Seen from the air, they ripple across the landscape — a river of antelope racing across the vast grasslands of South Sudan in what conservationists say is the world's largest land mammal migration.
The country's first comprehensive aerial wildlife survey, released Tuesday, found about 6 million antelope. The survey over a two-week period last year in two national parks and nearby areas relied on spotters in airplanes, nearly 60,000 photos and tracking more than a hundred collared animals over about 46,000 square miles (120,000 square kilometers).
