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.
Life Under Water and in the Air
The pochards all dive for their food, using only their feet to move underwater (sea ducks also use their wings). These ducks are beautifully adapted for what they do, possessing compact, fusiform bodies (a plucked October bluebill reminds me of an unbaked loaf of bread), legs set well back on their torso, big feet and strong legs for propulsion, and the ability to slow their metabolic rate during dives. Most often, they dive in fairly shallow water from a foot-and-a-half to six feet deep, staying under for 10 to 20 seconds, although they can dive deeper and longer. A canvasback rooting up tubers dives straight down and comes up in the same place, while a scaup cruising through the water feasting on amphipods may surface 50 feet or more from where it dove.
To truly appreciate life as a diving duck, however, you have to watch them up close, underwater, which I've been privileged to do in experimental diving tanks. As a poor swimmer, I'm awed by how at home these birds are under the surface. Each dive begins with birds subtly but clearly depressing their body feathers. This squeezes out air, making the birds less buoyant. Next, they arch their bodies and dive with a single thrust of their powerful feet. Then, they use their "paddles" like expert oarsmen, stroking with both feet together, steering largely with their head and tail. Near the bottom, angled head-down, they use their feet to tread and maintain their position while probing the bottom with their bills, using mainly their neck muscles to move their heads from side-to-side and up-and-down. Their submerged bodies glisten with air bubbles, and when ready to surface, they simply quit paddling and bob to the surface like feathered corks.
These adaptations for diving come with a cost, however. The rearward placement of the feet, while great for diving, makes these ducks awkward on land. They are better off than grebes or loons, but much less able than, say, pintails, to walk from pond to pond with ducklings in tow. Because they have to move efficiently underwater, divers also have compact wings that lay tightly against their body. Smaller wings with less surface area means that more speed and power are needed to get airborne. So, flushing divers taxi across the water rather than jump into the air like mallards or wood ducks, and they land with a long feet-first skid. Once airborne, pochards fly with rapid wing beats. It's no accident that canvasbacks, the heaviest of the pochards, are the fastest flyers among the ducks. Think about the shape and size of the wings on a slow-moving propeller-driven airplane versus a swift, sleek jet fighter about the same size. You'll get the idea.
The Breeding Season
Frigid blue water, winter-bleached cattails, and traces of rotting ice still clinging to leeward shores—this is early spring in pothole country. The divers arrive then, soon after the first mallards and pintails. Most diver hens return already paired, but there are still flocks of drakes in urgent pursuit of the few remaining unpaired hens. The ducks' displays, chases, and courtship calls dominate the goings-on of big ponds in springtime. But in a week or two the flocked birds have paired or moved on, leaving behind the settled pairs intent on nesting.
Most canvasbacks breed in the Prairie Pothole Region, but some will nest as far north as Alaska. Redheads rely on the prairies too, but many thousands nest to the south and west in the marshes of the Great Basin. Although some lesser scaup breed through the prairies and northwestern states, the vast majority nest in the western boreal forest of Canada and Alaska, north to the tree line. Most greater scaup nest farther north than lesser scaup, mainly in northern Canada and coastal Alaska. The two species overlap broadly from about Yellowknife to Inuvik, but can't be separated reliably by airborne survey crews. Therefore, the numbers of both species are simply counted as "scaup" in aerial surveys. Ring-necked ducks have a wide breeding range across mainly forested regions of Canada, and they are the most common breeding pochard in the east.
Like dabbling ducks, scaup nest on land, usually many yards from water. Canvasbacks build large floating nests over water, weaving last year's cattail, bulrush, or marsh grasses into a platform for their eggs. Surprising to people who know them from winter waters, canvasback hens most often select tiny well-vegetated potholes for nesting, many as small as an urban yard. (These little ponds are frequently overlooked by policy makers and too easily filled in or drained by other users of the land.) Ringnecks may nest over water too, or on land close by the water's edge. Redheads are more adaptable, usually nesting over water like canvasbacks, but they'll use dry-land sites too, especially, it seems, in the Intermountain West. All pochard hens lead their ducklings to water as soon as the young are dry and may subsequently move considerable distances between ponds to find better food or avoid predators.
Changing water levels seems to be the most important factor affecting pochard reproductive success. Dry conditions mean that fewer hens attempt to nest, more eggs are eaten by predators (who find nests more easily in the narrower bands of poorly flooded cover), hens are less likely to re-nest if a first nest is lost, and any ducklings lucky enough to hatch in a dry year are less likely to survive to fly south. Because the prairies naturally alternate between drought and plenty, reproduction for most divers is also a boom-or-bust business. Canvasback nesting success has been found to vary from zero to 76 percent between years in southwestern Manitoba, one of this species' best breeding areas. For canvasbacks and redheads, nesting success and duckling survival, affected mainly by annual variation in water conditions, and year-round survival of adult females are the most important factors determining year-to-year changes in populations. For scaup and ring-necked ducks, the interplay of these factors is less well understood.
Abundance and Population Trends
Of the five species of North American pochards, only lesser scaup are truly abundant, with numbers (approximately 3 to 4 million) in the range of the more common dabbling ducks (see chart above). Greater scaup live around the northern globe but are less abundant than the smaller scaup on our continent. Scaup are common probably because they inhabit such a large breeding range, especially the vast boreal forest (more than 1.2 billion acres in Canada alone), and in the nonbreeding season they eat foods that are widely available in shallow large waters like the lower Great Lakes, Mississippi River, and the Atlantic and Gulf coasts.
The other divers have smaller breeding ranges and more selective diets and nesting habitats. While not doubting the observations of clouds of canvasbacks and redheads in days gone by, I suspect they were never as abundant as scaup or really adaptable species like mallards.
Although the numbers of canvasbacks and redheads have bounced up and down over the 50 years that the U.S. Fish and Wildlife Service and Canadian Wildlife Service have conducted breeding duck surveys (see chart above), periodically causing angst among duck managers, in fact these species' overall trend has been fairly stable. Scaup, as regular readers of Ducks Unlimited magazine know, have been declining for more than 20 years, at a rate of nearly 130,000 birds/year—and we don't know why. Ring-necked ducks, in contrast, have increased by some 250 percent, both in the traditional western survey area (see chart at left) and in the east, where surveys began in 1990.
Securing the Future
Canvasbacks and other diving ducks have suffered from the deterioration of water quality in North America. In many places of former importance to these birds (e.g., medium-size lakes in Minnesota and Wisconsin, the Illinois River, Chesapeake Bay, coastal North Carolina) their preferred submersed aquatic plants have been lost to increased turbidity (caused by soil erosion, rough fish, industrial pollution, etc.), nutrient loading, and effects of rising sea levels. In other places (e.g., San Francisco Bay, certain spots in the Great Lakes), chemical contaminants are accumulating in wintering and migrating diving ducks. On the breeding grounds, wetland drainage and filling continue to be the main threat to canvasbacks and redheads. And redheads, because so many of them are concentrated during winter in the Laguna Madre of Texas and Mexico, are particularly at risk from catastrophic shipping accidents or changes in sea level or salinity.
The story for scaup is much less certain. In the lower Great Lakes and San Francisco Bay, researchers found that scaup are accumulating levels of selenium in their tissues that would cause reproductive impairment in captive mallards, although what this means for scaup is not clear. Researchers at Louisiana State University have garnered evidence that lesser scaup on spring migration in the upper Midwest are carrying fewer nutrient reserves than bluebills did 20 years ago and, therefore, may be less well prepared for breeding. In Canada, DU scientists have demonstrated a close correspondence between the timing and places where scaup and scoters have declined in the Western Boreal Forest, suggesting that something has gone awry there, too. Before we can act with confidence to reverse the decline of scaup we need to understand better what factors have been most important in their recent downward slide.
The pochards have been important to North American wildfowling traditions for more than three centuries. The excitement they stir on cupped wings and the delights they offer when well tended and placed on the table have captured our imagination and respect.
The challenges for diving duck conservation are immense. Fortunately, doing the right things by diving ducks also means doing the right things for the health of our waters and of our grandchildren. Clean waters free of excess sediments, nutrients, and toxins mean healthy plants, clams, and ducks—and healthy people. Small wetlands secured on the prairies and functioning boreal wetlands mean a secure future for breeding divers—and everyone else dependent on those watersheds. The vision is simple; achieving it will not be. But accomplishing things truly worthwhile never is.