One of East Africa's most amazing sights is the Great Migration, a year round movement through the Serengeti-Mara ecosystem of nearly 2 million animals - Wildebeest, Zebra and Gazelles. However the pattern and timing of the migration varies from year to year, as the animals search for grass and water. So where does the migration begin? For the Wildebeest, or Gnu as they are also known, life is an endless journey. The only real beginning is the moment of birth. Generally Wildebeest mass on the calcium rich short grass plains in the southern part of the Serengeti ecosystem during the rains from November to May. Here on these ancestral calving grounds, ninety per cent of the calves are born within a few weeks between January and March - 400,000 calves, a truly spectacular sight. This peak in calving ensures that the majority of calves survive as predators such as Lion, Hyena and Wild Dog can only devour a small percentage of the newborns. The tawny coated calves can run within a few minutes of birth. By the end of May most of the vegetation on the short grass plains has been eaten and drinking water has become scarce. The huge herds begin their trek to the north and the west across the long grass plains to the open woodlands. These great concentrations of Wildebeest are a sight to behold, the sounds of the great herds echoing across the plains. The Zebra often lead the way, as they eat the stems and the seed heads of the long grass. The Wildebeest follow, preferring the shorter grass. Around this time the mating or rutting season begins. The normally placid Wildebeest bulls establish and defend territories, herding the females as they wander through. The bulls go through highly ritualized challenges, pawing the ground, bucking and snorting, dropping their knees with their foreheads flat on the ground, horn to horn in an impressive display. There is nothing visible to mark their territory except the bulls themselves. By late June the rut is over and the bulls merge once more into the amorphous life of the herds. One of the main barriers in the path of the migration is the Mara River. Traditional crossing places are returned to year after year. However, what might have been an easy crossing the previous year could, due to heavy rains, have become unsuitable the following year. To see a river crossing is a truly dramatic experience, with thousands of Wildebeest and Zebra massed along the banks waiting for the moment to cross. Finally - sometimes after hours of waiting - one of the animals will make a move and the others follow, regardless of danger, be it sheer cliffs or Crocodiles lurking below. By October or early November the herds head south again, back to the Serengeti. Long columns of Wildebeest, the females, heavy with calves, trudge along in single file, sometimes walking, sometimes running. By December they are back on the short grass plains of the southern Serengeti and so the age-old cycle continues. Although this implies a degree of predictability about the behavior of the Wildebeest herds, movements are dictated by the vagaries of rainfall and the subsequent availability of food. What one can say with certainty is that the Wildebeest migration is the world's finest game viewing experience played out in East Africa's premier wildlife destination - the Serengeti - Mara.