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.
The shoveler, of course, has a bill that is in a league of its own. Shovelers primarily eat aquatic invertebrates, and their extra-wide, flattened bill with well-developed lamellae helps them skim crustaceans and other invertebrates from the water’s surface.
There are distinct differences in bills between blue- and green-winged teal. During the nonbreeding period, blue-winged teal consume seeds, aquatic insects, and some vegetation, but green-winged teal primarily eat seeds, including a variety of grains. As a result, the bill of the blue-winged teal resembles a miniaturized shoveler bill, whereas the bill of the green-winged teal might be compared to the shape of a small pinky finger—the width of the bill is uniform throughout its whole length.
In contrast to mallards, two species of ducks common to bottomland hardwood forests, wood ducks and hooded mergansers, have bills that are quite specialized. The wood duck eats acorns, seeds of moist-soil plants, some vegetation, and aquatic insects. Its bill is shorter and narrower than the mallard’s because it specializes in grabbing acorns or cutting bulbs from wetland plants and swallowing them in pieces. Because the hooded merganser primarily eats small fish and aquatic invertebrates, its bill is long and narrow, resembling a pair of needle-nose pliers capable of demobilizing its prey.
The bills of diving ducks are also interesting. For example, canvasbacks use their stout, wedge-shaped bill to grub or rip tubers and roots of aquatic plants, whereas redheads are more like aquatic browsers and eat stems and leaves of submersed plants. As you might expect, the canvasback has a longer and heavier bill and a thicker, more muscular neck than the redhead.
We often see several species of geese in the same open green fields, but they are not necessarily eating the same foods. Snow geese uproot grasses and sedges to eat roots, rhizomes, and bulbs, while Canada geese shear off short grasses above ground. The bill of the snow goose is much higher than it is broad at the base, which gives the impression that the bird is smiling. The bill of a large Canada goose is stout but appears straight rather than curved like the bill of the snow goose. Although both geese eat waste grain, their bill adaptations evolved long before the advent of agriculture. Snow geese historically wintered along southern coastal wetlands and ate tubers and roots of marsh grasses and sedges. Long ago, Canada geese adapted to forage on seeds and herbaceous plants in river bottoms and probably in upland fields that contained short, new growth of green grasses. Today, agricultural fields are smorgasbords for these geese. Both species eat a variety of grain at specific times and places. However, Canadas still savor the stems of short green shoots, like wheat or barley, while snow geese grub the roots of these and other plants.
Nature has modified characteristics of waterfowl species so that they can exploit different types of foods. This allows them to coexist in the same habitats without much competition for food. Next time you are waterfowl hunting or just watching ducks and geese, study their modes of feeding and think about how they have developed great tools for accessing their favorite foods.
Dr. Brian Davis is a DU regional biologist based in Little Rock, Arkansas.