Feeding behavior and effect of prey availability on Sanderling Calidris alba distribution on Kujukuri Beach

Abstract

The distribution of Sanderling Calidris alba, and inter-tidal infaunal biomass was monitored over an annual cycle. In addition, the feeding behavior and fecal contents of Sanderling were studied in order to examine the relationship between the seasonal distribution of Sanderling and prey availability at Kujukuri Beach, Chiba Prefecture. Sanderling were observed on the beach from August through winter to May with an estimated total number of ca. 600 birds consistently being recorded from September to May. The numbers were supplemented by passage migrants with peaks in August, late January/early February and April. Direct observation, prey availability and fecal evidence indicated that Sanderling fed mainly on the surf clam Donax (Chion) semigranosus, the isopod Excirolana chiltoni and the mysid Archaeomysis vulgaris as well as insects. During winter (December to February) when the densities of E. chiltoni and A. vulgaris markedly decreased, Sanderling distribution was positively correlated (P<0.01) with the distribution of D. semigranosus, which formed its main prey during this period. Sanderling were observed to direct their attacks on D. semigranosus at the surf clam's muscular foot and the shell part was subsequently discarded. We conclude that Kujukuri Beach is important both as an over-wintering site and as a temporary stopover site for migrant Sanderling and that over-wintering Sanderling respond to the seasonal variation in the abundance of their main prey.