DIFFERENCES IN POPULATION-STRUCTURE BETWEEN 2 OYSTERCATCHER HAEMATOPUS-OSTRALEGUS ROOSTS ON THE BURRY INLET, SOUTH WALES

Comparison is made between Oystercatchers caught by cannon netting at two roost sites on the Burry Inlet in the winter months of 1990 and 19 91. Proportionally more adult birds were caught at a large roost at Wh iteford Point, and more juveniles at a smaller roost at Llanelli North Dock. Adults caught at Whiteford Point were also less likely to be su ffering from deformities and more likely to be males. These findings a re contrasted with previous work on the Wadden Sea, where Oystercatche rs caught at large roosts containing more adult birds and fewer deform ed birds were more likely to be oo. Mechanisms for assortive roosting are discussed. It is suggested that the population structures of the d ifferent Oystercatcher roosts on the Burry reflect the feeding prefere nces of the birds present, but that feeding preferences may also be in fluenced by a bird's social status, or dominance.