By Mike Anderson, Ph.D.
Cold wind, slate-gray sky, and angry water—most of us, if we know divers at all, know the birds on days like this. Squadrons of ‘bills boring in on the deck like WWII torpedo planes: rising, falling, dropping their landing gear, hesitating, then exploding over the decoys in every direction as they sense that something isn't quite right.
Scaup, canvasbacks, redheads and ring-necked ducks—the freshwater diving ducks, or pochards—have stirred every hunter who has known them. There's nothing subtle about a flock of divers, whether they are cans rocketing in from big water to a sheltered sago pondweed bed on a dirty, windy day; redheads streaking from freshwater ponds to beds of shoal grass in a coastal lagoon; or ringnecks pitching down to a bed of pad plants in a Florida swamp. But who are these birds, and what is Ducks Unlimited doing to help secure their future?
Meet the Pochards
The label “diver” is scientifically vague. Lots of birds dive for a living, including loons, grebes, and many seabirds. Among the ducks in North America , three distinct groups, or tribes, of species are considered “divers.” The ruddy duck represents a mostly tropical tribe known as the stifftails. The northern-dwelling sea ducks include three species each of eiders, scoters, and mergansers, as well as the long-tailed duck, harlequin duck, two species of goldeneyes, and bufflehead. Although stifftails, pochards, and sea ducks all dive for food, there are as many differences among them as similarities.
Scaup, canvasbacks, redheads, ring-necked ducks, and their cousins elsewhere around the world demonstrate their relatedness by traits other than diving. These ducks' plumages are similar—browns and grays mainly for the hens, contrasting blocks of dark and light solid colors on the males. Their wings are shades of brown and gray and may be vermiculated or include a patch of white where dabbling ducks show bright iridescent colors. Male pochards all have striking eyes (red, orange, or yellow). Like most ducks, the voices of males and females differ, and each species shows only minor variations on the common theme. The males have a unique voice box with a thin transparent “windowpane” located at the top end of the trachea. Biologists can offer a long list of such pochard traits, but the point is that these birds clearly shared a common ancestor long ago.
Similarities notwithstanding, each pochard species is distinctive according to its lifestyle. Canvasbacks are best known for their big feet, long muscular neck, wedge-shaped bill, and unique muscle arrangements that provide special strength for opening their bill after jamming it in the mud—all assets for excavating underground tubers. Canvasbacks are mainly aquatic plant eaters, concentrating on tubers or rhizomes of sago pondweed, wild celery, duck potato, and other plants (although recently many have switched to eating small clams in places like Chesapeake Bay, where their formerly important plant foods have been greatly reduced).
Redheads mainly graze on plants like musk grass or sago pondweed in the north and shoal grass in southern coastal lagoons. Like cans, they also eat tubers, rhizomes, plant stems and some invertebrates. Their bodies are similar to canvasbacks, but less specialized for digging. Ring-necked ducks eat a lot of seeds, mainly from wild rice and various pad plants, and lots of aquatic insects. The two scaup species are carnivores, eating mainly amphipods (also known as scuds, or freshwater shrimp) and small mollusks such as fingernail clams and, more recently, zebra mussels. Accordingly, scaup bills are better suited for capturing small mobile prey than for digging up tubers.