Why Afro-Siberian Red Knots Calidris canutus canutus have stopped staging in the western Dutch Wadden Sea during southward migration

• Published in: Ardea
• Main Authors: Kraan, Casper, van Gils, Jan A., Spaans, Bernard, Dekinga, Anne, Piersma, Theunis
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2010
• Subjects: connectivity; East-Atlantic Flyway; foraging; habitat suitability; macrozoobenthos; migration; molluscivore shorebirds; predicted intake rate; AFFECTS FORAGING DECISIONS; COST-BENEFIT-ANALYSIS; INTERTIDAL FLATS; PATCH-CHOICE; ORGAN SIZE; FOOD; SHOREBIRD; BEHAVIOR; WADERS; LENGTH; Calidris canutus; Taimyr
• Online Access: https://hdl.handle.net/11370/79cf5e84-62ff-456d-8fc3-2174969cd1b9; https://research.rug.nl/en/publications/79cf5e84-62ff-456d-8fc3-2174969cd1b9; https://doi.org/10.5253/078.098.0204; https://pure.rug.nl/ws/files/2614121/2010ArdeaKraan.pdf

Afro-Siberian Red Knots Calidris canutus canutus use the western Dutch Wadden Sea as a refuelling area during southward migration from Taimyr to West Africa. Here we document the decline of their food stocks in this area, based on a yearly large-scale benthic mapping effort, from 1996 to 2005. For each benthic sampling position, intake rate (mg/s, ash-free dry mass) was predicted by an optimal diet model based on digestive rate maximization. Over the ten years, when accounting for a threshold value to meet energetic fuelling demands, subspecies canutus lost 86% of its suitable foraging area. Over this period, the proportion of probable canutus in mist-net catches in July-August declined relative to overwintering islandica Knots. This suggests that canutus dropped even more in numbers than islandica, for which we showed earlier a food-explained decline in numbers. We discuss the possible causality between a decline in the quality of intertidal mudflats in the Dutch Wadden Sea and population declines of Knots in the West-African wintering quarters.