Last updated at 21:27 22 November 2007

It is one of the great spectacles of the natural world and the largest mass movement of land animals on the planet.

This extraordinary picture, taken by award-winning wildlife photographer Steve Bloom, shows just a fraction of the 1.5 million majestic wildebeest which cross the Mara River in Kenya every year.

They are joined on this incredible journey by 500,000 gazelle and 200,000 zebra.

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Many barely visible through a dramatic cloud of desert dust, they stampede across the plains of the Serengeti National Park, six million wildebeest hooves churning up the verdant grassland until it resembles a World War I battlefield.

They are travelling South to reach the new grasslands of the Serengeti, leaving behind the now parched woodland of the Masai Mara National Park.

Once they arrive in February, they will spend the wet season here on their breeding ground.

Come next June they will undertake the journey north once more, to the now rejuvenated forests of Masai Mara.

It is one of nature's most remarkable cycles, replenishing the vegetation of Northern Africa. A 500km round trip, it is undoubtedly one of the natural world's most astonishing phenomena.

This is a path fraught with dangers. The waters of the Mara River are teeming with hungry crocodiles and the strong currents can claim as many as 3,000 wildebeests each year.

Add to this the lions, hyenas, leopards and jackals lying in wait on dry land, and the jostling mass of herbivores seems like a banquet in waiting. They are particularly vulnerable at night, when individual stragglers can be picked out, and the younger and weaker members of the herd are easily dragged down.

Overall, about 250,000 wildebeest die during each trip.

Although the wildebeest of the Serengeti are thought to have followed a migratory path since ancient times, it is only in recent years that this circular migration was necessary.

In the 19th century the population was ravaged by disease and declined to less than 200,000. However, after veterinary intervention in the early 1960s their numbers once more began to swell, reaching a staggering 1.4 million in a matter of years.

Forced to search for new supplies of grass and water to nourish their growing herd, the current migration route was established. It is a demanding cycle of life and death.

Of the 400,000 calves born in the Serengeti every year, only one in three will return from their first and most challenging migration.

Steve Bloom, who took the picture, has travelled the world capturing some of the animal world's breathtaking sights with his camera. But the sheer majestic beauty of the wildebeest migration is surely the one which brings us closest to nature.