Mechanics of drinking in the mallard (Anas platyrhynchos, anatidae)

Water drinking in the mallard is accomplished by a fine-tuned set of movements of upper and lower jaw and of the tongue. During immersion of the tips of the bill, the oral cavity is formed into smaller volumes containing water and into connecting tubes. Two mechanisms serve the water transport: (1) lingual and jaw movements press water from the water-containing spaces into the tubes; (2) a quantitative simulation of the shape of the oral cavity during immersion shows that the two tubes are so narrow that capillary action also contributes to water transport. Thereafter, the tips of the bill are raised until they point upward. In this "tip-up" position, water flows into the esophagus because of gravity. We conclude that, in addition to normal tip-up drinking observed in almost all Passeriformes and Galliformes, a second type of tip-up drinking may be distinguished in Anseriformes. The integration of the drinking mechanism, keeping the water inside the mouth, and the straining mechanism, expelling the water along the beak rims, is effected by specific actions of the elaborate lingual apparatus.