Polychlorinated biphenyls in oystercatchers (Haematopus ostralegus) from the oosterschelde (Dutch Delta area) and the Western Wadden Sea, that died from starvation during severe winter weather.

Wintering oystercatchers (Haematopus ostralegus), charadriid shorebirds that chiefly feed on intertidal bivalves, suffered mass mortality in The Netherlands during severe frosts in 1986 and 1987. PCBs were analysed in liver and (partially) brain lipids of 96 birds to examine the influence of age (three categories), sex and wintering area (the Oosterschelde estuary versus the westernmost Wadden Sea) on levels, and the risk of intoxication due to starvation. Victims had lost nearly 40% of their normal winter weight. PCB-structures were similar in all age/sex categories, and in both areas. Sex did not affect total PCB-concentrations. First-winter Wadden birds had lower levels than subadults and adults, but an age-difference was absent in the Oosterschelde birds. Some juvenile outliers possibly originated from polluted breeding areas. Individual variation was considerable in most categories. Relevant ecological factors are discussed. Although a dam has considerably reduced the direct transport of PCBs into the Oosterschelde since 1969, contamination of local birds was hardly lower than in Wadden winterers. Influx of riverine PCBs into the Oosterschelde from coastal water may have been underrated. Starvation increased liver concentrations by a factor of 35; factors for the brain were 56 for juveniles and approximately 120 for older birds. Considering published lethal levels for other species, it is doubtful if PCBs contributed to this winter mortality.