In this study, we describe food availability and diet selection of the Red Knot Calidris canutus islandica wintering in three estuarine bays on the French Channel coast. We examined whether the distribution of birds is related to the density and availability of high quality prey. Results indicate strong seasonal and inter-annual variation in the abundance of birds and considerable variation in prey-item abundance and diet selection depending upon site. At Mont Saint-Michel Bay, the prey community was dominated by Baltic Tellins, Macoma balthica. As expected from their high meat-to-shell ratio, Macoma contributed more than 90% of the diet. Most of the cockles, Cerastoderma edule were too large and their quality too low to be preyed upon. Less than 100 km away, in Saint-Brieuc Bay, Red Knots mainly selected the Thin Tellin Tellina tenuis. Although Tellina are a lower quality prey than Macoma, they occurred at a high density and in some winters might explain why the number of Red Knots exceeds those at Mont Saint-Michel Bay. At Bay des Veys, Normandy, Red Knots were restricted to a small intertidal area and fed on Abra tenuis, Macoma balthica and Hydrobia ulvae.