In an area you've probably never heard of, the largest movement of land mammals on the planet is under way.

Each year millions of white-eared kob, Mongalla gazelle, tiang and Bohor reedbuck migrate across the Boma Badingilo Jonglei Landscape in South Sudan. A survey just completed by African Parks and the Sudanese Wildlife Ministry counted about six million antelope.

The findings confirm a remarkable and unmatched wildlife phenomenon across a landscape of immense ecological importance which is largely unknown to the rest of the world.

The survey covered 122,774km2, encompassing the entire known range of the four main migratory antelope species in the Great Nile Migration. Data from 251 tracking collars on large mammals was also integrated, providing a wide understanding of the region's ecological dynamics which includes parts of South Sudan and Ethiopia.

Announcing the survey results, South Sudan President Salva Kiir Mayardit said it confirmed that the country remained rich in biodiversity with some of Africa's most beautiful animals.

"The results of this survey are nothing short of staggering," said Peter Fearnhead, CEO of African Parks.

"The astonishing scale of the migration is only equalled by the responsibility to ensure that it survives into the future in an extremely complex landscape."

War and commercial poaching have been an ongoing threat to the migration.

"This wildlife and larger ecosystem...