Delta Study Details Struggles of Nesting Canvasbacks

By author of The Duck Blog

Trail-camera images provide insights into predators, parasitism

Nesting canvasbacks in southwestern Manitoba face a wide array of threats, according to Delta Waterfowl research. Photo © Brian E. Kushner/Shutterstock

If you think you have it rough, try being a nesting hen canvasback in southwestern Manitoba.

Research conducted by Delta Waterfowl and reported in an article by our good friend Paul Wait, editor of Delta Waterfowl magazine, has revealed that nesting cans in that region face an array of threats to their eggs and lives. Further, biologists monitoring those ducks have captured a mind-boggling number of trail-camera images of the culprits.

For the past two summers, according to the article, University of Minnesota master’s degree candidate Michael Johnson has conducted remote-camera observations of more than 150 duck nests. He’s operated about 75 trail cameras and has collected 800,000 images. The study is part of Delta’s continuing predator-management research focused on over-water-nesting ducks, such as canvasbacks, redheads and ring-necked ducks.

“So what have all of those snapshots revealed?” Wait wrote. “That being a canvasback hen incubating a nest in southwest Manitoba is a tough task. That raccoons and mink want to devour your eggs and will kill you for them. That hawks, ravens and crows will swoop in to scramble your eggs, and your brains, too. That red foxes and coyotes will swim out to raid your nest and chomp your feathers if you linger. That coots and redheads will relentlessly harass you, and as soon as you get off of your eggs, they’ll roll them over the side to the bottom of the pond. And worse, a hen redhead will deposit her own eggs in your nest, hoping you’ll hatch her ducklings and play foster parent.”

Some of those findings were surprising, according to Dr. Frank Rohwer, president and chief scientist at Delta Waterfowl. In the article, he said biologists have speculated for decades that mink and raccoons were the main nest predators of over-water-nesting ducks. But Johnson’s research has documented a wider spectrum of dangers.

“Perhaps most surprising, (Johnson) got good evidence that red foxes and coyotes will both go into deep water for diver eggs,” Rohwer said in the story. “The prevailing dogma is that these species like to keep their feet dry. Among the other surprises, common ravens are worse predators than expected, and American coots and Canada geese were documented taking over nests and evicting diver eggs, as were muskrats.”

The article said Johnson’s trail-camera research indicated that raccoons were responsible for about 40 percent of failed nests. About 17 percent of nest failures were unknown, as no photos were captured. Displacement accounted for about 17 percent of failures, followed by avian predators, 13 percent; canids, 9 percent; and mink, 4 percent.

Johnson said in the story that raccoons were also the most persistent predators, often revisiting nests several times before all the eggs were destroyed. Mink and red-tailed hawks sometimes caught and killed hens and destroyed eggs.

The nest-parasitism images provide another fascinating glimpse into the challenges facing nesting cans. The phenomenon, in which a hen removes and/or lays eggs in the nest of another hen, is common in the study area, and redheads are the No. 1 offender. In fact, the article said that of 358 canvasback nests found, more than 75 percent contained at least one redhead egg.

Johnson’s research also revealed some positive stats, according to the story. Over-water-nesting ducks in southwestern Manitoba had about 25 percent nesting success, which is almost five times better than success experienced by grass-nesting ducks in areas of the Canadian prairie.

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