New evidence in the long-standing mystery of the Tsavo 'man-eater' lions

In the year 1898, a railroad camp in Tsavo, Kenya was terrorised over several months by a pair of lions who killed and ate an estimated three dozen railroad workers before being shot and killed by Colonel J. H. Patterson. The event is so infamous there's even a movie about it. But one question has remained unanswered all this time: what motivated these predators to hunt humans?

"The original story was that these lions were desperate and eating anything they could, [even] crunching on bones," said Larisa DeSantis of Vanderbilt University in Tennessee. Seemingly supporting this narrative, Tsavo was going through a drought and a rinderpest epidemic at the time, and Colonel Patterson himself described the lions chomping into the bones of their victims.

Colonel John Patterson along with one of the Tsavo lions he shot back in 1898. Image: The Field Museum

But in a new study, DeSantis was able to put this hypothesis to the test. Some time after killing the lions, the Colonel sold their bodies to the Field Museum in Chicago, where they remain to this day, preserved for research. Evidence from the cats' teeth and jaws paints a picture of their diets over the final weeks and months of their lives.

And the evidence doesn't match up with the idea of these predators being desperate for scraps. When animals eat, their food leaves microscopic patterns of damage on their teeth, called microwear. Carnivores that crunch bone, like hyenas or desperate scavenging cats, end up with very recognisable patterns – and these lions simply didn't have them. Their teeth compared well with lions in the wild or in captivity that have plenty of meaty morsels to chew on.

It doesn't look like these lions were starved for lack of food. And a previous analysis of chemical isotopes in their fur and bones revealed that they had been eating a variety of prey besides humans, which suggests they weren't lacking in choices either. So, why make the switch to eating people? The answer seems to be poor dental health.

Left: The more human-hungry of the Tsavo lions, with major dental damage. Right: The jawbone of the Mfuwe man-eater, with injuries consistent with being kicked in the face. Image: Bruce Patterson / The Field Museum

One of the Tsavo lions had such severe dental disease that he had broken a canine, three lost incisors and an abscess. The second lion had less severe injuries, and also appears to have been eating less human prey. Investigation of another "man-eater" lion (it also ate women and children) from Mfuwe in Zambia – which killed about six people in 1991 – showed that it also had a nasty fracture on its lower jaw.

These dental issues, DeSantis explained, "might have challenged how they hunted, might have been painful, and might have also severely impacted their ability to take down large prey." For these pained predators, accustomed to powerful prey like zebras and buffalos, humans must have looked like a much easier option.

A male lion of the Tsavo region. These cats are distinctive because they don't have large manes. Image: Bruce Patterson / The Field Museum

"We don't tend to like to think of ourselves as being on the menu for cats, but we are, and we have been for a long time," DeSantis said. "While man-eating isn't all that common, it's not all that rare, either."

In Tanzania, between 1990 and 2004, a total of 563 people were reportedly killed by lions. Just last year, in the Gir Forest of India, another trio of lions was captured after killing three people. Recent reports have also identified leopards and tigers as hunters of humans. Anthropological records of humans being devoured by cats go back a long way.

For DeSantis, the take-home point here is that we need to keep this dynamic in mind as we move into a future of rising human populations and shrinking natural ecosystems. "There are going to be consequences of increasing one prey source, which is us, and decreasing other prey sources, which are many of the [big herbivores] on the landscape," she said.

As intriguing as the results of this new research are, DeSantis doesn't think the mystery is totally solved. Dental issues don't always match up with man-eating habits, and vice versa. More information will require more research, and for that, museum specimens are critical.

"It's hard to fathom the motivations of animals that lived over a hundred years ago, but scientific specimens allow us to do just that," said study co-author Bruce Patterson (no relation to the Colonel) in a press release.

The modern study techniques used to examine the cats' skulls would have been unimaginable a century ago, DeSantis told me. "And who knows what we'll be able to tell about them one hundred years from now."