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Westhoek Saltmarsh Held Up to 9,142 Curlew Sandpipers During Autumn Migration

Curlew sandpiper on a coastal mudflat
Research · Ecology

A 2026 study in Wader Study identifies the Westhoek saltmarsh as a major autumn staging site for the curlew sandpiper (Calidris ferruginea) in the Dutch Wadden Sea. Researchers analysed a weekly count series spanning 2001–2024 along an 11-km section of the Frisian Wadden coast between Koehool and Zwarte Haan, including the two largest local high-tide roosts at Westhoek and Zwarte Haan.

The counts showed two distinct autumn migration peaks. Annual maxima during the first peak, from late July to early August, ranged from 2,110 to 9,142 birds. The second peak, from late August to mid-September, was usually smaller, with maxima of 740–4,590 birds. No juveniles were recorded in July or early August, whereas juveniles made up 30–90% of birds from mid-August to mid-September in some years, reflecting the later passage of young birds. High juvenile proportions in some years also suggested relatively good breeding success on the Arctic breeding grounds.

Monthly counts can miss short migration peaks

The weekly surveys also showed how easily the short migration peaks can be missed by standard monthly high-tide counts. Dedicated counts at Westhoek were often higher than the monthly figures for the wider Frisian or Dutch Wadden Sea, in some comparisons by a factor of two and occasionally up to ten. The researchers attribute much of this discrepancy to timing: the main peaks occurred around the transitions between July and August and between August and September, while standard counts were generally made around the middle of each month.

Using a flyway population estimate of 300,000–400,000 birds and an average seasonal maximum of about 3,800 at Westhoek in 2016–2020, the authors estimate that roughly 1% of the flyway population used the saltmarsh. This was the largest recorded concentration in the Dutch Wadden Sea. They suggest that increasing densities of mud shrimp (Corophium volutator) on the silting mudflats may help explain the site’s attraction, although the local diet of curlew sandpipers has not yet been investigated.

Sources and image credit

  1. Kleefstra, R., & Schekkerman, H. (2026). Westhoek saltmarsh – important staging site for Curlew Sandpiper Calidris ferruginea in the Dutch Wadden Sea. Wader Study, 133(1), 6–11. https://doi.org/10.18194/ws.00392Primary research paper published 1 April 2026. Weekly counts along an 11-km section of the Frisian Wadden coast documented two brief autumn migration peaks, annual maxima of 2,110–9,142 birds in the first peak, and Westhoek as the largest recorded Curlew Sandpiper concentration in the Dutch Wadden Sea.

Image: TRinaud / Wikimedia Commons — curlew sandpiper photographed at Baie de l'Aiguillon, France, on 10 September 2023; representative species image, not a bird from the Westhoek study. · CC BY 4.0 · Source

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