A continuous record of lion life
Since 1966, researchers in Tanzania's Serengeti National Park have maintained the world's longest continuous field study of a large mammal. The Serengeti Lion Project, started by biologist George Schaller, has tracked the lives of individual lions across more than twelve generations. This long-term monitoring provides an detailed record of the species' behavior, social structure, and population dynamics. The project continuously monitors about 24 prides, which amounts to roughly 330 individual lions in the Serengeti study area.
Researchers use a combination of direct observation and technology to follow the prides. Beginning in 1984, radio collars were fitted to at least one female in each pride, allowing teams to locate the groups on a daily basis. This consistent contact is important for recording births, deaths, social interactions, and territorial disputes. The data collected has produced one of the most extensive datasets on any mammal, including life histories for over 5,000 lions since the project began. The work was significantly expanded by Craig Packer, who directed the project for 35 years starting in 1978.
The brutal logic of infanticide
One of the project's most significant findings is the prevalence and purpose of infanticide. When a new coalition of males ousts the resident males from a pride, they systematically kill the unweaned cubs. Data from the project shows that this practice accounts for 27% of all cub mortality in the first year. For cubs under nine months old at the time of a pride takeover, the mortality rate approaches 100%.
This behavior is a reproductive strategy. A lioness will not become receptive to mating while she is nursing cubs. By eliminating the previous males' offspring, the new males trigger the females to enter estrus again, sometimes within a few weeks. Without this, they would have to wait up to two years for the cubs to be weaned.
Female lions do not passively accept this. They will fiercely and cooperatively defend their cubs from intruding males, although they are not always successful. The social life of lions, from the cooperative bonds between lionesses to the violent competition between males, has been documented in detail for decades by the project's dedicated field biologists.