Extending over 30,000 square kilometres west from the Great Rift Valley to the shore of Lake Victoria, the Serengeti-Mara is the only African migratory ecosystem of comparable scale to have survived unfenced and practically unencroached into the 21st century. To see the endless lines of wildebeest in bleating, snorting, dust-kicking motion as they march determinedly across the plains is one of the world’s most memorable wildlife spectacles.