DBQ answers, saving every 30 seconds version

6 11 2015

OK, after mourning the loss of all the work of yesterday’s post, I am now ready to try and recreate it. Bird A was universally identified as a black scoter, and I’m not surprised. Given that we have both feet and wings, our odds of getting to species are fairly high. But how did everyone arrive at that conclusion? I find the feet to be the most eye-catching aspect here.

Dabbling duck foot (left) vs. diving/seaduck foot.

Dabbling duck foot (left) vs. diving/seaduck foot.

These are webbed, waterfowl type feet, but the toes are thick and fleshy, with a prominent lobe to the hind toe. These are no dabbling feet; these are the feet of a hardy, seafaring sort of duck. Within seaducks of this general size, we are looking at eider or scoter. The overall coloration of the bird is dark, so we can rule out common eider. Though males do have quite a lot of dark on them, they would also show some white, particularly on the upper surface of the wing near where the shoulder would once have been. Similarly, if this were a white-winged scoter, we would see white here too, this time in the form of the eponymous speculum. But we have a pair of wings dark throughout, and dark on both upper and lower surfaces. So we have surf scoter and black scoter remaining. In terms of the foot, if you take a look at this fantastic shot from Arkive.org, you’ll see a pretty good color match between a confirmed black scoter and our Bird A. Surf scoters, on the other hand, seem always to have some degree of reddish cast to the toes, even in the youngest birds and in females. See this charming illustration from long ago:

Surf scoters. Note even the female (left) has reddish toes.

Surf scoters. Note even the female (left) has reddish toes.

Here’s one final thing: in all our references, indeed even in the Field Guide I researched and wrote myself, one of the defining, nay, the defining characteristic that permits differentiation of a SUSC wing from a BLSC wing is the relative length of the outer two primaries. That conventional wisdom is that in BLSC, the outermost primary is shorter than its neighbors. In a SUSC, the outermost primary is equal to, or longer than its neighbor. This can be subtle, and is most helpful in a wing where the primaries have been fully extended. It’s hard to tell where the outermost primary actually ends in Bird A, even in this zoomed in image.

Closeup--is that a short primary I'm seeing there?

Closeup–is that a short primary I’m seeing there?

When we refer to a major authority on the subject, Carney’s guide to waterfowl based on wing plumage, we see an artist’s rendition that looks much clearer, not surprisingly, than field conditions often are.

Reference: http://digitalmedia.fws.gov/cdm/ref/collection/document/id/1407

Reference: http://digitalmedia.fws.gov/cdm/ref/collection/document/id/1407

It may be the power of suggestion, but the more I look at Bird A’s wing, the more convinced I am that I am seeing a skinny little outermost primary overlain on a broader, longer, next-door-neighbor primary. So, I find myself on board the Black Scoter train with all of you.

Now, on to Birds B and C, but at the moment, I am out of time, and if I break this into a two part cliff hanger, I will have something to write about next week. I’ve been at this blogging game a while now, folks, and I’ve learnt a few tricks. See you next time for the further installment of DBQ answers.

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