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The Big Four - Diving Ducks

Canvasbacks, redheads, scaup, and ring-necked ducks are North America 's most numerous and beloved divers 
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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.

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