Aims: The feeding ecology of Dunlin Calidris alpina wintering in southern European wetlands is poorly known. The aim of this paper is to describe the diet, prey selection, foraging habitat selection, and feeding behaviour of wintering Dunlins, and interpret this information in the light of the current knowledge on the feeding ecology of this species.
Location: The study was carried out in the sediment flats of the Tagus estuary, Portugal, which is the largest estuary in Iberia, and harbours large numbers of wintering waders.
Methods: Diet of Dunlin was investigated using dropping analysis. Foraging habitat selection was studied using bird counts and behavioural observations in sectors located on different types of sediment. The abundance of invertebrates in the sediment was sampled to evaluate prey availability and to interpret patterns of habitat selection by the birds.
Results: Scrobicularid bivalves and the gastropod Hydrobia ulvae were the most consumed prey items, followed by the isopod Cyathura carinata and insects. Prey species with higher biomass, such as Hediste diversicolor and Scrobicularid bivalves were preferred. The smallest and largest sizes of some important prey species were avoided. Dunlins showed a clear preference to forage in muddy, rather than sandy, sediments. Overall pecking rates were similar in all types of sediment, but deep probes were more frequent in softer mud.
Conclusions: Some of the staple preys of Dunlin in Tagus estuary are also abundantly consumed in northern latitudes. However, other prey species important in northern Europe are here replaced by similar and locally common species. In the Tagus estuary, Dunlin feed upon a broad spectrum of invertebrate species, but show clear patterns of selection of prey species and sizes. Dunlin prefer to forage on muddy substrates, probably because their main prey are more abundant and accessible here than in harder, sandier, substrates.
