'Predators are the best wildlife managers, ' writes George Schaller. They weed out the sick and old and keep herds healthy and alert. Yet the large predators of the world have been and are still being exterminated because they are thought to harm wildlife. Schaller's award-winning work, based on three years of study in the Serengeti National Park, describes the impact of the lion and other predators on the vast herds of wildebeest, zebra, and gazelle for which the area is famous.