By Brian Davis, Ph.D.
Part of our fascination with wetlands is that they accommodate so many kinds of birds. Quality wetlands contain submerged aquatic plants and their tubers, emergent vegetation, seeds, and aquatic invertebrates. Over millennia, waterfowl have adapted to partake of this wetland bounty.
Differences in body size and neck length allow waterfowl species to exploit these various foods to help them store nutrients for breeding or to survive winter. But just as we select the correct utensils for dining, waterfowl species have also developed different bill sizes and shapes for acquiring food.
Dabbling ducks like mallards, pintails, and gadwalls have round-tipped bills that are relatively flat, about as long as the duck’s head, and deeper than they are broad at the base. The edges of the bill are soft because waterfowl often find food by touch, feeling their food much as we sense things with the tip of our finger. Waterfowl bills have a nail at the end that is used for hooking or moving food items as we might use our fingernails to manipulate something.
Lamellae are another fascinating adaptation of the waterfowl bill. These small, comb-like structures along the inside of the bill act like sieves and look like teeth, even though ducks and geese don’t chew food. When ducks are searching for food, nonfood items such as mud and water can be expelled while seeds, bugs, or other food items are retained by the lamellae. The top part of the waterfowl bill is called the upper mandible, and the bottom part, the lower mandible. The upper mandible is affixed to the skull, but the lower mandible can move up and down. The upper and lower mandibles of most dabbling ducks have from 50 to 70 lamellae, but bluewings and greenwings may have 120 to 130 lamellae. Shovelers have about 220 lamellae on their lower mandible and 180 lamellae on their upper mandible.
Waterfowl bills are designed to allow efficient foraging. Many dabbling ducks consume a diversity of foods, but some are more specialized than others. Mallards are perhaps the most generalized foragers among North American ducks, and this is reflected in the size and shape of their bill. A mallard will eat nearly anything it can get down its throat. Mallards feed on grains, small seeds, insects, plant matter, and even crawfish, salamanders, frogs, and small fish. Because every waterfowler knows the shape and proportions of a mallard’s bill, we can use it as a basis of comparison with other ducks’ bills.
Pintails and gadwalls have similar bills that are narrower than a mallard’s because each at one time had a more limited diet. Before agricultural crops were available, pintails fed mostly on small seeds produced by moist-soil vegetation, while gadwalls mainly consumed submersed aquatic plants such as pondweeds, wigeon grass, and coontail.
Similarly, the wigeon was predominantly a grazer, and even today it frequently feeds in pastures. Its bill is stubbier and narrower than a mallard’s and therefore is better suited to shearing off the tops of green shoots. In fact, the wigeon’s bill is shaped much like the bill of a Canada goose, another grazer.