The wildebeest migration which takes place between Kenya's Masai Mara and Tanzania's Serengeti National Park is known as the greatest natural show on earth. Twice a year over two million animals including hundreds of thousands of wildebeest, zebra, Thomson's gazelle and buffalo migrate in search of greener pastures. The best time to experience this migration is between June and August when the wildebeest cross the Grumeti and Mara rivers with their hungry crocodiles. The exact dates of the migration change from year to year, and the herds spend a few months in the Masai Mara before gradually heading back to the Serengeti in December and January. Most tourists watch the show from a four-wheel drive vehicle but an exciting option is to ride alongside the wildebeest on a riding safari or hover above in a hot air baloon.