The best time to see the Great Migration is from June to October when the herds are crossing back and forth between the northern Serengeti and the Masai Mara. It’s the best time of year to see dramatic river crossings but is also the busiest time of year. November to March, Tanzania’s ‘green season’ is far quieter, and from January you’ll see the herds grazing with newly born calves. The long rains between April and May make this the only time of year less suited to seeing the huge herds of wildlife on the move.