Tidal and sexual differences in the diet of Purple SandpipersCalidris maritimain Scotland

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Abstract
The analysis of the gut contents of Purple Sandpipers from eastern and northern Scotland showed that most of the diet at low tide consisted of molluscs, particularly littorinids (winkles), but also Mytilus edulis (mussels), Nucella lapillus (dog-whelks) and Rissoa interrupta. Crustaceans, annelids and algae were also eaten. At high tide Purple Sandpipers fed on the larvae, pupae and adults of Coelopa frigida (the kelp fly) when waves broke into banks of rotting algae along the high water mark. As the molluscs were swallowed whole and the shells crushed in the gizzard there may be limitations on the size of molluscs that can be eaten, below the size that can be swallowed. Purple Sandpipers with longer bills (females) took larger Mytilus edulis and littorinids than those with shorter bills (males). The evolution of sexual size dimorphism and resource partitioning by the sexes is discussed.