In November, April, May and June the migration is “in between” locations and as such these months are slightly transitional times to see the herds. November is the short rains, April and May are the long rains and as such the grass is green in these months across the Serengeti, so the wildebeest are more dispersed than in the prime time of July – October and December – March. Thus, you don’t get as many of those condensed big herds which people get excited about!