Patch Selection by Dunlin on a Heterogeneous Mudflat

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Abstract
The foraging behaviour of Dunlin Calidris alpina was studied on a mudflat in eastern England [UK]. The distribution of birds was related to the different substrates present on the site. Mud samples were collected to compare the density and biomass of prey and physical properties of the sediment. The invertebrate fauna was dominated by oligochaetes, but the distribution of Dunlin on the site was not directly related to oligochaete density. Most Dunlin fed using tactile stimuli to locate prey in the softest mud. The softer mud was more easily penetrated by a Dunlin''s bill, hence the prey were more accessible, so the availability of vulnerable items was greater. A few birds detected prey by sight and these concentrated their feeding in regions where the density of large polychaetes in the sediment was greatest. Patch selection for areas of higher prey accessibility and (possibly) lower foraging costs could be achieved by a simple ''rule of thumb'' of selecting wet substrates.