Wetenschappelijk artikelWesthoek saltmarsh – important staging site for Curlew Sandpiper (Calidris ferruginea) in the Dutch Wadden Sea

The Curlew Sandpiper Calidris ferruginea is a scarce species in the Dutch Wadden Sea, with short migration peaks during spring (May) and autumn (July–September). Due to these short peaks, the regular monthly counts of waders on high tide roosts may miss the peak numbers. To get a better estimate of the numbers of staging Curlew Sandpipers during autumn migration, we conducted weekly counts along an 11-km stretch of the Frisian Wadden coast, from Koehool to Zwarte Haan, during July 2001–September 2024. This stretch encompasses the two largest roosts of the species in the Dutch Wadden Sea, the salt marshes of Westhoek and Zwarte Haan. The annual maximum number during the first peak of autumn migration (from the end of July to early August) was 2,110–9,142 birds. Maximum numbers during the second peak (late August to mid-September) were usually lower than in the first peak (740–4,590). Many juveniles were recorded in some years, suggesting good breeding success. No juveniles were observed in July and early August, but they constituted 30–90% of birds mid-August to mid-September. Annual patterns in peaks from weekly counts differed from those in standard monthly counts, because the latter often missed the brief peak in migration. The high tide roost near Westhoek has become an important staging site for Curlew Sandpipers in both the Dutch Wadden Sea and the international Wadden Sea. High and increased densities of Mud Shrimps Corophium volutator could be a reason for its attractiveness.