The ‘world’s largest mammal migration’ happens here every year. War means no one knows about it

From an aerial view, golden-brown specks cover the grass like ants. Zoom in and you’ll see horns, backs, legs moving – all in the same direction. Antelopes, hundreds of thousands of them, are crossing the savannas of South Sudan.

The central African country has been ravaged by war over the last few decades, making it unsafe for scientific research, and data on the movement of wildlife there has been limited. But a report published today estimates that South Sudan is home to the largest known migration of land mammals on Earth.

Five million white-eared kob, 300,000 tiang, 350,000 Mongalla gazelle and 160,000 Bohor reedbuck (all species of antelope) are thought to traverse the landscape each year, moving from the savannas in the south of the country towards the wetlands in the north and east.

The estimates come from a 2023 aerial survey of the land around the Boma and Badingilo national parks and Jonglei region, referred to as “the Great Nile Migration Landscape.” A plane flew over transects of land at a constant height above ground, sampling almost 4,000 square kilometers (1,500 square miles) of a 122,000-square-kilometer (47,000-square-mile) area, while an observer recorded what they saw, and a camera, fixed to the plane, took a photo every two seconds. The method is commonly used to assess the distribution of wild animals in large open spaces and was previously done in the region in the 2000s and the 1980s, during relatively peaceful intervals between periods of unrest.

South Sudan, a country in central Africa, has a varied landscape, from rainforests to lush savannas and swamplands fed by the Nile River (pictured). It is home to an array of wildlife, but the country’s long history of unrest has made it hard to carry out scientific research.     Marcus Westberg

The latest results have astounded scientists: while wildlife has decreased in many areas of the world due to human development and climate change, this data shows that the migration has not only survived years of war but expanded.

“If the numbers are right with these species, it looks like they’ve increased since 2007. It looks like they’ve increased since the 1980s even,” says Mike Fay, lead researcher and conservation director for African Parks in South Sudan. He cautions that the margins of error are large, but even at its lowest estimate of four million antelope, the figure dwarfs the roughly two million wildebeest that move across Tanzania’s Serengeti, in what has long been considered the world’s largest land mammal migration.

The distances covered also rival the world’s longest annual land migration. While routes vary between species, the survey found that some tiang covered more than 3,000 kilometers (1,864 miles) – putting them on a par with caribou in Canada’s Arctic.

Fay, who has been working on conservation projects in Africa for more than 40 years, admits his exposure to natural phenomena has been extensive. He’s seen countless elephants, lions, gorillas and other iconic animals. “It’s hard to impress me, right?” he says.

Yet, when he observed thousands upon thousands of antelope running across the landscape, even he was flabbergasted.

“How is it even possible that there can be this many wild animals?” he marvels. “It’s not so much a sentimental thing for me, it’s more about the biological and ecological capacity of this land to produce so much wildlife. It’s truly phenomenal.”

War and peace

The migration’s survival – and growth – is likely to be linked to the decades of instability in the country, says Fay. South Sudan gained independence from Sudan in 2011 after decades of civil war. Quickly after that it descended into its own civil war, which ended in 2018, although local violence continues. As a result, the human footprint has remained low – the United Nations lists it among the least developed countries in the world.

“Maybe that provided this opportunity where the animals were left alone for a period of 10 to 12 years, and that’s when they became much more numerous,” Fay speculates.

This idea is supported by data from GPS devices that were fixed onto around 125 antelopes, tracking their movements over the last year. While the sample is too small to make big assumptions, one thing is clear, says Fay: “These animals try to avoid humans as much as they can.” Their tracks form a pattern like a donut, he says, with the antelopes circling around human settlements.

In contrast, non-migratory animals that were unable to avoid human populations have not fared so well. The survey cites catastrophic declines in sedentary species such as giraffe, buffalo, zebra, hartebeest and waterbuck.

“There was a gigantic proliferation of guns in the country, and you had thousands and thousands of people living in the bush. They weren’t cultivating, so they were eating a lot of wildlife and feeding the troops with wildlife,” says Fay. While moving wildlife populations could head to remote hinterlands, sedentary species were easy targets. “Those species got hammered,” he adds.

However, the lack of development has meant that the natural ecosystem around the migration remains more or less intact. South Sudan often refers to itself as “the land of great abundance” and in many respects, it lives up to this, says Fay.

Despite being land-locked, South Sudan has vast freshwater resources, including Africa’s largest wetland, the Sudd, which is fed by the overflow of the White Nile. The name is derived from the Arabic word for barrier, and for centuries the area was deemed impenetrable – the Sudd marked the southern limit of the Roman Empire’s expansion into Africa. This remoteness has helped to protect the region’s biodiversity.

“On most places on Earth, major river floodplains have had levees built along them, or they’ve been overused and degraded,” says Fay. “Whereas here, the water comes out of the mountains, hits that gigantic floodplain and just fans out … The fact that you’ve got this enormous floodplain still functioning in this modern world is phenomenal.”

It is this unique floodplain that brought conservation biologist Steve Boyes to South Sudan to support African Parks in the survey. As part of his Great Spine of Africa expedition, in partnership with the Rolex Perpetual Planet Initiative, he wanted to document how the watersheds and rivers – what he calls “the lifelines of these landscapes” – were playing into the annual migration.

He explains that the region has experienced record-breaking floods in recent years, in part due to pollution from South Sudan’s capital Juba, as plastic and human waste enter the river that flows into the Sudd and block the waterways. This could threaten the wider ecosystem and wildlife populations.

“We’ve got water consuming the landscape, restricting where a migration can go,” he says. “We’ve got growing human settlements, creating a smaller corridor. Those dynamics – human development, encroachment, and the flooding of the White Nile – will become more of a problem for migration.”

“Often in these post-war wildernesses, peace becomes a serious threat to wildlife populations,” he adds.

Opportunity

Fay fears the same. Wildlife has thrived in the “no man’s land” enforced by the conflict, but now that the nation is in a period of relative calm, efforts to restore it are firing up. “Roads are being built, industrial activities are starting to happen, people’s mobility is increasing, the tribal boundaries are becoming diluted,” he says.

“As they erode, as transport infrastructure becomes possible, that’s when we’re going to see a massive collapse of these animals.” He explains that migratory species are particularly vulnerable to linear developments such as roads because a physical barrier can cut off their migration path, while also exposing them to hunting.

But development doesn’t have to be bad for wildlife, he argues. If looked after, the migration could bring a number of benefits – it could even be “an engine for development,” Fay says, pointing to Tanzania, where the Serengeti national park, home to a vast wildebeest migration, pulls in as many as 200,000 tourists each year.

Boyes notes there could also be opportunities to generate carbon revenue from the Sudd swamps or establish community-run conservancies that bring benefits to both nature and people.

But Fay warns that conservation is always hard, and it takes time. “If you’re going to build an economy around this migration, the lag time between the cost and the benefit is great,” he says. Mass tourism is still a long way off in a country that has the reputation for being one of the most dangerous in the world, and as it struggles with a fragile and stagnant economy and the ongoing conflict and crisis in neighboring Sudan, wildlife may pay the price.

“Liquidation of natural resources is the fastest way to make a buck,” he says. “For a country like South Sudan to forgo some aspect of development for something that might not produce tomorrow, that’s where the political will comes in, and the will of the people.”

Currently, political will does seem to be there. African Parks carried out the survey with the support of the South Sudan government and the results will be used to inform the country’s wildlife conservation strategy for the area.

At a press conference announcing the results of the survey, the country’s president, Salva Kiir Mayardit, said, “As South Sudan continues to develop we are committed to transforming the wildlife sector into a sustainable tourism industry. To activate this I call upon the security forces, particularly the Ministry of Wildlife and its partners to prioritize the training and equipping of wildlife rangers to combat poaching and trafficking of illegal wildlife products in protected areas.”

Fay believes funding will be key. “The nation has to decide, do we want to maintain this migration or not?” he says. If yes, it then needs to invest heavily in conservation and land management, to preserve these unique natural areas.

“We have a window of opportunity,” he says, “but it’s closing as we speak.”

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