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Foraging and size selection of mussels by the tufted duck, Aythya fuligula
Draulans, D. (1982). Foraging and size selection of mussels by the tufted duck, Aythya fuligula. J. Anim. Ecol. 51: 943-956. https://dx.doi.org/10.2307/4015
In: Journal of Animal Ecology. Blackwell Science/British Ecological Society: Oxford. ISSN 0021-8790; e-ISSN 1365-2656
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| Trefwoord |
Aythya fuligula (Linnaeus, 1758) [WoRMS]
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| Abstract |
(1) The foraging activities of wintering tufted ducks (Aythya fuligula) feeding freshwater mussels (Dreissena polymorpha) were studied in order to determine whether not prey-size selection occurred. Eight experiments with captive birds were performed calculate the profitability of the different sizes of the mussels and to ascertain preferred size classes by the ducks under controlled conditions. In two field experiments the influence of prey density and diving depth upon prey-size selection by wild investigated. (2) The experiments in captivity showed that the ducks did not prefer profitable prey, but took significantly smaller mussels. Excluding visual clues selection resulted in a further decrease of preferred mussel sizes. Being attached substrate did not affect the relative profitability of the different size classes of Selection became more obvious the more the size classes offered differed from each other. (3) The field experiments revealed that both increasing prey density and decreasing depth caused an increase in selectivity. Increasing prey density caused a transition towards preference for smaller mussels. The exact effect of decreasing depth on selectivity could not be identified, probably because the prey density used in the experiment was too low. Diving times of the ducks were strongly affected by both prey density and diving depth. (4) Three hypotheses were proposed to explain the selection of sub-optimal mussels by tufted ducks. First, the constraints of diving could change the problem of size selection, as the ducks might do better in swallowing two smaller mussels in one dive instead of one larger mussel. Second, the ducks might prefer smaller mussels to avoid the risk of taking mussels that are too large to be swallowed. Finally, as larger mussels have highly variable profitabilities, it might pay the ducks to select smaller mussels associated with less variance. The data, however, do not allow the hypotheses to be ranked according to their plausibility. |
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