Environment

Does Dental Disease Push Big Cats to Prey on Humans?

One of the infamous lions of Tsavo suffered from a debilitating abscess that may have been the cause of its macabre diet.

John Patterson with one of the man-eating lions of Tsavo. Credit: The Field Museum

John Patterson with one of the man-eating lions of Tsavo. Credit: The Field Museum

Researchers have known of the bad state of man-eating lions’ dental health for at least two decades. Now, they have revealed that one of the infamous lions of Tsavo suffered from a debilitating abscess that may have been the cause of its macabre diet.

Over the course of nine months in 1898, two large cats named The Ghost and Darkness picked on labourers constructing the railway line connecting Mombasa, Kenya, with Kisumu, on the eastern bank of Lake Victoria in Uganda. When fear of the lions stopped work on the Lunatic Line, as the British press referred to it then, engineer and lieutenant-colonel John Henry Patterson shot the cats. Although the railway company put the toll at 28 Indian labourers, Col. Patterson claimed the cats had killed 135 workers in a famous book he wrote about his exploits, The Man-eaters of Tsavo (1907).

The skulls and skins of the two Tsavo lions are preserved at the Field Museum of Natural History, Chicago. In 2009, scientists used the stable carbon-to-nitrogen ratios, an analytical technique, of hair and bone to estimate that the lions ate no more than 35 people in those nine months. The researchers say a lack of animal prey drove the lions to feast on humans. This was plausible since a rinderpest epidemic had wiped out wild and domestic animals at the time.

Lions prey on ungulates, eating the flesh and crunching the bones. “I could plainly hear them crunching the bones, and the sound of their dreadful purring filled the air and rang in my ears for days afterwards,” Col. Patterson wrote. He describes hearing the duo of lions nosily grinding bones outside his tent and at the stakeout where he sat over the remains of a donkey.

But did he really hear them chomping on bones?

Chewing bones leaves telltale traces on the teeth. Larisa DeSantis of Vanderbilt University created casts of their teeth and examined them for microscopic wear and tear in 3D. In addition to the two Tsavo lions, she also investigated the skull of another lion reported to be a man-eater from Mfuwe, Zambia. Then she compared them with the dental sets of wild and zoo lions. She discovered the man-eaters’ teeth were not as worn out as was a normal wild lion’s enamel.

“The microscopic wear of the lions’ teeth were less complex and ‘chewed up’ than you’d see in an animal that eats lots of bone, like a hyena. Instead, their dental microwear is similar to what you’d see in a zoo lion,” DeSantis said in a press release.

“It’s a fantastic piece of work using highly advanced and varied scientific techniques,” said Ravi Chellam, who studied lions in Gir in the 1980s and is currently the executive director of Greenpeace-India. “It’s a very good example of how scientific investigations can provide us with data that advances our understanding of complex issues and enables us to gain informed insights that would otherwise not be possible.” Chellam wasn’t involved with the study.

The skull of the first Tsavo man-eater. Credit: Bruce Patterson and J.P., The Field Museum

The skull of the first Tsavo man-eater. Credit: Bruce Patterson and J.P., The Field Museum

One of the two Tsavo lions indulged in man-eating more than the other. An infection at the root of a canine tooth would have made gnawing on hard objects like bones painful. The Mfuwe lion endured a fractured mandible. The infected root canal and fracture were likely sustained from a kick of a large prey animal during a hunt.

“These injuries may have been decisive factors influencing their consumption of humans,” write the researchers. Their paper was published in the journal Scientific Reports on April 19, 2017.

Since humans may have removed the remains of the deceased the next morning, the lions perhaps didn’t get a chance to get to the bones. But only one of the two lions had a bad toothache. The other suffered minor injuries that didn’t interfere with his hunting abilities. According to the carbon isotope study, this lion continued to hunt zebra, cape buffalo and East African oryx and would have had ample opportunity to chew on bones. So why didn’t his teeth show any signs of heavy wear and tear? The study doesn’t offer answers.

The lack of heavy wear and tear on the teeth also shows the lions ate only soft tissue for the last three months of their lives.

“Human bones are much smaller and probably less tougher than that of wild ungulates,” says Chellam. “As a result, feeding on human bones is unlikely to result in the same levels of dental wear and tear.  This aspect has not been considered while interpreting the data. I would also think that it would not be easy for lions to have separated the flesh from the bones while feeding on human bodies, especially from the upper limbs.”

Could such infirmities drive carnivores to preying on humans? Jim Corbett blamed broken canines and injuries from porcupine quills for turning tigers into man-eaters. Today, wildlife managers and researchers in India often cite his reasoning to explain man-eating – even though it has little scientific basis.  

In 2001, two researchers, Julian C. Kerbis Peterhans and Thomas Patrick Gnoske, wrote, “Man-eating is not a guaranteed outcome of the serious trauma affecting the predatory behaviour of large pantherids.” As an example, they cited the Pipal Pani tiger in Corbett’s The Man-eaters of Kumaon (1944). Even after a buffalo gored and seriously wounded the tiger and a local hunter had shot it in the shoulder, it didn’t take to killing humans.

Peterhans and Gnoske examined specimens of lions held at the Field Museum of Natural History, the National Museums of Kenya, the Milwaukee Public Museum and the United States National Museum. They write that some of these lions suffered worse dental problems than the main Tsavo man-eater. Although some had severe skeletal ailments, none of these lions were reported to be man-eaters. In fact, a radio-collared lioness killed an adult eland even though her canines were totally worn out. She didn’t gum it to death, but she may have easily broken the neck or suffocated it. This shows lions don’t need canines to kill their prey.

“Our data suggest that only 15% of disruptive lions (including man-eaters) are so impaired,” Peterhans and Gnoske wrote.

Another study, after examining data from the Ugandan archives, says only 14% of attacks on humans were caused by injured lions.

The Tsavo lions. Credit: John Weinstein, The Field Museum

The Tsavo lions. Credit: John Weinstein, The Field Museum

Lions seem to run a high risk of injury in bringing down large prey animals that buck and kick, so a fair number of man-eaters may be afflicted. Do dental problems cause man-eating? Or are they coincidental?

“Young lions have little or no damage while progressively older lions show more and more [injuries],” says researcher Patterson. “However, crippling dental disease is rare. Superficial examinations of damage are poor indicators of the extent to which functionality is hindered. The root-tip abscess was only detected by X-ray exam, something missing from any of the [previous] analyses.”

However, Craig Packer of the University of Minnesota isn’t convinced. “A tooth abscess isn’t the reason for [a lion] becoming a man-eater. You have lots of man-eating leopards and tigers in India, and like most man-eating lions, they have perfectly good teeth!”

He cites two key criteria: whether the lions have enough natural prey and whether people are unusually vulnerable (for the cats to turn on humans).

Patterson agrees that opportunity and lack of prey are key factors in provoking lion attacks on people and livestock. The arrival of railway workers provided the opportunity – “but evidence shows that dental disease was the trigger that tipped the scales,” he says.

The Indian countryside is overrun by livestock and feral animals. Any predator that doesn’t have access to choice wild ungulates can pick from a range of domestic prey, from dogs to cattle. The lions of Gir certainly don’t know the difference between wild and domestic. Given half a chance, they take cattle as they would sambhar or nilgai. Nor do the 100 lions that live in villages around Gir see their human neighbours as easy prey.

“It is remarkable how low the number of attacks by large cats are on people,” says Chellam. “These attacks often have clear patterns in terms of space and time, an indication that these attacks are likely a result of the aberrant behaviour of one or may be a few large cats. Wild cats, in general, fear humans and try their best to avoid them. Most attacks – accidental or provoked – do not result in deaths of the people attacked. Even when people are killed, not all human bodies are eaten by the wild cat. These point to different motivations driving and influencing the behaviour of wild large cats with respect to human beings they encounter.”

The painful infection, lack of animal prey and opportunities notwithstanding, humans made up only 30% of the main Tsavo man-eater’s diet, according to the carbon isotope study. “This publication [examining dental wear] does not suggest that the man-eating lions were primarily dependent on humans as a food source,” stresses Chellam. “This is very important for us to understand that even man-eating wild cats continue to prey upon wild ungulates and other prey animals.”

If we are not an important source of food, why do man-eaters target people at all? That’s the million dollar question that defies easy answers.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.