If you look at the bills of some duck species, you may see it lined with fine comb-like structures. These little projections are called lamellae and are made of keratin. These slightly flexible structures are used to filter and strain food from mud or water. These structures will be seen mostly in dabbling ducks along with geese, swans, flamingos and other waterfowl.
As the duck sifts through mud and vegetation, these lamellae help trap seeds, bugs or other possible foods while being able to expel the mud and water through this built-in filter.
The length, spacing and number of lamellae will vary between species. Most dabbling duck species have about 50 to 70 lamellae. Both the blue-wing and green-wing teal have about 120, shovelers can have about 110.