Ardea
Official journal of the Netherlands Ornithologists' Union

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Wanink J.H. & Zwarts L. (1996) Can food specialization by individual Oystercatchers Haematopus ostralegus be explained by differences in prey specific handling efficiencies? ARDEA 84 (A): 177-198
Three individually-tested adult Oystercatchers took different proportions of shallow-buried bivalves Mya arenaria and Scrobicularia plana from a mixture on offer in an experimental situation. Two birds, taking mainly or exclusively Scrobicularia, selected the species as predicted by a random search model based on encounter rate. The third bird actively selected for the less abundant Mya. All birds showed size selection within the prey species. Diet composition was correlated with the efficiency of the birds in handling the prey items. Optimal foraging theory adequately explained the observed prey species- and size selection by the birds. A short-term learning effect was found in two of the Oystercatchers. These birds managed to reduce their handling time during the course of the experiments, mainly by cutting the flesh loose from the shell faster. Cutting was always the most time-consuming component of prey handling but relatively more when a bird took the less preferred prey species. By rapidly improving their cutting technique for a specific prey, the birds increased their profitability. This adaptive behaviour contradicts the view of the Oystercatcher as a conservative specialist, which has problems when alternative prey should be taken in times of food shortage, although under natural conditions prey switching is hampered by morphological constraints.


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