This silver teal Spatula versicolor with its bill open shows a row of thin tooth-like structures. These are the lamellae, structures typical of the sieving bill of filter feeders. In the upper mandible there is another row of lamellae which is barely seen. Ducks (Family Anatidae) are among the filter feeders. All the duck species have lamellae to an extent, though not all the lamellae are the same. In fish eaters (none in the reserve) the lamellae seem to be teeth. In geese, which may forage on land, the lamellae are less developed than in filter feeders.

When filter feeding the water or mud which has entered the bill is pushed out through the lamellae. The lamellae of both mandibles interlock acting as a colander and retaining the solid material (invertebrates, larvae, seeds, etc.). Depending on the characteristics and number of the lamellae food ítems may be as small as a diatom. The absorption and ejection of water or mud is carried out by the tongue by means of rapid movements back and forth. Besides, the tongue has hair-like structures that sweep all the material caught in the lamellae to the esophagus