Red Knots (<i>Calidris canutus piersmai</i> and <i>C. c. rogersi</i>) depend on a small threatened staging area in Bohai Bay, China

We monitored numbers of Red Knots (Calidris canutus) staging in Bohai Bay, China (39°02'N, 118°15'E) on northward migration. Knots were identified to subspecies, and we systematically searched for colour-banded birds from the non-breeding grounds. We modelled migratory turnover, and revised estimates of flyway population using recently published counts from the non-breeding grounds. Two Russian-breeding subspecies occurred at our study site: C. c. rogersi (migrating to Chukotka), and C. c. piersmai (migrating to the New Siberian Islands); they co-occur on non-breeding grounds in Australia and New Zealand, but differ markedly in timing of migration. We conservatively estimate that our study site, comprising only 20 km of coastline, was used by over 45% of the combined world population of adult C. c. rogersi and C. c. piersmai—a conclusion supported by the independent data on frequency of resighting of colour-banded birds from north-western Australia and New Zealand. Much of this vital staging area is now being destroyed through construction of the Caofedian Industrial Zone and more westerly developments, which comprise only some of the many tidal flat ‘reclamation’ projects in the region. Preservation of the remaining tidal flats of Bohai Bay is essential to the conservation of Red Knots in the East Asian-Australasian Flyway.