The crossings on the Mara River in Kenya, occur any time between mid July and late September. They are not guaranteed and in some years they may not occur at all, it’s all weather dependant. The best years to see a crossing in the Mara are drought years, when food is limited and the majority of the herds head north and into Kenya. In a year with good rains the herds can be spread out from the Mara, south into the Serengeti of Tanzania.
To experience a crossing is a test of patience, and one can wait 4 to 5 hours for a crossing to occur (you can also be lucky and witness one in minutes). When they do happen, it’s spectacular, as thousands of wildebeest lunge into the murky river and dodge the crocodiles waiting an easy meal. It’s life and death.
There is no set pattern to the migration, though ultimately the wildebeest want to be on the short grass plains of the southern Serengeti. This is where the grass is most nutritious. However there is no permanent water down there in the dry season, so they are forced to move to better pasture and water, which the Masai Mara can provide.
Once they arrive in the Mara they only stay until they sense rains are falling in the south, then off they charge again. Again it’s all about rainfall, with the short rains coming in October and November. They also don’t move in one mega herd (there’s a million wildebeest); herds of thousands are the norm, and some herds stay longer in the Mara than others.
The best areas to see the herds heading south (October/November) is also along the Mara River, though on the Tanzania side in the northern Serengeti.
It’s a sight worth seeing, though also popular, so essential to book your camps well in advance for the July/Aug/Sept period.