It is not one event, it is a continuous, roughly 1,000-kilometer circular movement of around 1.5 million wildebeest and several hundred thousand zebra, following rainfall and fresh grass growth across the Serengeti-Mara ecosystem year-round — there is no month when 'the migration' is not happening somewhere, only months when it is somewhere specific and dramatic. The circuit runs, broadly: December-March calving on the short-grass plains of the southern Serengeti and Ndutu, where up to 8,000 calves are born daily at the peak; April-May moving northwest through the central Serengeti as the plains dry out; June-July pushing further north through the western corridor, crossing the Grumeti River; August-October concentrated in the northern Serengeti and Kenya's Masai Mara, where the famous Mara River crossings happen; and November's short rains pulling the herds back south to complete the loop. What surprises first-timers most is that the herds do not move as one block — they fragment into columns that can be 40 kilometers apart, following localized rain, which is precisely why a specialist guide reading current conditions matters more than any generic month-by-month chart, including this one.