at risk of attack in the evening hours. In rural Tanzania, people generally remain active from 6 to 10 p.m.
As for lions, the going gets rougher as the moon waxes. In the days just before full phase, the moon is up most of the night, and at full moon it rises at sunset and is up the entire night. That makes it hard for lions to catch any kind of prey, and attacks on people plummet. Lions' shrinking bellies indicated that they grew hungrier as full moon approached.
The tables turn right after full moon, however. On the following night, the moon rises about 50 minutes after sunset. Each night it rises later, lengthening the interval of evening darkness. The prey-deprived lions take advantage of this window of opportunity, and nighttime attacks—60 percent of which occur between 6 and 10 p.m.—skyrocket (see chart).
Evenings remain dark for more than two weeks after full moon, until the first quarter of the next lunar cycle. Thus, the weeks just after full moon are the most dangerous to people. Hourly attack rates were two to four times higher in the first 10 days after full moon than in the 10-day period before full phase, the researchers found.
Lions get very hungry as the full moon approaches. Photo: Craig Packer
Packer notes that humans have always lived close to large nocturnal carnivores. But during the sunset-to-sunrise interval, people have tended to be most active in evening and to subsequently sleep in shelters. Therefore, historically, the days after full moon have been most perilous.
Lions, however, don't pose nearly the threat they used to, as an expanding human population has taken its toll. Even so, the large felines of the world may have left our imaginations "aglow at the sight of the full moon," says Packer.
"Big cats are disappearing fast all over the world, but their evolutionary impact on our psychology will likely persist forever."
Besides Packer, Kushnir and Ikanda, graduate student Alexandra Swanson of the Department of Ecology, Evolution and Behavior also contributed to the study.
Published in 2011