The Great Migration is described as an event, like you can circle a date. It's more like a slow year-round cycle, and the key to seeing it is understanding the loop.
The cast is large. Nearly two million wildebeest travel along with hundreds of thousands of zebra and gazelle. They migrate in an irregular circle between the Serengeti in Tanzania and the Masai Mara in Kenya in search of rain and the new grass that grows after it falls. There is no leader and no map. The herds are guided by instinct and weather, hence the slight variation in timing each year. Reading that timing well is where a Kenya-based safari operator earns its keep.
The section most people want to see is the river crossing. The herds migrate to the Mara River on the Kenyan side from about July to October and must cross. There are crocodiles in the water waiting months for this. The banks are steep sided. Wildebeest congregate, pause, increase in numbers, and then stampede across in a frenzy of dust and splashing, with predators working the flanks. A crossing may take minutes or hours and no guide can guarantee a crossing on any particular morning. The herds decide.
The shape of the year that leads to the crossing makes it possible. Calving occurs much further south in January and February when the plains are green and half a million calves are born in a few weeks. Predators eat, but there are so many that most calves survive to walk north. The herds move up through the Serengeti in the middle of the year and by mid-year the vanguard is at the Mara. As the rains increase further south in late October and November, they are drawn back and the loop begins again.
This means that for a traveller, the calendar is a tool, not a guarantee. The Kenyan window for river crossings is July through October, with August and September being the best months. Arriving in that window puts you in the right place. The rest is done by weather and herd mood. Anyone who sells a guaranteed crossing on a fixed date is selling nature short.
The Masai Mara is worth a visit even outside the crossing months. It has one of the highest lion densities in Africa, as well as leopard, cheetah, elephant and buffalo, meaning that the Big Five are always on the cards, no matter the time of year. The migration is just a drama on top of a rich reserve.
The experience is more influenced by practicalities than people think. Entry fees to the Mara vary by season, and are higher during the peak migration months, so it's important to plan for this. The number of vehicles also increases, and the quality of your guide and the time of your drives are important. The difference between being at the river early and late is everything.
The selection of the base inside or near the reserve influences the amount of action that is captured. Camps further in the reserve or in the private conservancies adjacent to it will place you nearer to the herds and further from the day-trippers. A safari company based in Kenya, which operates the Mara on a regular basis, will know which camps are close to the crossing points in a particular season, and can place guests accordingly, which no brochure can.
The migration is also a feast and the predators are half the story. Lions, leopards, cheetah, hyena and crocodiles all make their year revolve around the herds. The Mara is one of the densest lion populations in the world and when the wildebeest come, the lions become bold and fat. The crossings attract crocodiles which have been waiting for months and the drowned and injured provide food for scavengers for days afterwards. When you watch a crossing, you are watching an entire food web switch on at once, and even if the crossing attempt fails and the herd loses heart and turns back, it is worth the wait.
How long to allow is the practical question. One morning at the river is a roll of the dice, as the herds may not cross that day. Three or four nights in the Mara during the season gives several chances and turns the odds in your favour. It also allows for the other part of the reserve on days when the river is not in flood, and no morning is wasted.
At a crossing, responsible viewing is more important than anywhere else. If there are too many vehicles at one location, they can block the herds' access to water and prevent or delay a crossing. Good guides never stand between the animals and the river, keep engines quiet and hang back from the bank. It is not only ethical to select an operator whose guides adhere to these limits, it is also a better bet, as a herd that feels hemmed in will not cross. It's the animals that set the terms, the drivers who understand that see the most.
There are some myths that need to be retired. The migration is not a one-day stampede that comes and goes. It's a continuous process of grazing, walking and occasional crossings that lasts for months. The animals do not have a set path to the metre. And the crossing points change year to year as the river changes and the herds test different banks.
The best way to watch the migration is to think of it as a wildlife show that you have set up for yourself, rather than a show that has a start time. Select the season, select a base close to the action, hire a guide who knows how to read the herds and allow a few days instead of one. If you do, the chances of being on top of the Mara River while thousands of wildebeest are on the opposite side are definitely in your favour.
One of the few remaining natural spectacles of this magnitude. When you see it in person, with the noise and the dust and the tension on the bank, it resets what you thought a wildlife sighting could be.