Mystery of the Man-Eating Lions

A biologist's quest to understand the ecology and behavior of Kenya's notorious Tsavo lions may promote more harmonious relations between the predators and local people

  • Dave Newbart
  • Aug 01, 2004

THE RESEARCHERS sat in a Land Rover just outside southeastern Kenya’s Tsavo East National Park, waiting. Hours ticked by. Nearby, a fresh zebra carcass lay only half eaten.

But the lions that live in this largely unstudied section of the country, unlike wildlife more accustomed to human observers, were wary. Hiding in the thick thornbush that blankets the area, they refused to return to their kill.

It grew darker. Finally, after four hours, one of the lionesses was apparently fed up. With a terrifying, blustering snarl, she suddenly charged. The scientists snapped to attention; they knew of the Tsavo lions’ reputation as oversized brutes. In 1898, two of these predators reportedly attacked, killed and ate 135 men building a railroad across Kenya.

In the end, the lion pulled up just short of the Land Rover. Then the pride’s leader, a male called Cassius, did something remarkable. Accompanying three cubs, he escorted them to the zebra and kept a watchful eye as the youngsters ate. "That is totally unknown in the Serengeti," says biologist Bruce Patterson, lead researcher on a project to study the lions.

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Why Cassius took it on himself to guard the cubs—instead of leaving the task to females in the pride—is anyone’s guess. But it’s not the only mystery surrounding Tsavo lions. Are they, for example, a separate species from Panthera leo living elsewhere on the continent? Why do so many male Tsavo lions lack manes? Are they bigger and more aggressive than other lions? And are the predators really man-eaters? These are the kinds of questions Patterson and his colleagues are attempting to answer about a group of animals that has fascinated observers since their notorious rampage a century ago.

Because they’re far less studied than lions on the Serengeti plains of Kenya and Tanzania, much of what’s known about Tsavo lions is based on speculation, not science. "I’d like to set the record straight about what these lions are really about," says Patterson, curator of mammals at Chicago’s Field Museum and author of The Lions of Tsavo: Exploring the Legacy of Africa’s Notorious Man-Eaters.

SHOWING OFF his kill, Lt. Col. J.H. Patterson (left) sits beside one of two lions he shot in 1898 after the predators allegedly killed 135 laborers building a rail line across Kenya; recent research suggests that he exaggerated the number of victims. All innocence, two cubs (right) play in Tsavo National Park.

Much of the relatively recent interest in Tsavo lions can be traced directly to a display in a back corner of Patterson’s museum. One summer afternoon, a tour group paused outside the glass-and-wood case housing two adult Tsavo lion specimens. Sleek and lean, they look unremarkable except in one way: The lions have no manes. Compared to a typical zoo lion, they look virtually bald. The guide then told the story of the predators’ man-eating spree, a tale that’s been the subject of three books and two movies, including a 1996 feature film, The Ghost and the Darkness.

"Tsavo," the guide began, "means ‘place of slaughter.’" Between March and December of 1898, he said, the two lions in the display case terrorized Indian workers brought by the British to build a rail line from Lake Victoria to the Indian Ocean. By the end of their rampage, the predators had stalked, seized and eaten 135 laborers. Many of the victims were dragged from tents during the night and devoured within earshot of camp. "They ate people like Twinkies," the guide said. "And they killed for pleasure."

Construction at Tsavo was halted until December 1898, when John Patterson, the project’s lead British engineer, finally shot and killed both lions. Patterson (no relation to Bruce Patterson) went on to tour the world, telling his story. Eventually, he sold the lions’ skins to the Field Museum, where they were stuffed and mounted. Viewed by hundreds of thousands of visitors each year, they remain one of the museum’s most popular attractions.

The story of the Tsavo lions remained unexamined for nearly 100 years, when Field Museum scientists began to look into it. In 2000, researcher Tom Gnoske discovered that the railroad office in London had records of only 28 deaths of foreign workers. Though it’s possible that the lions killed many more Africans—whose deaths were not recorded—there’s no evidence that the total reached John Patterson’s claim of 135. "It’s part of the myth," Gnoske says.

A LION CUB (left) perches on a zebra that was killed by its mother. Some researchers suggest that an outbreak of rinderpest between 1891 and 1893 may have wiped out some of the predators’ usual prey, forcing them to turn to humans. Resting his chin on a branch, a short-maned male (right) naps.

Gnoske and his colleagues also explored whether the lions might have had an inherent taste for human flesh. On the contrary, they found that the predators may have been forced to attack people when an outbreak of rinderpest between 1891 and 1893 decimated buffalo herds, their usual prey. Scavenging along the Tsavo caravan route, the lions would have found bodies of dead or dying slaves abandoned by ruthless slave traders. Other bodies were left more or less exposed by local burial practices. Lions are quick learners, and it would not have been a big leap to then turn to living humans.

Another possibility is that a nagging toothache could have led at least one of the predators to prey on people. A radiograph image of one specimen’s skull reveals a severe root tip abscess. "Any sort of pressure on the area would have been extremely painful,’’ Patterson says, making it difficult for the lion to deliver a "killing bite" to either the nape or throat of prey. Humans, no doubt, presented a less taxing meal.

Though no people-eating rampages have been reported since the late 1800s, conflicts between man and beast continue. Records from the Kenya Wildlife Service show 112 attacks on cattle, sheep or goats between 1994 and 1998 in Tsavo East, one of two parks within a larger protected area. During that period six humans were also attacked—and two were killed. The problem is worse outside the parks. On the 96,000-acre Taita Ranch and another nearby ranch, where Patterson currently conducts research, lions attacked livestock nearly 300 times between 1996 and 1999. Across the entire 1.5 million-acre zone surrounding the protected area, lions attack livestock as often as once per day, estimates Steve Turner, a trustee for Kasigau Conservation Trust, which is working to create a wildlife corridor between parks.

And there are still reports of human attacks. In June 2002, for example, lions killed a herdsman along a highway to the coastal city of Mombasa. Usually, however, such assaults are more fatal to the predators than to people. So-called "problem" lions are routinely captured or shot. One animal control officer from Tsavo reported shooting 222 lions across Kenya over 12 years. "Conflict with humans is the number one mortality factor for African lions," says Roland Kays, mammal curator at the New York State Museum and a partner in Patterson’s research.

Many locals still believe that old and sickly lions, possibly with tooth problems, are responsible for most human attacks today. While that might have been the case in the 1898, Field Museum researchers have found that attacking lions these days are typically under five years old and healthy.

Another hypothesis Patterson’s team is exploring is whether Tsavo lions have elevated levels of testosterone. More hormones might lead males to vigorously defend larger territories, leaving less room for youngsters. It could also lead to a condition similar to male-pattern baldness in people, when testosterone receptors on hair follicles are overloaded and cause hair loss, contributing to the absence of manes on the lions. Patterson and colleagues are now collecting hair follicles for analysis by a British endocrinologist.

Testosterone might also explain another phenomenon: single males living with larger prides. In a survey of the lion population of Tsavo East, Patterson and Kays found that average pride size was 7.4 lions compared to 6.4 in the Serengeti. And Tsavo prides typically had just one male, while those in other areas tended to have two or more. How would individual males fend off large groups of wandering males? "It’s still a mystery to us," Patterson says. "But if they had more testosterone they might be aggressive enough to hold onto a pride."

That theory is at odds, though, with research conducted by University of Minnesota biologist Craig Packer, a leading expert on Serengeti lions, and his former student Peyton West. These scientists note that castrated lions, or lions with injuries to their genital regions, lose their manes. Other lions without manes are typically younger or sickly and almost always subordinate to maned males.

Regardless of hormone levels, environmental factors likely play a greater role. Gnoske and biologist Julian Kerbis Peterhans of the Field Museum and Roosevelt University in Chicago compiled data on lions from 300 different locations. They found that the higher the altitude and cooler the temperatures, the bigger the manes. "There are other factors involved but we think the most important one is this temperature business," Kerbis Peterhans says.

Another variable is water, or its severe shortage over long periods of time. In a part of Tsavo East where maneless lions are common, annual rainfall is just 12 inches. On Taita Ranch, however, there is significantly more rain. There lions like Cassius feature what Patterson calls a modest mane: a mohawklike growth on the head, hair on the neck and chest, but bare shoulders. In parts of the Serengeti, where all males sport full manes, annual rainfall can be nearly four times as much as it is in Tsavo.

RESTING in the shade, three lions (right) take refuge from the intense heat. One theory holds that absence of manes is an adaptation that helps the predators stay cool. In Tsavo National Park, two maneless males (left) groom each other to remove burrs and parasites.

Unable to cool down during the dry season—which can last four to six months in Tsavo—a maned lion would be a less efficient hunter, having to skip the hottest parts of the day and remain close to small areas near permanent water sources. That challenge could trigger a hormonal response limiting mane growth. There’s no doubt that a mane makes a lion hot: Thermal images taken by West in the Serengeti show male lions were hotter than females; in Tsavo, maneless males were not hotter.

But West isn’t sold on the idea that manelessness is that prevalent in Tsavo. Because of the harsh climate and thornbush terrain, lions might develop manes later in life, she says, or might continually lose them and grow them back. And they might simply be less regal: "It may be the biggest mane that any Tsavo lion could grow won’t be as big as any mane a Serengeti lion could grow."

While the mane question remains unsolved, Patterson believes he has dispelled other popular ideas about the lions: that they are bigger or possibly a separate species or subspecies of African lion. Charting the skull size of 18 Tsavo lions, he found that they ranged from more than 11 inches to nearly 15 inches—well within the range of lions elsewhere on the continent. And an analysis of the lions’ DNA revealed that their genetic make-up is virtually identical to that of Panthera leo throughout Africa.

Whatever else his research unveils, Patterson hopes his project will help ensure that the lions remain in Tsavo for decades to come. Through Earthwatch Institute, a Massachusetts-based conservation group, volunteers pay fees to visit Tsavo and help Patterson conduct his fieldwork. A portion of their fees goes directly to Kenyan landowners who cut back on grazing, leaving more room for wildlife, including some 30 lions and 200 elephants. Without the volunteers’ contributions, totaling about $35,000 a year, Turner believes the land would be home to "10,000 cows and probably nothing else."

Still, there are limits to this kind of conservation. When a terrorism scare hit Kenya in the summer of 2003, Earthwatch canceled several trips and overall tourism to the country dropped. But Patterson is undeterred. "The battle to save this region’s wildlife," he says, "is going to be won or lost in Tsavo."

Chicago writer Dave Newbart wrote about China’s black-necked cranes for the January/February 2001 International Wildlife.

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