Ardea
Official journal of the Netherlands Ornithologists' Union

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Goss-Custard J.D., West A.D., Caldow R.W.G. & Durell S.E.A. le V. dit (1996) An emperical optimality model to predict the intake rates of Oystercatchers Haematopus ostralegus feeding on Mussels Mytilus edulis. ARDEA 84 (A): 199-214
A foraging model is presented for Oystercatchers, Haematopus ostralegus, opening Mussels, Mytilus edulis, by stabbing or by hammering through the shell on the dorsal side. For birds of average foraging efficiency, the model predicts the 'interference-free intake rate' (IFIR), in mg ash-free dry mass (AFDM) consumed per 5 min, from the densities of each of five mussel length classes and from their ash-free dry mass. The model is based on simple foraging theory but is built from empirical equations derived from field work on 31 sites on four mussel beds. The thickness of the mussel shell on the dorsal side had so small an effect on model predictions for hammerers that it was excluded from the basic version of the model. Predictions were tested by comparison with observed values in 22 sites on four mussel beds that did not contribute data to the equations. Predictions matched the observed values well for intake rate and feeding rate (Mussels consumed per 5 min) and for the mean lengths and size-frequency distributions of the Mussels taken. The model can be used to explore how intake rate is affected by spatial and seasonal variations in the abundance and flesh-content of Mussels and to define the functional response of Oystercatchers.


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