It’s been a week since the last full moon on 15^th July. During this time, the odds of being attacked by a lion are highest than at any other point in the month, which is why I’ve been walking around the neighbourhood with two guard bears and a platoon of ninjas. The fact that I live in a leafy suburb of London is inconsequential. You can never be too careful. Constant vigilance.

Of course, lion attacks are more of a problem in other parts of the world. In Tanzania, lions have attacked more than a thousand people between 1988 and 2009, and eaten around two-thirds of them. Now Craig Packer from the University of Minnesota has shown that the frequency of these attacks is tied into lunar cycles.

Texan-born Packer first visited Tanzania in 1972 to study baboons with Jane Goodall. When he returned to the country in 1978, his attention had shifted to lions and it has never left. His team expanded upon records of local lion prides that began in the 1960s, creating a massive set of data on over 5,000 individuals from the Serengeti National Park and the Ngorongoro Crater. By tracking females with radio collars, Packer’s team even has daily records for some prides, including details of their health, location, and even the size of their bellies.

That last piece of information came in particularly useful in their latest study. Packer showed that the lions’ bellies are at their largest on the days closest to the new moon (when it’s totally dark) and smallest close to the full moon. This makes sense – contrary to the bright scenes of most nature documentaries, lions do most of their hunting at night. They’re most successful in pitch darkness and indeed, Packer’s team is more likely to find a pride feasting on a kill in the mornings surrounding a new moon.

In the light of a full moon, killing is tougher work, and lions compensate by scavenging more often and hunting round the clock. Even with these shifted strategies, their bellies still shrink, which means that in the days after a full moon, lions are at their hungriest.

These days also create the ideal conditions for a surprise attack. When the moon is waxing (on its way to becoming full), it rises before the sun sets. But when the moon is waning, there are several hours of darkness between sunset and moonrise, creating the perfect window for a hungry, stealthy hunter.

Packer found that lion attacks on humans are most common during this window. He reviewed government records of every attack since 1988, he interviewed survivors and families of victims, and he visited over 500 attack sites. He found that lion attacks are two to four times more common in the days after a full moon than in the ones before it, and that most people are attacked in the window of darkness between 6pm and 10pm.

The time of year also matters. During the wet season between November and May, the nights are cloudier. During these months, lions are three times more likely to attack people during the dark window after the full moon, than they are during the dry season.

Today, the threat of lions may be confined to certain parts of Africa today, but Packer points out that these cats were once spread throughout the entire world. Humans have co-existed with them and other nocturnal hunters for our entire evolutionary history.

Packer suggests that these dangers might help to explain the role of the full moon in human folklore, and its associations with illness, madness and monsters. As he writes, “The full moon accurately indicates that the risks of lion predation will increase dramatically in the coming days. [It] is not dangerous in itself but is instead a portent of the darkness to come.”

Reference: Packer, C., Swanson, A., Ikanda, D., & Kushnir, H. (2011). Fear of Darkness, the Full Moon and the Nocturnal Ecology of African Lions PLoS ONE, 6 (7) DOI: 10.1371/journal.pone.0022285

Photo by Schuyler Shepherd

More on lions:

• Older elephants know the best anti-lion moves
• How many people did the man-eating lions of Tsavo actually eat?
• How the cat that got the cream then drank it
• Lions killed by perfect storm of changing climate, virus and parasites

July 22nd, 2011 by Ed Yong in Animal behaviour, Animals, Carnivores, Mammals, Predators and prey | 5 comments | RSS feed | Trackback >