The Can

There are something like 16 species in the subfamily Anatinae that show up regularly in the waterfowler's bag, but face it, when somebody says "duck," we think "mallard." This isn't to say that hunters aren't pleased to welcome a flock of teal or wigeon or an occasional black duck into the decoys, but the morning that ends with a limit of greenheads is just a bit brighter.

It wasn't always so. Back when the waterfowl market was still legal, the going rate for ducks reflected a different hierarchy. The menu at Baltimore's Rennert Hotel was typical--the going rate for a mallard was $1.50; the price for a canvasback was $3. J.C. Jackson, a Baltimore wholesaler who specialized in poultry and waterfowl, paid up to $7 for a brace of cans fattened on wild celery in Chesapeake Bay.

Sportsmen of the era held the can in the highest regard. On a January hunt in 1900, outdoorsman and naturalist George Bird Grinnell visited Currituck Sound for a few days of shooting. A few weeks later, he wrote: "I have recently had the opportunity of being brought into what I may call close association with the greatest of all the wildfowl, the superb canvas-back duck."

The change in loyalties between Grinnell's time and ours was probably a simple matter of numbers. Most North American ducks suffered major declines in the late nineteenth and early 20th centuries as marshes were filled, drained, and polluted, but the canvasback seemed to have been particularly vulnerable. In the late 1930s, when most ducks rebounded, thanks to restrictive hunting regulations and the first efforts to set aside habitat, the canvasback failed to respond.

The old timers in the Atlantic and Mississippi flyways knew that cans doted on wild celery during the fall and winter; in fact, when the ornithologist Alexander Wilson proposed the first scientific name for the species in 1814, he dubbed it "Anas valisneria," Latin for "wild celery duck." At the turn of the last century, wild celery or eelgrass was a canvasback staple across the eastern third of the continent. Sadly, the great beds of wild celery didn't thrive in the conditions that came with the 20th century.

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Some observers were convinced that a disease attacked the plants; others thought that incursions of salt water from canals caused the decline. Silt from widespread sheet erosion may have changed the bottoms of many marshes, discouraging the celery. Exotic plants like Eurasian milfoil and Hydrilla may have out-competed the native plant in some situations, and burgeoning schools of carp may have rooted out many stands.

Whatever the causes of the decline in wild celery, the result was the same. In 1947, a duck hunter on the Eastern Shore of Virginia wrote that local creeks once "fairly swarmed with canvasback, redhead, scaup, blackduck, Canada geese, brant, and swan.

But with the eelgrass went the ducks." Two years later, a Minnesota hunter wrote with nostalgia that "the celery brought the canvasback. Heron Lake was one of the greatest canvasback concentration points in the country. . . . By 1922, the celery vanished. The Canvasback have never returned in numbers."

Seventy-five years later, the canvasback has still not returned "in numbers." Since the continental surveys of waterfowl began in 1955, the populations of breeding canvasbacks has fluctuated around 600,000 birds while the mallard population has been running around 8 million. Little wonder that recent generations of waterfowlers have transferred their allegiance to the mallard, a more adaptable bird that has found a way to prosper on landscapes the can has not been able to exploit.

The case of the canvasback is intriguing. Cans haven't shown the steady downward trend that has so worried aficionados of the pintail and lesser scaup, nor have can numbers followed the steady climb of gadwall or green-winged teal. The graph of canvasback populations through the years seems to show two phases--a 30-year span where the average breeding population was about 560,000 and the following 23 years when numbers averaged about 590,000. If there was a pivot point, it was 1985.

Ask any statistician to look at this graph, and he'd tell you that there is no significant difference between the two eras, that the most important characteristic of the data is wild fluctuation. Cans hit rock bottom in 1962 at 360,000 birds; two years later, the population had almost doubled to 644,000. In 1978, the population dropped to 373,000; two years later, it had rebounded to 735,000. In 2007, the population peaked at 865,000; last summer, it dropped to 489,000.

More than most ducks, the canvasback's fortunes on the breeding grounds are tied to water. Cans typically nest over two or three feet of water, building their nests in stands of cattails or bulrush. It's a good anti-predator strategy--as long as the moat remains. In a dry summer, many nests that were built 50 feet from shore in April end up with dry land under them before the clutch hatches. A patrolling raccoon or mink can hardly miss them. If the hen manages to hatch her brood, she generally leads them to bigger water.

Canvasback hens are known for their wandering ways-- they may move their broods from one marsh to another three or four times before the ducklings are old enough to fly. These overland trips are fraught with danger for the youngsters and account for a large portion of the summer's losses.

Then there is the redhead problem. Redheads have a habit of laying their eggs in nests that aren't their own. The biologists call this nest parasitism, and it's a special problem for canvasbacks. Since the two species use many of the same places during the summer, redheads lay an unusually large number of eggs in canvasback nests, and there is some reason to believe that canvasback hens don't lay as many of their own eggs when they see a few redhead eggs in the clutch. Fewer canvasback eggs lead to fewer canvasback ducklings and, eventually, fewer breeding hens.

For years, I dismissed this phenomenon as one of those facts of nature the can has always faced--since there have always been redheads looking for a free ride, it was hard to use them as a partial explanation for the canvasback's recent troubles. But the mechanism may be more complex than it first appears.

Given a choice, cans prefer to nest on relatively small potholes while redhead hens gravitate toward much larger marshes. On the pristine prairie, this difference may have kept most canvasbacks clear of freeloading redheads, especially in wet years when the whole landscape was wet.

Unfortunately, the small potholes are the first to disappear during a drought and the first to be drained by farmers looking for more acres. Is it possible that we've spent the last century eliminating the canvasback's preferred nurseries while we've gone out of our way to preserve more permanent marshes that suit redheads? Have we forced the can to cohabit with a parasite?

Whatever the forces at work, there's lit

tle doubt that the can has done little more than hold its own over the last 60 years. If water conditions in the northern prairies and parklands are the key to canvasback production, the future looks grim. Climate experts expect that these areas will tend to get drier as average temperature rises over the next century. At the same time, rising sea level will bring more salt water into the bays and estuaries that produce the forage canvasbacks prefer during the winter. This invasion of salt will be good news for the redhead, bad news for the can.

We could help them more if we understood them better. Researchers still face challenging questions about canvasback biology and management. I hope we will answer them. The can will never be the staple it once was for waterfowlers, but while the flocks of mallards blur through course of the season, that one drake canvasback ripping by on a north wind will always be the event of the year. "The king of our ducks," George Bird Grinnell called him. Long may he reign.