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At the heart of the Serengeti ecosystem lies an ancient phenomenon that is the largest movement of wildlife on earth. In pursuit of food and water, over a million wildebeest and half a million zebra and antelope migrate north from the Serengeti to the adjoining Maasai Mara reserve in Kenya every year. We were there at the end of January, during the wet season. January brings "short rains" to the Serengeti; it usually rains briefly and not every day. We encountered the migratory herds in the south east of the Serengeti park and the adjacent Ngorongoro Conservation Area.
dry season arrives around June, the grasses are exhausted and the wildebeest
head to permanent water. Forming columns which stretch for miles, the
wildebeest are joined by other hoofed animals. Predators follow and
crocodiles wait hungrily in the rivers. Only those herbivores which can do without
surface water for long periods and live on
poor forage remain during the dry
season. Come November, when the grazing is finished in the north and the rains
in the south, the army of animals surges
back to the renewed pastures to mate and calve. Only through migration can the herds use the
widespread resources of the ecosystem and build up such huge numbers.
White bearded wildebeests are the most common large animal on the plains and the principals of the migration. These wildebeest live in denser concentrations than any other large mammal, except for humans. Wildebeest are known as gnus in southern Africa due to their gnu gnu sound. Click here to hear. (If this sound file does not work with your system, try this version instead.) Although the wildebeest looks (according to African legend it was assembled from spare parts) and sounds comical, it is superbly evolved for its migratory plains lifestyle.
Wildebeest are constantly on the move, always striving for the side with the greener grass. As the sea of grass provides little cover and young are easy pickings, wildebeest have evolved synchronized birthing: About 90 per cent of calves are born within a three week period. Predators cannot make much of a dent in the population of newborns with such a sudden glut of food. Wildebeest young can run minutes after they are born. Within three days, calves are strong enough to keep up with the herd.
Plains zebra and wildebeest often intermingle. They are complementary grazers, preferring different parts of the same grass. Zebra, with their superior vision and hearing, serve as an early warning system for the wildebeest. Given the choice, predators prefer wildebeest meat to zebra. So zebra are happy to offer the carnivores that choice.
To zebra, it's a migration.