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?

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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.

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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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9 responses

11 11 2015
Wouter van Gestel

The skull you show in this post is not an eider, it’s a female white-winged scoter. Eiders look quite different, I show several species on http://www.skullsite.com.

Wouter

18 11 2015
scourc01

Well, that is unfortunate! That material was referenced to me by someone working at a natural history museum!

18 11 2015
scourc01

Also, I definitely agree, your site is excellent, Wouter, but of course, I have to find images I can legally post in the blog itself, so I have to work within those confines. But yes, thanks for catching the erroneously posted image here.

18 11 2015
scourc01

Finally, Wouter, can you tell me whether the projections on the eider skull that support the fleshy lobes are equally prominent in both male and female Common Eiders?

4 12 2015
Wouter van Gestel

I hadn’t noticed your question earlier, so a late reply: I’m not sure whether the forehead projections in an eider differ between the sexes, I’ll check it the next time when I have a male and female skull to clean. I do know the skull shape of the common eider differs between subspecies. At my website I have European eider (Someteria mollissima mollissima and as an extra picture a Pacific Somateria m. v-nigra, which is larger with a longer bill. I also have Eastern American eider Somateria m. dresseri, which has a shorter bill, steeper forehead and larger protrusions. I’ll check with my colleague whether I can show that on the website as well, I may have to make a combined picture of both American subspecies.
By the way, if you need skull pictures you can legally use on your blog you can use those on my website. Your blog is educational and non-profit as well, therefore you can use my pics for free as long as you mention the source Skullsite.com

11 11 2015
Edward Soldaat

Yes Wouter, You are right. I just decided to post a message to find out that you are ahead of me.

18 11 2015
scourc01

oh, no wait, I linked to the wrong image! Yes, of course that is a scoter! Grrr. Let me see if I can find the eider in these files!

11 11 2015
Edward Soldaat

Concerning the duck sternum. This one looks a bit too narrow to be a scoter of any kind and it is also to much constricted in the mid section to be one. It’s overall shape look more like a dabbler if you ask me. That’s why (and because the tiny hint of blue I thought to see) I thought of a Black Duck. But one would need good reference material to be sure in this, and even then..

18 11 2015
scourc01

I think this may be good fodder for yet another post! This one focusing on sternae!

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