The story goes that in 1898, two male lions in Tsavo, Kenya, formed a coalition and begun eating railway workers - between 28 and 135 of them. After 9 months of attacks, a British field engineer and Officer, Lt. Col. Patterson, hunted down and killed each lion. I'm willing to guess this made him a very popular man. Somehow, these animals eventually ended up in the collection of the Field Museum of Natural History, where people could oggle the Man Eating Lions.
We're supposedly confident that Patterson definitely got the right lions, since the attacks stopped, but how much of the lions' diet was humans? Well, the old phrase that "You are what you eat" is literally true, and different sources of food leave different isotopic signatures. This allows scientists to go in and assay the isotopic ratios to find out what categories of diet an animal ate, and the relative dietary ratios. Using potential prey items as references, they found that one of the lions was eating humans 30% of the time, when it was eating at all. Here's the abstract:
Cooperation is the cornerstone of lion social behavior. In a notorious case, a coalition of two adult male lions from Tsavo, southern Kenya, cooperatively killed dozens of railway workers in 1898. The “man-eaters of Tsavo” have since become the subject of numerous popular accounts, including three Hollywood films. Yet the full extent of the lions' man-eating behavior is unknown; estimates range widely from 28 to 135 victims. Here we use stable isotope ratios to quantify increasing dietary specialization on novel prey during a time of food limitation. For one lion, the δ13C and δ15N values of bone collagen and hair keratin (which reflect dietary inputs over years and months, respectively) reveal isotopic changes that are consistent with a progressive dietary specialization on humans. These findings not only support the hypothesis that prey scarcity drives individual dietary specialization, but also demonstrate that sustained dietary individuality can exist within a cooperative framework. The intensity of human predation (up to 30% reliance during the final months of 1898) is also associated with severe craniodental infirmities, which may have further promoted the inclusion of unconventional prey under perturbed environmental conditions.