Parental Feeding Behaviour and Sibling Competition in the Pied Flycatcher Ficedula hypoleuca

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Abstract
The begging behaviour of nestlings and feeding response of parents were studied in six Pied Flycatcher broods in an unmanipulated sequence followed by an experiment where nestlings closest to them, but also begging intensity influenced a nestling''s probability of receiving food. Probably because of the relatively slight weight spread among the nestlings, no difference in begging behaviour according to weight could be detected. In the experiment, heavier nestlings were, on average, significantly closer to the optimal position than in the natural situation. The nestlings tried to remain in the optimal position and had better chances to obtain two feeds in sequence during the experimental than during the unmanipulated period. Females tended to distribute food less evenly than males and to favour light nestlings; hence there may be a potential for parents to counteract sibling competition leading to an asymmetry of food allocation. However, this tendency was not observed during the experiment. A trade-off may therefore exist between the amount of time that can be spent identifying particular nestlings to feed and other activities.