Emaii just in:
I'm a graduate student of Beijing Normal University. I studied shorebirds in Tanshan coastal area of northern Bohai Bay during last three years. We found Eurasian Curlew, Grey Plover and Dunlin wintered there. It's very interesting because Eurasian Curlew and Grey Plover are more than 5% and 1% of the estimated the East Asian-Australiasian shorebird flyway population respectively. I know you did a great job of waterbird in northern Bohai Bay. Would you tell me if you ever found any wintering shorebirds in Bohai Bay especially these three species and any paper reported winering shorebirds in this area? Could you sent me a copy?
I've replied: Didn't do much on coast south of Beidaihe in winter; but at Beidaihe, seems all shorebirds were absent in winter (in 1980s, as earlier this century). I remember one March, with about zero shorebirds Beidaihe (maybe an early curlew), to Daqinghe [near Happy Island], and several hundred Dunlin, a few Saunders' Gulls and other birds on mudflats by the village. I guessed they were early migrants, but maybe some wintered.
Done report on autumn migration; could send you copy if you give me address. Shorebirds section is at: http://www.drmartinwilliams.com/beidaihe-birding/beidaihe-autumn-report-...
Seems other authors, from earlier, likewise found shorebirds were migrants, at least to Beidaihe area. So, my guess is that maybe you're seeing some results of global warming - my impression is that ne China relatively highly affected by this; Jesper Hornskov has emailed re ice not forming till later in autumn, birds inc egrets lingering longer. Guess you have looked at this: including at temperature changes, and reports about sea ice. Maybe as sea ice boundary moves north, so too are shorebirds that can tolerate the cold, spreading to use mudflats that till recently were frozen, so impossible places for most shorebirds.