I was talking with some folks the other day about sifting diving duck flocks for Redheads, and the age-old problem of separating this species from Canvasback came up. It's really not that hard, and the great thing is that if you are a shape/structure birder, you can do it readily, and if not, color works too.
As to color, check the photo above. Even at this fairly great distance, Redhead heads are RED - not orangy red - but the real key is the back color. Canvasback is a very pale duck, any plumage, while Redhead is more like a scaup, with a gray back. It's also got a blue bill with a black tip. We're talking about males here, though even female Canvasbacks are paler than female Redheads.
As to structure, Canvasbacks have heads that slope. Think of a doorstop, the slanted device you stick under doors to keep them from closing. Redheads have steep foreheads and shorter bills - their heads wouldn't slide under a door.
When you're checking out Canvasbacks, or Redheads, in your field guides, check out their range maps. A number of North American birds migrate nearly as far east-west as north-south, and this pair does just that.
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