The abundance and distribution of intertidal invertebrates, and an estimation of their selection by Shelduck

Abstract

A study was made to estimate prey selection by wintering Shelduck Tadorna tadorna foraging on the intertidal flats of the Clyde Estuary. This involved sampling from craters which had been formed by the dabbling feeding action of Shelduck. Assays of invertebrates from sediments which had passed through the bill and from undisturbed sediments showed there was general selection for invertebrates just greater than 2.0 mm long. Small worms, especially Tubifex costatus, constituted the patchiest and greatest biomass component available, and were assessed prevalent in the diet. Simple calculation showed broad agreement between an estimation for intake of Hydrobia ulvae and its known inclusion in stomach contents. There was no association between feeding intensity and abundance of any single prey species or with any particle size range. A negative relationship between durations of feeding and intervening movement was apparent, suggesting that continual exploitation of a patchy resource was accompanied by a reduction in travel times.