The theory behind how the migration works is simple: seasonal
rains and the availability of grazing determines the "clockwise"
movement of the migration in the larger Serengeti eco-system that
includes Tanzania's Serengeti and Kenya's Masai Mara. A few
physical barriers like the Simiti and Lobo hills, the Grumeti and
Mara rivers hinder and alter this "circular" path.
Well in reality it's not quite that simple!
So here's a more informed explanation on how the migration
really works...courtesy of Richard Knocker:
The wildebeest want to be in the short grass plains of the
southern Serengeti [in Ndutu/Gol/Southern Loliondo] but the water
and grazing cannot support them all year round. This is where they
choose to give birth to their young (usually Feb - March), with the
rich grass to support them. Within a relatively short space of
time, perhaps 4 to 6 weeks, several hundred thousand calves will be
born and this is where we see much of the dramatic predator action.
The Migration will move off in search of sustenance in response to
periods of dry weather, but they will leave this area as late as
possible and come back as soon as they can. This means that every
year is different and, in fact, every week can be
The Migration is also not a continually forward
motion. They go forward, back and to the sides, they mill around,
they split up, they join forces, they walk in a line, they spread
out, they hang around. You can never predict with certainty where
they will be; the best you can do is to suggest likely timings,
based on past experience - but you can never guarantee the
So, soon after the short rains start, we would expect
them to be in, or close to, the short grass plains area (centred
around Naabi/Ndutu/Gol) from December through to April. Depending
on local rainfall, they might be anywhere from Moru Kopjes through
to the slopes of Ngorongoro.
From May, the rains stop and the herds gradually start
moving: generally, as the plains of the south and east dry out,
there is a movement to the north and west, where there is more
grass and more dependable water.
Not all the wildebeest and zebra will follow the same
route: this means that, while part of the migration will head to
the western corridor and the GrumetiRiver before proceeding north,
significant numbers may also go up through Loliondo, or via
Seronera and Lobo.
In a dry year, the first wildebeest could be near the
MaraRiver (the only decent permanent water in the ecosystem) in
early July; in a wet year - mid August. If conditions are very
good, i.e. there is plenty of grass and water; the herds will be
spread out all the way from Seronera to the Mara
The Migration as a whole need not all pass into Kenya
and many stay behind or cross and re-cross the border areas. This
carries on through till October/November, when they will start
thinking of heading back. Again this will be dependent on the
The river crossings happen at any time during this
time of year, but are elusive, rapid and unforgettable
The areas the wildebeest cover are vast, even when
crossed in a 4WD car.
The groups may be spilt over a wide area and finding
one on the brink of crossing is not a given.
The wildebeest are also easily spooked by real or
imagined threats. They fear crossing the river, as they have an
inkling that something lurks there.
Patient waiting near a herd by the river may only
produce a puff of dust as they turn on their heels and run away. Or
maybe the herd is just not ready to cross the river and they are
milling around contentedly.
But if everything is right then, there is utter and
extraordinary chaos as the herds struggle to get to the other side
of a major river filled with crocodiles.