Foraging semipalmated sandpipers Calidris pusilla L. and their major prey Corophium volutator (Pallas) on the Starrs Point mudflat Minas Basin

Semipalmated Sandpipers, Calidris pusilla (L.) and their predominant prey, the amphipod Corophium volutator (Pallas) were studied on a macrotidal mudflat ( 6 km²) at Starrs Point (45°08' N, 64°22'w), Minas Basin during summer in 1978, 1979 and 1980. The sandpipers stop in this area and store energy prior to a presumed non-stop flight to wintering areas as distant as South America. Bird densities attained over 300/ha and numbers of C. volutator exceeded 50,000/m² locally. Aspects of the amphipod's biology examined include size, energy content, abundance, distribution and behaviour. Collected birds provided information on origins, sex ratio, flight range, fat content and diet. Their distribution, abundance, feeding behaviour and the effects of predation upon C. volutator were also studied. The effects of ingestion rate, prey size and time available for daylight feeding were considered in relation to energy intake, expenditure, fat deposition, and length of stay. Sandpipers fed where their amphipod prey were most abundant. Semi-diurnal tides appeared responsible for behavioural changes of both predation and prey and this factor and the differences in feeding conditions (e.g. daylength and prey availability) contributed greatly to the large cyclic variation in the amount of energy ingested. Fat seemed to be deposited most rapidly over spring tides. Evidence suggesting that the timing of migration is influenced by the same factors was also obtained.