At the mouth of the Yalu River, where China meets North Korea on a brown estuary the size of a small country, the tide drops two and a half kilometres in six hours. What it exposes, twice a day, is a flat of fine grey silt rich in tube-worms, bivalves, and small crustaceans.
For several million shorebirds, the Yellow Sea mudflats are not optional. The birds that breed in Arctic Russia and Alaska and winter in Australasia depend on these flats as a single, irreplaceable refuelling station on the long northward migration. There is no plausible alternative anywhere along the route.
Between 1985 and 2010, roughly sixty-five percent of the Yellow Sea's intertidal mudflats were lost to reclamation. Most of the reclaimed land became industrial parks, salt pans, aquaculture ponds, or residential development. The pace of loss in some provinces reached two percent per year.
The biological consequences were immediate and severe. Populations of several flagship shorebird species collapsed. The spoon-billed sandpiper, a small sandpiper with a distinctive spatulate bill that breeds only on the Russian Far East coast and stages in the Yellow Sea, declined to fewer than three hundred breeding pairs by the mid-2010s.
The great knot, a robust mid-sized shorebird that winters in northern Australia, lost an estimated fifty-eight percent of its population between 1993 and 2017. The bar-tailed godwit subspecies menzbieri, which uses the Yellow Sea exclusively on northward migration, declined by similar margins.
Inara Khan, Roost's Habitat editor, visited the Yancheng coastal wetlands in Jiangsu Province in April 2026 with a small group of researchers from the Beijing Forestry University. Yancheng holds one of the last large stretches of unreclaimed Yellow Sea mudflat, protected since 2019 as part of a UNESCO World Heritage inscription.
The inscription, which covers a string of sites along the Yellow Sea coast in Jiangsu, Liaoning, and elsewhere, was the result of nearly a decade of international advocacy. It was opposed by some provincial development interests and supported by a coalition of Chinese, Korean, Japanese, Australian, and New Zealand researchers.
It does not, by itself, stop reclamation. What it does is raise the political cost, and create a framework for monitoring, that did not previously exist.
On the morning Khan visited, the tide was falling at Tiaozini, a key site within the Yancheng inscription. As the mud emerged, the birds arrived in waves. Great knots, bar-tailed godwits, red knots, Terek sandpipers, broad-billed sandpipers, and, in a small cluster on the edge of the larger flocks, perhaps thirty spoon-billed sandpipers.
The spoon-bills feed by sweeping their broad-tipped bills side to side through shallow water and soft mud. They are easy to pick out at close range and almost impossible to distinguish from red-necked stints at any distance. The thirty birds at Tiaozini represented perhaps ten percent of the world's remaining adult population.
Lei Cao, an ornithologist at the Chinese Academy of Sciences, has led counts at Tiaozini and the surrounding sites since 2014. She has watched the spoon-bill population stabilize, slowly, after the addition of new protected areas in Russia, the Yellow Sea, and southeast Asia. The trajectory, she said cautiously, is no longer one-way down.
The threats have shifted but not disappeared. Direct reclamation has slowed substantially in China since 2018, when the central government issued a moratorium on most new coastal reclamation projects. The moratorium does not apply to North Korea, where reclamation continues, and where access for monitoring is extremely limited.
Aquaculture expansion has, in some areas, replaced direct reclamation as the principal pressure. Shrimp and shellfish ponds, often built on former mudflat, do not always destroy the habitat outright but can fragment it and reduce its biological productivity.
Spartina, an invasive cordgrass introduced to China in the late 1970s for shoreline stabilization, has colonized many of the remaining mudflats and is now spreading more rapidly than it can be controlled. Where Spartina takes hold, the birds disappear within a few seasons.
What has improved, measurably, is monitoring. The flyway is now covered by an integrated network of count sites from Australia and New Zealand through southeast Asia to the breeding grounds in Arctic Russia. Coordinated counts conducted twice annually generate population estimates within a few percent of true values.
Pell Murphy, in his eBird tracking work, notes that the volunteer count effort on the flyway has grown roughly fivefold in the last decade. The data is now sufficient to detect population trends within five years rather than fifteen.
What it cannot do is replace the lost habitat. The mudflats that were reclaimed in the 1990s and 2000s are not coming back. The birds that depended on them are not coming back either, in any meaningful timeframe.
On her last afternoon at Yancheng, Khan walked along a dyke road built atop a 2007 reclamation. To the seaward side, the mudflats stretched to the horizon, full of birds. To the landward side, a complex of shrimp ponds, salt evaporators, and partially built wind turbine foundations stretched equally far inland.
Twenty years ago, the landward side had been mudflat too. The birds had used it. Now they used a narrower band, and the band was holding, for the moment, behind a fragile combination of national policy, international scrutiny, and the patience of a few researchers who have refused to give up on a flyway that came close to collapse.
By evening, the tide was rising. The birds lifted in long ribbons, climbing into the wind and turning south down the coast to roost. Khan watched them go. The light fell behind the wind turbines on the inland horizon. The mudflats vanished under brown water, and the great knots, which had flown six thousand kilometres to feed here, settled for the night on what was left.
