Foraging patterns and diet composition of breeding Pied avocets (Recurvirostra avosetta) in the German Wadden Sea

Abstract

Pied avocets (Recurvirostra avosetta) breeding in the Wadden Sea typically forage in shallow water, using their characteristic upward-curved bill to feed on macrozooplankton in the water column and prey items in the uppermost centimetre of the sediment. Former studies on prey choice based on droppings and visual observations of feeding behaviour suggested that ragworms were the main prey items of avocets. The present study combined different methods to assess the foraging ecology of breeding avocets in the eastern Wadden Sea. Important foraging grounds were identified using GPS telemetry. Diet was analysed from droppings and stable isotope signatures of whole blood samples from breeding avocets at two different colonies in April–June 2014 and 2015. Analysis of droppings confirmed the former results, but stable isotope analysis suggested that marine fish comprised the highest proportion of the avocet diet by mass. Telemetry data indicated that intertidal channels close to the breeding areas were used as the main foraging grounds. Avocets performed short foraging trips (maximum distance: 0.3–5.9 km) mainly during the daytime. Logger data and diet analysis thus implied the existence of high fish densities in intertidal channels, underlining the importance of this saltmarsh habitat as foraging areas for breeding avocets.