Reevaluation of patterns of mussel (Mytilus edulis) selection by European Oystercatchers (Haematopus ostralegus)

European Oystercatchers (Haematopus ostralegus) were highly selective towards mussels between 35 and 50 mm in length, and fewer than 5% of mussels taken were below 35 mm or above 50 mm. The oystercatchers selected ventrally thin-shelled mussels, especially if the length was more than 35 mm, regardless of whether they opened the right or left valve of the mussel. The oystercatchers also took mussels that had few barnacles on the ventral surface. Although brown-shelled mussels were rare in the population, oystercatchers showed a strong preference for them. Generally, oystercatchers consumed ventrally flat mussels, especially in the smaller length classes, particularly the most preferred size class, 30–45 mm. Ventral shell thickness and colour had independent effects on mussel selection. The other two variables, number of barnacles and shape of the ventral surface (flat or curved), apparently had no influence on selection on their own, only by way of their association with colour or thickness.