MEININGER PL, BLOMERT A-M & MARTEIJN ELC (1991) Mortality of waterbirds in the Delta area, Sw. Netherlands during the three cold winters of 1985, 1986 and 1987. LIMOSA 64 (3): 89-102.

As a result of severe weather during the winters of 1985, 1986 and 1987 (figures 1 and 4), notable mortality occurred among waterbirds wintering in the Delta area, SW. Netherlands (figure 2). Total numbers of victims found were 4712, 7669 and 4570 respectively (table 1). Especially Oystercatcher (9811 birds found dead, 58% of all birds found), Shelduck (1114, 7%) and Redshank (702, 5%) were heavily afflicted. Redshank was the most vulnerable wader species whereas Dunlin and Bar-tailed Godwit were hardly affected. Mortality among Oystercatchers was relatively low in 1985, but considerably larger in 1986 and 1987 (figures 6a, 6b and 6c). Mortality among non-wader species (excluding Shelduck) was small: on average 1.2, 1.6 and 0.4 % of the numbers counted (table 3). In all wader species except Knot, the proportion of juvenile birds among the victims was larger than in the populations present, as derived from captures (figure 7). The differences between wintering strategies of various wader (sub)species are discussed. Since smaller birds have higher energy requirements to maintain their body temperature than larger birds, it is assumed that it is more risky for small birds to winter in northern areas. Indeed, small (sub)species generally winter in larger numbers farther south than large (sub)species (figure 8). In all three winters the relative and absolute mortality in the Oosterschelde was higher than in the adjacent Westerschelde (figure 10). Due to the construction of a storm-surge barrier and two secondary dams, the tidal amplitude in the Oosterschelde was reduced from an original 3.7 m to 3.2 m in the winter of 1986, and to 2.4 m in the winter of 1987 (figure 3). This resulted in: 1) a reduction of intertidal area of 4 and 12 % respectively; 2) an increased formation of ice due to an increased residence time of the water. The greater part of cockle and mussel beds, the most important feeding areas of Oystercatchers, are situated in the lowest sections of intertidal zones. Due to reduction of tidal amplitude, these sections were exposed either during a shorter period of time, or not at all. This, in combination with increased formation of ice, is the major cause of the large numbers of (adult) Oystercatchers among the victims in 1986 and 1987. The tidal reduction seems to have had little or no effect on mortality in other species.

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