Not all oystercatchers Haematopus ostralegus select the most profitable common cockles Cerastoderma edule: A difference between feeding methods

We use an optimality model to describe prey choice by wintering Oystercatch ers Haematopus ostralegus using different feeding methods. Birds fed on Com mon Cockles Cerastoderma edule, which they opened by either exclusively ham mering or stabbing. The model includes probabilistic time costs associated with successful and unsuccessful prey handling, changes in the energy conte nt of prey, factors which affect prey availability and assumes that energy intake was maximised. Prey profitability increased with size for hammerers and stabbers. The model predicted that both should only consume cockles > 1 5mm throughout the winter. The decisions made by stabbers were consistent w ith this. Hammerers consumed cockles > 15mm during late winter, but during early winter, consumed more 0-15mm cockles than expected. This implies that selecting profitable prey entails an additional cost specific to hammerers . This cost could be the risk of bill damage. As a result, hammerers should only select the most profitable cockles when the benefit of maximising ene rgy intake is greatest. This is most likely during late winter.