H. Albert Hochbaum, who studied under Aldo Leopold, in his book The Canvasback on a Prairie Marsh described a flock of ducks “Swinging now high, now low they course the ice field for many minutes until finally, breasting the wind that carried them north, they alight with a swish in a dark pool at the edge of the ice. They rest nervously, heads up and alert, white-backed forms rocking in the water like chunks of ice. The “Cans” are back!
The scene at Goose Pond on March 14th reminded us of the above passage where there was about one-quarter acre of open water. It was a treat to see a small flock of 15 cans circle and land. March 14th was a wintery day, 340 tundra swans and 220 greater white-fronted geese were hunkered down trying to conserve energy while 96 canvasbacks were swimming in the open water. Luckily for the waterfowl, the pond was completely open three days later. With a top-end speed of 70 mph, canvasbacks are North America's fastest duck and also the largest duck.
Canvasback numbers stayed fairly consistent for the next week and ranged from 80 to 100. On some days, cans were near the road and provided birders and wildlife photographers with good viewing opportunities. It was unusual not to see any redheads on the pond. The males of these diving ducks with red heads can be distinguished apart by the canvasback’s white body and sloping forehead compared to the redhead’s gray body and head similar to other ducks.
Novice bird watchers could easily observe that the sex ratio was heavily skewed to males and that the cans were establishing pair bonds on migration. Predation on females during the nesting season helps contribute to the imbalanced sex ratio.
In the mid 1950s, the canvasback population numbered around 600,000. In the 1980’s and early 90’s, there were some years when cans numbered around 400,000 and the canvasback season was closed. Loss of breeding and wintering habitat and lead poisoning due to ingestion of spent shot while feeding lead to the low numbers. When lead shot was replaced with steel and water returned to the prairie pothole region of the Dakotas and Canada their numbers increased. In the past few years their population has been around 750,000 individuals and there is a hunting season with a two bird daily limit. The place to see tens of thousands of canvasbacks in fall is the Mississippi River in late October and early November.
Canvasbacks migrating through Wisconsin are probably from wintering grounds in the mid-Atlantic and the Lower Mississippi Valley. Historically, the Chesapeake Bay wintered the majority of canvasbacks, but with the recent loss of submerged aquatic vegetation in the bay, their range has shifted south towards the Lower Mississippi Valley. Brackish estuarine bays and marshes with abundant submerged aquatic vegetation and invertebrates are ideal wintering habitat for canvasbacks. At Goose Pond the canvasbacks, redheads and tundra swans feed on the arrowheads (duck potato) tubers. Often the cans and redheads feed close to the swan hoping they can snatch a tuber or two from the swans.
Someone asked us recently if canvasbacks nest in Wisconsin. In the first breeding bird atlas from 1995 -2000 there was a possible breeding record of canvasbacks from Rush Lake in Winnebago County. Rush Lake is Wisconsin’s premier prairie wetland. Sam Robbins wrote in Wisconsin Birdlife that canvasbacks seldom breed in Wisconsin. Robbins found records of canvasbacks nesting in six counties from 1892 to the last recorded nesting in 1976, including a 1927 record of canvasbacks nesting in Madison.
We hope you can visit Goose Pond this spring and hopefully see the “King of Ducks”.
By Mark and Sue Foote-Martin, Goose Pond Sanctuary Managers