by Michael G. Anderson, Ph.D.
It was a tiny pothole, with a patch of cattails in the middle no bigger than a suburban living room, yet I knew she was there, sitting on a floating platform of broken cattails and new green shoots. We couldn't see her as we glassed the pond from the knoll to the northeast, so we moved quietly to the edge of the water. Finding just the right angle to peer into the cattails I spotted the hen—head down, neck outstretched, relying on stillness and her mottled feathers to hide her on the nest. We took a cautious step into the water but my companion caught his boot and splashed just a bit. Silently L-3, a four-year-old canvasback hen known by her green and white plastic bill marker, slid into the water, swam to a small opening in the cattails, and launched away into the wind with the patter of feet and an alarmed grrrack, grrrack, grrrack, grrrack!
I turned to my open-mouthed companion, a visitor from the Eastern Shore of Maryland, who was sputtering something about "Really? A pond this small? Why in the world? What is she doing here? I never would have believed..."
It was a familiar reaction of people who know canvasbacks largely from their big-water wintering grounds. In places like Chesapeake Bay, where "cans" are the stuff of legends, the birds congregate in big rafts on rolling waters like you see in a Ron Van Gilder painting, where getting close to the birds means lying low in big waves or patiently waiting in a wind-swept hide anchored near a shallow feeding area.
I explained that while not all canvasback hens choose ponds this small for nesting, it's not unusual. The late Jerry Stoudt of the U.S. Fish and Wildlife Service (USFWS) found 2,511 canvasback nests during 12 field seasons while wading around a southwestern Manitoba study area, mostly with his old Lab, Lisa Jane (who, like her master, harbored a serious hatred for raccoons). Stoudt, who logged more miles in hip boots than most of us rack up on Michelins, found that 65 percent of hen canvasbacks in his study area nested in ponds less than one acre in size despite having a wide array of wetlands from which to choose, and a remarkable 41 percent of canvasback nests were built in ponds less than a half-acre in size.
I studied canvasbacks for a while, too, in the same pothole country just south of Minnedosa (from 1975-1990) before I moved from Delta Waterfowl to Ducks Unlimited. In this area, breeding canvasbacks are as abundant as anywhere else in the world. In fact more than 10 percent of the world's population of these prized but uncommon ducks nest in the 10,000 square miles of knob-and-kettle terrain in southwestern Manitoba. If you drive by Minnedosa some day, look for the statue of the flying canvasback at the rest area at the junction of PTH 10 and HWY 16, erected by the town in recognition of the unique connection between this duck, waterfowl researchers, and this agricultural community.
The Perfect Combination
Canvasback hens prefer to nest on heavily vegetated ponds with deep enough water to provide some protection from land-based carnivores like skunks and foxes. They also prefer to dine on the tubers of sago pondweed, a plant that requires permanent water to thrive. In this corner of Manitoba and parts of neighboring southeastern Saskatchewan there seems to be a magic combination of the right basin shape and depth, the right mix of permanent and more seasonal ponds, and the right water and soil chemistry to produce the nesting cover and foods the birds favor (sago and abundant aquatic insect larvae), and voilà—canvasbacks in good numbers.
Consistent with this reliance on dependable food and nesting conditions, in this region canvasback hens show extreme loyalty to previous breeding areas. The vast majority of canvasback hens return to the same home range they occupied in previous seasons. We know this from marking lots of birds with individually identifiable nasal "saddles," which allowed me to monitor the locations and behavior of one hen for as long as 12 years. That case was exceptional, but many hens having reached adulthood returned to the same breeding areas for several consecutive years. About 25 percent of marked female ducklings came back too, a proportion only slightly smaller than the number that we had estimated would survive their first year on the wing.
"One thing that remains constant between the wintering grounds and breeding grounds," I told my visitor, "is that canvasbacks rely on wetlands."
Photo: U.S. Fish and Wildlife Service
Unlike dabbling ducks that nest and sometimes feed in uplands (mallards, pintails, American wigeon, and other species at certain times and places), canvasbacks do everything on or under the water. Canvasbacks leave the water only to preen and oil their feathers, have a snooze, or maybe conserve body heat. And brood hens sometimes waddle as quickly as possible between potholes with a brood in tow. But canvasbacks and other diving ducks, with their feet placed well back on their bodies in order to paddle efficiently underwater, win no races on dry ground.
So put simply, conserving canvasbacks is all about conserving wetlands. "That may sound straightforward enough, but it's challenging," I said as my companion snapped yet another photo of the tiny nesting pond, an image that surely would be trotted out for display to unbelieving colleagues back home. The nest bowl held seven olive-buff canvasback eggs and a single parasitically laid cream-colored redhead egg, a common clutch for early incubation.
I explained that canvasback pairs occupy large and broadly overlapping home ranges—about one to 1.5 square miles here—and within that range use a dozen or more wetlands during the breeding season. Bigger ponds with good carbohydrate food supplies (especially sago tubers) are preferred by the birds when they arrive in spring, and the birds initially spend most of their time feeding, recovering from their long journey, and making ready to nest. As females begin to develop eggs they often seek out smaller seasonally flooded wetlands with abundant high-protein, calcium-rich invertebrates to nourish egg formation. They also begin to travel more widely, obviously exploring potential nesting ponds. "Many of these," I reminded him, "are smaller well-vegetated ponds like this."
If hens are lucky enough to hatch a clutch they lead their self-feeding ducklings to ponds with appropriate food for their developmental stage. Typically broods move to successively larger and more permanent ponds over the nine weeks or so that hens look after their ducklings. Such moves occur as the ducklings' high-protein diet begins to include some plant matter and smaller wetlands recede as summer wears on.
This pattern of movement means that canvasbacks use a wide array of wetlands between their spring arrival and autumn departure. Just conserving the big ones (where many of us tend to see ducks when we are afield in the fall) won't cut it. Nor will "consolidating" small ponds into larger ones as the agricultural industry would like to do. And protecting them all is difficult because the smaller ones in particular are a nuisance to grain farmers, who have to operate around them with bigger agricultural implements than their grandfathers ever imagined. Some combination of incentives and regulations will likely be necessary to ensure canvasbacks have the wetland habitat required to sustain their current numbers.
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