Conservationists say they have discovered one of the largest migrations of land mammals on Earth in southern Sudan.
The Wildlife Conservation Society (WCS) said it found 1.3m migratory animals, despite fears of damage to numbers after a civil war in the region.
The US-based group also found an 80km-long (50 miles) and 50km-wide (31 miles) column of migrating antelopes.
"I have never seen wildlife in such numbers," said the WCS's Michael Fay.
"This could represent the biggest migration of large mammals on Earth," bigger even than the mass migrations of the Serengeti, he said.
The last survey of southern Sudan was conducted in 1982, a year before the decades-long civil war erupted in the region.
The WCS feared that the conflict, which ended in 2005, had taken its toll on the area's wildlife, as other conflicts did in parts of Mozambique and Angola.
But in their survey, field scientists said they found an estimated 800,000 white-eared kob (a medium-sized antelope), 250,000 Mongalla gazelles, 160,000 tiang and 13,000 reedbuck.
However, there has been a dramatic decline in the number of other animals, including elephants and zebras, and in some areas, buffalo.
The WCS said oil development along migration corridors and poaching were among the threats to wildlife in the region.
Plans are being formed to create an international conservation mission for south Sudan, part of which would involve retraining former rebel fighters to work as wildlife wardens.