Not all Oystercatchers Haematopus ostralegus select the most profitable common ockles Cerastoderma edule: a difference between feeding methods.

We use an optimality model to describe prey choice by wintering Oystercatchers Haematopus ostralegus using different feeding methods . Birds fed on Common Cockles Cerastoderrrea edule, which they opened by either exclusively hammering or stabbing. The model includes probabilistic time costs associated with successful and unsuccessful prey handling, changes in the energy content 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 > 15mm throughout the winter. The decisions made by stabbers were consistent with this . Hammerers consumed cockles > 15mm during late winter, but during early winter, consumed more 0-15mm cockles than expected . This implies that selecting pro fitable prey entails an additional cost specific to hammerers . This cost could be the risk of bill damage. As a result, hanunerers should only select the most profitable cockles when the benefit of maximising energy intake is greatest . This is most likely during late winter.

Johnstone I. & K . Norris, Ardea 88(2) : 137-153