Tourists riding safari tour vehicles watch a herd of Wildebeest gather in a field during the annual wildebeest migration through the Massai Mara National park in Western Kenya on August 15, 2008.  According to the African Wildlife Foundation (AWF) the largest mammal migration in the world is that of the Serengeti wildebeest.  Wildebeest are grazers and are constantly on the move in search of grass and water. The AWF says that these animals make a migratory circle of 500 to 1,000 miles each year, beginning right after the calving season in January and February on the southeastern Serengeti plains, moving west toward Lake Victoria, then turning north into the Maasai Mara. They are relentless in their advance and many are injured, lost (especially calves) or killed. By the end of the dry season, the wildebeest have almost exhausted the grazing lands and return south to the Serengeti plains as the rains begin. Kenyan Tourism Minister Najib Balala told AFP "I believe in the next five years, we should have a plan for five million people coming to Kenya," he said, adding that he was encouraged by the early response from tourism professionals and tourists in Kenya's main markets. The highest number of tourist arrivals achieved by Kenya was in 2007, when two million people visited the east African country, renowned for its wildlife safaris and sun-drenched Indian Ocean beaches.     AFP PHOTO/Roberto SCHMIDT