Generally wildebeest mass on the calcium rich short grass plains in the southern part of the Serengeti plains. Here on these ancestral calving grounds offering, ninety percent of the calves are born within a few weeks between January and March - 400,000 calves, a truly spectacular sight. While the short grasses offer good visibility against predators, 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.
Most of the vegetation on the short grass plains has been depleted and water has become scarce. Along with the arrival of the long rains, the herds begin their annual journey north across the long grass plains to the open woodlands. The zebra often lead the way eating the stems of the long grass while the wildebeest follow, preferring the shorter grass. The bulk of the herds head up through the western corridor, and their progress is slowed by the Grumeti River. Around this time, the mating or rutting season begins. The bulls establish and defend territories, herding the females as they wander through while challenging other males by pawing the ground, bucking and snorting, dropping their knees with their foreheads flat on the ground, horn to horn in an impressive display.
After making it across the Grumeti River, the herds continue across the Grumeti area towards the Northern Serengeti en route to Kenya's Masai Mara. By the end of June, the rut is over and the bulls merge once more into the amorphous life of the herds. By late July the masses have typically reached one of the main barriers in the path of the migration, the Mara River.
During this period, most common for Mara River crossings, the bulk of the migration is found in the far north Serengeti and the Masai Mara. Traditional crossing places are returned to year after year. To see a river crossing is a rare and 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. Yet despite the confusion and the losses, the majority of the wildebeest survive. Witnessing a crossing is impossible to guarantee and requires both patience and luck.
By late October or early November, the short rains come and 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. Typically traveling along the eastern side of the Serengeti ecosystem and in the Ngorongoro Conservation Area, they are returning to the short grass plains in the south, where the circle of life begins all over again as it has for millennia.