The Food beneath the Flock

Along Donggang’s coast, within Dandong, the Yalu estuary wetland includes tidal flats and shallow sea. Falling water exposes a feeding surface; rising water covers it again. The birds’ opportunity to use the mud is therefore governed by the tide as well as by the season. Feeding places and high-water resting places are complementary parts of the habitat.

This shore belongs to the East Asian–Australasian Flyway, the broad migration system connecting northern breeding grounds with non-breeding areas farther south. A stopover is active preparation for another flight. The mud matters because it can provide the energy needed to continue.

Research at Yalu Jiang during northward migration in 2011 and 2012 found that a small bivalve, Potamocorbula laevis, was important to several shorebird species. Great knots and red knots ate it, as did bar-tailed godwits, whose diet was broader. The birds were not simply taking any object that moved in the mud.

The study found differences in handling. Godwits and knots generally swallowed the shellfish whole, while Eurasian oystercatchers opened them and took the flesh. Shell size and the proportion of flesh to shell therefore mattered differently to different birds. An apparently uniform feeding flat contained choices about energy and the work of obtaining it.

A later study, published in 2018, followed food resources between 2011 and 2016 and documented a severe decline in the same bivalve. Bird use of the area did not fall uniformly in response. The authors interpreted the continued presence of many birds as evidence that alternatives might be scarce, rather than proof that food conditions remained good.

That result complicates a reassuring image of a crowded shore. Birds may continue to use a place because it occupies an essential position in their journey. During the study period, continued bird use therefore coexisted with a deteriorating food supply. The researchers’ comparison links habitat quality to the availability of other places along the migration route.

The 2024 extension of UNESCO’s Migratory Bird Sanctuaries along the Coast of Yellow Sea-Bohai Gulf of China included the Yalu estuary region. The property’s maps identify Dayang River and Erdaogou as components, each with its own boundary. World Heritage status belongs to those designated areas within a larger coastal landscape.

The serial property recognizes a network, much as migration depends on a sequence of usable places. At this end of the Yellow Sea, the link between distant journeys and local mud is unusually direct. A tiny shellfish, its feeding bird and the next stage of a flight are parts of the same system.