During my 3 trips to Bismarck during July, the many duck broods at Dogtown Marsh east of the capitol city received hours of my attention that provided a number of thrills, and many photos of different broods. One brood and their most distinguished female attendant stood out, as Canvasbacks tend to do, for its larger size and regal look. When I have had a chance to approach this female and her brood in my mobile blind, she doesn’t usually react much aside from always holding her head high with her sloped forehead and bill showing prominently.
After each Dogtown visit, I have shared a photograph of the hen and her brood in my Editor Afield articles (July 12th and July 19th), so I was glad to have a chance to photograph the brood again last Wednesday. The ducklings were well-feathered rather than down-covered, and more closely resembled the adult female. But wait; something didn’t look quite right. As I reviewed my photos on site through the LCD monitor screen on the back of my camera, magnifying some images to get a more detailed view, I could see that some of the ducklings suspiciously didn’t look like canvasbacks!
Indeed, the closer I looked the more likely it seemed that only 3 of the 8 ducklings were young Canvasbacks. The rest? They were most likely Redhead ducklings. What? Yep, when I returned home and took a quick look at the photos I took of the female Canvasback’s brood, it was evident that only 3 of the ducklings were probably genetically hers. The others were Redhead ducklings, which were most likely the result of one or more female Redheads sneaking onto the nest of the Canvasback during the egg-laying period to deposit Redhead eggs among the Canvasback’s own eggs.
During egg laying, ducks don’t begin incubating until they have laid all their eggs so the eggs all hatch at about the same time. The female tends to lay an egg and leave the nest until they are ready to lay again, then repeats this process until their clutch is complete, which is when they begin incubating. The periods when the hen is absent from the nest during egg laying leaves the window open for a Redhead (a species that is known to lay eggs in Canvasback nests) to lay an egg or eggs in the Canvasback nest. This activity is not widespread, but it is well-documented by waterfowl biologists. In fact, my associate Bob Stewart reported an extreme case of “parasitic” laying by Redheads, in which he found a Canvasback nest with a full clutch of 12 Canvasback eggs plus 30 Redhead eggs!
Canvasbacks and Redheads tend to utilize wetlands with similar water quality, prefer to nest among thick bullrushes above shallow water, and they are both diving ducks that feed on similar aquatic plants and invertebrates, so Redhead ducklings tend to prosper under the protection of a Canvasback hen, after imprinting on her after hatching. There certainly have been plenty of Redhead broods at Dogtown marsh this year; in fact, they may be the most common duck broods on site, with a new brood of 9 ducklings following the lead of their attentive adult Redhead last Thursday.
Well, that’s my story, and when I noticed the 2-species brood together with the adult female Canvasback, I wanted to share a documentary photo and relate some little-known information about Canvasbacks and Redheads – 2 of my favorite prairie wetlands ducks.
Article and photographs by Paul Konrad
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