Wintering Oystercatchers in The Netherlands are concentrated in the Wadden Sea (c. 200 000), with substantial numbers in the Delta area (c. 90 000). Only 1% of the total wintering population is normally found along the North Sea coast. Cold-rushes under severe winter conditions lead to a reduction of wintering numbers in the Wadden Sea, and to increases ir,the Delta and along the North Sea coast. The mortality of wintering Oystercatchers in The Netherlands was studied on the basis of beached bird surveys along the coast of the North Sea and the Wadden Sea between 1969 and 1996. On the whole, the pattern corresponded well to annual mortality estimates from population studies on the Wadden Sea islands of Schiermonnikoog and Texel. Peak numbers of dead Oystercatchers were found in most severe winters, but also in some moderate winters such as in 1976 and 1991. In mild winters, rather small numbers of dead Oystercatchers were recorded. For 1986-1996, annual mortality along the coast ranged from a c. 500 in the mild winters of 1989 to c. 10 000 individuals in 1987 and 1996. Multiple regression analysis of the number of dead Oystercatchers in winter 1975-1996 on the number of cold days and the biomass of benthic prey revealed an explained variance of 66% (n = 21). Both the number of cold days and prey biomass had a significant effect. The results explained the relatively high mortality among Oystercatchers in the moderate winters of 1976 and 1991 (very low food stock), and the low mortality in the severe winter of 1982 (large food stock). The extremely high mortality in 1987 was due to a combination of low food stock and severe weather. The depletion of Cockles and Mussels in the Wadden Sea in the early 1990s, due to a combination of overfishing and failing reproduction, triggered a southward mass movement of Oystercatchers and substantial mortality in the Delta area in the winter of 1990-1991. The absence of a peak in the mortality among adult breeders in the population studies for that particular winter is the major ...