Tanzania's oldest and most popular national park and also a world heritage site and one of the Seven Natural Wonders of the World, the Serengeti is famed for its annual migration, when some six million hooves pound the open plains, as more than 200,000 zebra and 300,000 Thomson's gazelle join two million wildebeest as they search for fresh green grasses.  But even when the migration is quiet, the Serengeti still offers some of the best game viewing in Africa as it is home to a huge number of resident herbivores and predators who survey and protect their territories.