Feeding behaviour of wintering Shelduck on the Clyde Estuary

Abstract

The feeding distribution and routine of Shelduck Tadorna tadorna on the intertidal flats of the Clyde Estuary were studied during the winter of 1978-79. Flocks on two areas offering somewhat different food resources were selected for intensive observations. Invertebrates were exploited by 'dabbling', 'head-dipping' end less frequently by 'scything' and 'upending'. 'Mini-craters', the impressions formed as a result of 'dabbling' are described. A diphasic tidal rhythm of feeding was observed, with peak intensities occurring over the mid shore. Shelduck fed in a tight straight line on the fringe of the ebbing tide, predominantly by 'dabbling', ingesting available organisms in the upper 3 cm of sediment. They dispersed during low tide to roost and occasionally feed, whilst others departed to lower lying feeding grounds. During flow tide several hours after the tide had turned, Shelduck tended to converge on patches on the mid-shore. Possibly such clumping was a response to surface availability of Hydrobia ulvae, Corophium volutator and less patchy Nereis diversicolor.