1Every year, over a million wildebeest travel across the plains of East Africa.
2They follow the seasonal rains in an endless search for fresh green grass.
3The herds move together in long lines that stretch as far as the eye can see.
4Zebras and gazelles often join them on this long and dangerous journey.
5The hardest moment comes when the animals must cross the great Mara River.
6Crocodiles wait beneath the muddy water, ready to attack the weaker animals.
7Many wildebeest are too frightened to enter the river, so they wait for hours.
8Finally, one brave animal jumps in, and thousands of others follow behind it.
9On the other side, lions and hyenas watch the tired survivors carefully.
10Thousands of calves are born during the journey, and they must walk immediately.
11Scientists believe the herds can smell the rain from many kilometres away.
12This great migration is one of the most amazing natural events on Earth.