Factors Controlling Within-Flock Feeding Densities in Three Species of Wading Bird

Data for 70 Oystercatcher flocks suggest that density within the feeding flock is correlated closely with the density of second year cockles (Cerastoderma edule). None of the variables measured correlated significantly with density within the 83 Curlew flocks observed. It is suggested that the densities of Mya arenaria and Arenicola marina may exert a controlling influence on the spacing behaviour of feeding Curlews. The within-flock feeding density of Dunlins was most closely related to total prey density but, for a given prey density, was significantly lower on mud than on sand. Further data on Dunlin behaviour show that the feeding tactics adopted by this species on mud were different from that used on a sand substrate. Possible explanations for these differences are outlined.