Lions of Tsavo

It is well known that lions ate many of the workers who were building the Mombasa-Kampala railroad. The lions were killed by John H. Patterson who arrived in 1898 to oversee the construction of the rail bridge over Kenya’s Tsavo River. Hundreds of workers fled the site – and construction had halted.

Nine months after his arrival he killed the first one. From nose to the tip of its tail that lion measured 9 feet 8 inches (3 metres) and stood 3 feet 9 inches high. Three weeks later Patterson killed the companion. The lions’ skins were turned into carpets for his flat in England. By 1924 he was broke and he sold the carpets to the Chicago Field Museum of Natural History in the USA. The lions’ skins and heads were mounted on wire forms and until now are displayed in the Museum’s mammal collection.

Nowadays, through stable isotope analysis it is possible to reconstruct the diets of animals by analyzing their teeth, hair, and bones. (Isotopes are atoms of the same element but with different masses because they have different numbers of neutrons.) Isotopes exist in various foods in different ratios, creating a sort of “signature”. Different plants have different signatures. These ratios are passed up the food chain. Therefore the tissues of the body reflect the chemicals in the food and water that are ingested. So for example if a buffalo eats grass, and a lion eats that buffalo, the isotopes from the grass become part of the lions’ tissues. It is possible to analyze what animals were eating, even after they are dead!

To discover what the lions of Tsavo were actually eating, researchers Domini and Yeakel decided to analyze the isotope signatures of a few hairs about 3 centimeters long and a plug of bone from the skulls. The hairs would reveal what the lions had eaten in the previous 3 months; the bones would reveal what they had eaten over their life times. For comparison the researchers also obtained skin and muscle tissue from 5 modern Tsavo lions, bone samples from 25 Tsavo herbivores which would have been the lions normal diet, and bone samples from ancestral skulls of the Taita people, the native people of the area.

Results showed that the Taita people had been eating corn, mbaazi, and the blood and milk of goats. This gave the people a specific isotope signature.

Results also showed that one lion had shifted from a lions’ traditional diet of grass-grazing animals such as zebras and wildebeests, towards leaf eating browsers such as gazelles at the end of its life. The other lion seems to have been eating browsers for most of its life until it shifted its diet to people. During their final three month, humans comprised approximately 30% of one lion’s diet, compared to just 13% of the other lion’s.

The scientists speculate that the lions were companions. They attacked the camp together – but one was after human beings, and the other was focusing on the goats and donkeys.

Why did they change their diets so drastically? It is believed that a sequence of events turned the lions into man-eaters. First, ivory hunters had killed off most of the region’s elephants. Elephants stimulate the growth of grassy savannahs, because they push over trees to eat their leaves. When elephants die, animals that eat grass do poorly – and that is what lions typically hunt. Second, drought and disease had further reduced the population of potential prey. Third, into this situation came a large population of railroad workers. Fourth, one of the lions was in ill health due to broken teeth and major infections on its jaw that probably led to its dependency on soft human prey.

Especially interesting is that the lions were cooperating while eating different prey. It is now understood that individuals of a species can appear identical but actually have different eating habits. Although lions typically hunt together and share the proceeds, cooperation is not just simply related to food sharing. There are other benefits. Territoriality would be one. And perhaps they simply enjoyed being together even though they were eating different things.