The wildebeest herds are in the Serengeti ecosystem all year; the month decides where. According to the park authority's calendar, they calve in the south from January to March, move through the centre in April and May, cross the Grumeti in June and July and the Mara in August and September, and are back in the south in December. At Ndutu, in the Ngorongoro Conservation Area, the calving runs from late December to March. The authority stresses that the timing can shift.
The Ngorongoro Crater is accessible all year. The dry season runs from June to October and the rainy season from November to May, when migratory birds arrive. The crater rim lies above 2,200 m (7,218 ft), and nights are always cold, coldest from June to August. In the Serengeti the tracks are gravel and clay, partly impassable in the rainy season, and the low season from 15 March to 15 May has the lower fee.