Size: 14,763 Sq. Km. --as big as Northern Ireland or Connecticut-USA. Serengeti is the most popular wildlife sanctuary in the world. Serengeti's low vegetation means that game viewing is relatively easy. It varies from grass plains in the south, Savannah with scattered acacia trees in the center, hilly wooded grassland in the north, to extensive woodland and black clay plains to the west. There are many small rivers, lakes and swamps and "kopjes" scattered about. Animals live in absolute freedom on endless plains.

The Serengeti Migration The endless plains of east Africa are the setting for the world’s greatest wildlife spectacle - the 1.5 million animal ungulate (wildebeest) migration.From the vast Serengeti plains to Masai Mara (Kenya). Over 1.4 million wildebeest and 200,000 zebra and gazelle, relentlessly tracked by Africa’s great predators, migrate in a clockwise fashion over 1,800 miles each year in search of rain ripened grass.

There is no real beginning or end to a wildebeest's journey. Its life is an endless pilgrimage, a constant search for food and water. The only beginning is at the moment of birth. An estimated 400,000 wildebeest calves are born during a six week period early each year - usually between late January and mid-March. This spectacle takes place in Serengeti National Park / Ngorongoro Conservation Area.
Even discounting the migration the Serengeti is superb. But the migration puts the park in a league of its own. It is, quite simply, the greatest wildlife show on Earth. Two million animals at times, mostly wildebeest and zebras, moving around an ecosystem 25,000 sq. km. in area, almost as big as the state of Massachusetts. But a lot wilder.
At its most spectacular the Serengeti migration is one of the few experiences that really justify the word “awesome”, but to see it you have to know where and when to go, and it isn’t as predictable as some people might think, though over a period it does follow a fairly regular pattern. We will assume on this web-site that we are talking of a typical year – but just remember that wildebeests and zebras don’t use the Internet...
There is no beginning or end to the migration but we’ll imagine it all starts with the onset of the “rainy season” (don’t be put off by this expression as the “green season”, as it is now often called, is a lovely time of year and usually nowhere near as wet or dismal as it sounds). The rains tend to begin around mid-November, when the big herds start to file into the south-eastern short-grass plains, around Naabi Hill, Lake Ndutu, the Gol Kopjes, Oldupai Gorge and all other parts of the short-grass plains.

Between late January and mid-March the wildebeest calving season takes place. At its peak about 80% of the pregnant females give birth within three weeks, collectively producing something like 8,000 babies each day. The large predators, of course, are on hand to take advantage of this glut.
Between mid-May and the month’s end, as the plains dry out, the whole menagerie, as if at the wave of a magic wand, streams off in columns which are sometimes 40 km. long, heading via the Moru Kopjes for the Western Corridor. On the way, the wildebeest rut takes place, for a period of about three weeks, from around mid-June to early July. Dr. Richard Estes, the greatest authority on the Serengeti wildebeest, has described the event as “unbelievably spectacular”. It is certainly chaotic, as something like 250,000 males strive to mate with as many of the 750,000-or-so females as they can

Between June and August the migrating animals drink from and eventually cross the Grumeti River, but for many it will be their last drink or their last river crossing. For here in the Grumeti are crocodiles that grow to over five metres in length and weigh more than three-quarters of a tonne. They have jaws so thickset and powerful that they can crush a wildebeest's head like a melon, then tear the body into bloody rags. Usually after yanking the victim into the water.

The great majority of wildebeest survive, to cross the Ikoma Controlled Area outside the park then pass through the Serengeti’s Northern Extension, crossing the next challenging river, the Mara, in July or August. Most but not all of the wildebeest and zebras also cross the Kenyan border a little way beyond, to remain in the Maasai Mara Reserve until about mid-October, when they begin the return journey. This takes them down the eastern boundary of the Northern Extension, in and out of the park, and eventually back to the short-grass plains. The 1000 km. trek – for those which make it - is complete.

Things to remember if you want to see the migration:
1) Decide which time of year you want to go to the Serengeti and choose a lodge or camp that will (hopefully!) put you within easy reach of the migration at that time. A few hints are given in the appropriate sector on hotels and lodges (Northern Circuit).
2) Don’t be put off by the term “rainy season”. It is one of the best times of year in which to see the migration.
3) Remember that you can almost always reach the migration from any lodge or camp within the Serengeti at almost any time, if you are prepared, in some cases, for a long drive.
4) Don’t make the mistake of thinking that if you don’t see the migration your trip to the Serengeti will be pointless. All parts of the Serengeti are interesting at all times, though the south-eastern plains, from about June to mid-November, are relatively empty (this doesn’t rule out the Lake Ndutu or Seronera localities, which have resident game even when the migration is absent).

*Note - the migration is a natural event and the timing varies month by month; year by year.
I hope the above information will help you realize that witnessing Migration will entirely depend on weather and their location at any given time can never be guaranteed as they can move approximately 100 miles overnight !!!.

Source: http://www.bushbuckltd.com