Tanzania, Oct. 21 -- Saitoti Petro scans a dirt road in northern Tanzania for recent signs of the top predator on the African savannah. "If you see a lion," he warns, "stop and look it straight in the eyes - you must never run."

Petro points to a fresh track in the dirt, a paw print measuring nearly the length of a ballpoint pen. He walks along a few more yards reading tracks the way an archaeologist might decipher hieroglyphics, gleaning meaning from the smudges in the dust. A large male passed here within the past two hours, he says. "Here he's walking slowly, then you see his claws come out in the tracks. Perhaps he's running after prey, or from something else."

The tall, slender 29-year-old is marching with four other young men who ...