The Mara River, nature’s best-laid trap for migratory animals, is the stage for a grandiose spectacle. When food supply in the Serengeti dwindles, the Masai Mara is a paradise for predators. As the black wildebeests, gazelles, zebras, and antelopes make their yearly trip from the south of the Serengeti to the north, nature’s best-laid trap,…