Summary
Red-crested Pochards (Netta rufina) have been observed feeding on plants brought by their mates to the water surface, and this behaviour has been traditionally considered as courtship feeding. In this paper I report on this behaviour and examine its behavioural context. Females fed more frequently than males on plants brought by their mates to the surface, and this behaviour always occurred among paired birds. Individuals that procured the food plants were never observed offering them to their mates, but the latter simply approached the former as they surfaced with plants. The main advantages of this feeding behaviour would be to increase intake rates, as well as to reduce the feeding costs, as no time is spent searching for food underwater. Intake rates of individuals that procured the food were negatively affected when their mates profited from such food. Probably because of this, individuals that procured the food plants surfaced immediately after the feeding interaction with smaller quantities of food than before. This may be a strategy to discourage some individuals from feeding on plants brought to the surface by their mates, because this would allow the individuals that procure the food to ingest it before others start feeding on the plants. In this light, this feeding behaviour should not be considered as courtship feeding. Depending on whether pair bonds are maintained or split before breeding, this behaviour should be considered either as food sharing or tolerated food theft.
Zusammenfassung
Bei Kolbenenten (Netta rufina) kann man beobachten, dass sie Pflanzen fressen, die von ihrem Partner an die Wasseroberfläche gebracht worden sind. Dieses Verhalten ist traditionellerweise als Balzfüttern bezeichnet worden. Hier werden dieses Verhalten und sein Kontext näher anlysiert. Das Phänomen trat nur unter verpaarten Vögeln auf. Die Weibchen nahmen den Männchen häufiger Nahrung weg als umgekehrt. Individuen, die die Nahrung beschafften, boten sie nie direkt ihren Partnern an, sondern die Partner näherten sich einfach den auftauchenden Vögeln. Der Hauptvorteil für die parasitierenden Vögel besteht wohl darin, dass sie ihre Nahrungsaufnahmerate vergrößern, aber dabei keine erhöhten Kosten haben, da sie für das Nahrungstauchen keine Zeit und Energie verbrauchen. Umgekehrt haben die tauchenden Partner einen Nachteil durch geringere Aufnahmeraten. Wahrscheinlich erklärt sich hieraus, dass diese, unmittelbar nachdem ihnen Nahrung weggenommen worden war, mit geringerem Nahrungsvorral auftauchten als vorher. Dies könnte man als Strategie auffassen, andere Individuen davon abzuhalten, Nahrung zu stehlen. Sie wären nämlich mit dem Fressen so schnell fertig, dass ein anderes Individuum keine Zeit zum Stehlen findet.
Jedenfalls sollte diese Form des Nahrungserwerbs nicht als Balzfüttern bezeichnet werden. Je nach der Art der Paarbindung sollte man eher von Nahrungsteilen oder toleriertem Diebstahl sprechen.
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Amat, J.A. Courtship feeding, food sharing, or tolerated food theft among paired Red-crested Pochards (Netta rufina)?. J Ornithol 141, 327–334 (2000). https://doi.org/10.1007/BF02462242
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DOI: https://doi.org/10.1007/BF02462242