DBQ answers part two

11 11 2015

And now we return to the continuing saga of dead birds. Bird B, you will recall, was little more than a skull and some other odd bone bits. Remember Bird B?

DMinsky7701-23584

Responses as to the identity of Bird B were split between common eider and some sort of goose. Indeed, this is a waterfowl type of bill, with a sloping profile and some serrations on the bill margin. The profile is quite smooth from bill to forehead, with no knob or other protrusion anywhere along the bill’s length. This is our general impression when looking at the profile of a live common eider, especially since they have those fleshy lobes that run backward up over the forehead.

Note the fleshy lobes on the eider bill, more prominent in males like this.

Note the fleshy lobes on the eider bill, more prominent in males like this.

 

If you look at the skulls of eiders, which you can do at Wouter’s skull site here, you can see the bone structure that underlies those lobes in the rearward projections over the forehead. Our Bird Blacks these. The other respondents on this quiz listed various goose species as contenders, and to throw an additional bit of support for that into the mix, Dennis’ note when he found this bird noted that the wing bones seemed extremely large for a duck. But within the geese, which species? Responses included Canada goose, cackling goose, and barnacle goose. There is a bit of black and white feathering still adherent to the bones in Bird B, consistent with any of those three. Barnacle goose is far rarer in these parts than the other two, but not unheard of certainly. Cackling goose sounds like something unusual, until one reads a bit about it and finds out that cackling goose is the designation given to what used to be considered merely a very small race of Canada goose. Genetic analysis has determined that cackling goose is its own distinct species. Whether or not we can, from just a photo of the skull, determine if this is cackling goose or Canada goose is a dubious question indeed.

But within these geese candidates, now is the perfect time to send you over to Wouter’s Skullsite which is an absolutely marvelous resource that I know I mention often, but with good reason. If you refer to the Anatidae (ducks and geese) page of that site here, you can get a look at the comparison between barnacle goose and Canada goose. Barnacle geese in life have what we might term a “cute” face. (Cute being a highly technical term). We tend to find animal faces cute when they have outsize eyes for their faces, and if you look at the barnacle goose skull, you will see that its eye socket (or orbit) is quite large. Compare that with the size of the orbit in the Canada goose. I would argue that the overall shape of not just the orbit, but the squared off back of the skull in our Bird B as well as the length of the bill compared with the length of the skull all argue for Canada (or cackling) goose rather than barnacle goose.

Finally, we have Bird C, which presents a substantial identification challenge. Indeed, there is really not enough here to get us to species. Everyone responding figured we have a duck here, and I concur. Edward suggests there might be a tiny hint of a blue speculum, leading us perhaps to American black duck, but neither he nor I am entirely convinced of its presence. Wouter did want to venture beyond saying it’s a duck, Mark and Jim did not venture a guess (and I can’t blame them), and John Stanton took a stab in the dark and guessed Bufflehead. So how did people know this was a duck? Wouter points to the only real clue we have–the sternum.

WMumford878-14180

This affords us an opportunity to use another of my favorite sites, aves3d.org. Take a look at this image of a surf scoter sternum, rotated to reflect the same angle we have on Bird C:

Copyright Harvard Museum of Comparative Zoology and Aves3d.

Copyright Harvard Museum of Comparative Zoology and Aves3d.

There are substantial similarities here–the overall blocky shape of the sternum, the crescents cut into the rear facing edge, and the flared projections beside those cutouts. Similar enough to make a species call though? Maybe. Take a look at these comparative images of the sternae of some other ducks:
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Somewhat surprisingly, since the surf scoter seems such a close match, the black (or common) scoter is actually dissimilar to Bird C in many ways: the crescents are more pointed in the black scoter and there isn’t as much of a pinched in, hourglass shape the sternum overall. The common eider sternum beside it actually looks a bit more like Bird C, but here the lateral projections look a bit too rounded and blunted at the ends. I might actually be inclined to call this an unknown scoter. I don’t have good skeletal reference material for white-winged scoter, which would be another candidate. We don’t see evidence of a white speculum in Bird C, but these wings are extremely weathered and bleached overall, so I am not sure how much stock I really want to place in that. I think unknown scoter might be pretty good for an i.d. What say you, esteemed dead bird colleagues? As always, your thoughts or directions to additional reference material are always most welcome.

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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.





Trying to keep my cool, readers,

5 11 2015

but I just spent two hours on my DBQ answers post, then my browser crashed, and it all disappeared into a black hole, evidently. You can, I am sure, imagine my frustration. When I can regain the will to go on, I will try to recreate it all.

Sigh.





Dead Bird Quiz, late for Halloween

2 11 2015

Ghosts and goblins and zombies have nothing on actual dead things, of course, so Halloween is naturally the holiday for SEANET. Perhaps that’s why I was too busy last week to post to the blog at all. Out celebrating.

In any case, you all deserve a DBQ. Here’s a three-fer!

Bird A, found in Maine, and submitted by Barbara and Charlie Grunden:

Dorsal surface.

Dorsal surface.

bgrunden7762-23612

Ventral surface. Or, it was at one time.

Bird B, found by Dennis Minsky on Cape Cod early in October:
DMinsky7701-23584

Bird C, found by Warren Mumford, also on Cape cod:
WMumford878-14180