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Karin Gottlander, Parental Feeding Behaviour and Sibling Competition in the Pied Flycatcher Ficedula hypoleuca, Ornis Scandinavica (Scandinavian Journal of Ornithology), Vol. 18, No. 4 (Nov., 1987), pp. 269-276
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Karin Gottlander (1987) studied this question.
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