The timing of the migration
The exact timing of the migration varies each year and the triggers that drive the herds from the Serengeti’s short grass plains are still poorly understood. The diminishing availability of water and grazing at the onset of the dry season are clearly primary factors, but other factors are also thought to come into play. Some researchers have argued that rising salinity levels in the lakes and rivers of the volcanic plains at the onset of the dry season reach a precise and predictable level at which point the herbivores will start to move. The scattered herds gather into columns up to 25 miles (40 km) long to start on their journey westwards and northwards. Whatever the cause, the variations in timing make it difficult for visitors to plan their trip ahead of time to ‘catch the migration’ at any particular safari destination. Our migration safaris in Tanzania provide maximum flexibility to our guests, by providing mobile camping safaris that travel to the migrating herds.

The Serengeti eco-System
The Serengeti eco-System encompasses Tanzania’s Serengeti National Park, the Ngorongoro Conservation Area, the controlled areas to the north of the Grumeti River, the Masai Mara National Reserve in Kenya and the wildlife dispersal areas in the vicinity of the Mara. This vast unfenced eco-system spans across the political border between Kenya and Tanzania to allow the migrating herds free movement to follow their migratory instincts. It is a region of grass and woodland extending in an irregular pattern approximately 200 miles north-south and 200 miles east-west (320km x 320km).

This ecological system supports an incredible 1.6 million herbivores and thousands of predators. Approximately 1.2 million of the herbivores participate in the Great Migration. Most predators are territorial and do not migrate, but hunt the passing parade of wildebeest, zebra and gazelle as they pass through their territories.

The grazing succession
It is remarkable that such vast numbers of herbivores are able to mutually survive off the limited grassland resources of the Serengeti eco-system. The secret lies in the balance and mutual dependency of the grazing habits and preferences known as the grazing succession. The migration at most times is led by the Burchell’s Zebra who feed off the taller grasses, making it easier for the wildebeest to get to the shorter grass below. The remaining short grass left by the wildebeest has then been exposed for grazing by the Grant and Thompson Gazelle (‘Tommies’) that trail last in this great wildlife procession.

The wildebeests’ cycle of life
Life begins for a wildebeest calf somewhere on the volcanic short grass plains of the south eastern Serengeti or Ngorongoro Conservation Area. In a miracle of nature, hundreds of thousands of pregnant wildebeest will drop their calves within a 2-3 week timeframe, usually during February. The new born calves can stand within 7 minutes of birth, and are able to keep up with the herds within as little as two days. The newborn calves immediately attract predators, especially hyenas, cheetahs and African wild (painted) dogs. Only the cheetahs and wild dogs are able to easily run down the older calves, leaving the hyenas to pursue the new born. The result of the prolific birthing over such a short timeframe is one of survival. Most calves survive the vulnerable two days following birth, having vastly outnumbered the available predators.

Mating between wildebeest takes place generally around May and June, as the herds head into the woodland areas to the west and north, en route to the Masai Mara National Reserve. Bulls defend cramped territories, noisily rounding up passing cows, evicting other bachelor males and butting heads with territorial neighbors. The bulls attempt to breed with as many females as possible before the females move on through their territories. Wildebeest pregnancy lasts 8½ months.

An estimated 3,000 lions, 7,000 hyenas and countless other predators will exact a heavy toll on the wildebeest herds as they migrate along their journey through life. It is however a shortage of grazing and water during the dry season and the harsh environment that will exact the heaviest toll.