Great wildebeest migration at Mara River, Kenya

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The race for life. Great wildebeest migration at Mara River, Kenya

They say the grass is always greener on the other side, and no one takes that more literally than the wildebeests of the Serengeti in Tanzania. Every July, roughly 2 million of these determined grazers, along with zebras and other herbivores, set off on a journey north to the Masai Mara in Kenya in search of lush pastures and fresh water. The great migration, considered one of the seven wonders of the natural world, is a safari spectacle where survival is the prize.

One of the most dramatic moments of the migration is the crossing of the Mara River at the border between Tanzania and Kenya. Thousands of wildebeests gather at the riverbank, aware that danger lurks beneath the surface—crocodiles—not to mention the lions and leopards that patrol the banks. When the first wildebeest takes the plunge, it's a wild rush as the rest of the herd follows, creating a chaotic scene. Some make it across, while others become part of the food chain. As October rolls around and the rains return to the Serengeti, the herds begin their journey back south, completing the cycle once again.