DBQ, part deux

17 03 2015

I have feeling so very remiss about SEANET lately, not least because I cannot blog as frequently as I might like during the high teaching season. To partly make up for this, in this second installment of the most recent DBQ, I have labeled photos with orange arrows. This way, it will appear that I have been doing something more substantial than my usual.

The features I elected to label with orange arrows are not entirely arbitrary. When I looked at Bird B’s photos, my instant thought was “This is a loon.” Of course, that kind of bolt from the blue is insufficient to a DBQ answer, so I then took my usual next step, which is to ponder what it is about the overall Gestalt of this carcass that brought the word loon instantly to my lips. First, the sternum shaped (not labeled with an arrow.) It’s elongate, which, as Edward also pointed out, makes this not a grebe, which is the other pointy-beaked, white-under-winged group of birds one might consider for this i.d. Second, the small bit of patterning visible on the back feathers (shown with orange arrow).

Can you make out the faint, light colored chevrons tipping the otherwise dark feathers? That’s a loon thing. What kind of loon though? We have at least some of the head to work from, though the mandibles have parted ways from the upper beak, complicating matters. Still, take a look at this helpfully labeled photo:

Here, we can see a v-shaped white patch at the base of the upper bill. This is quite suggestive to me of a Red-throated Loon, as no other loon has such extensive white on the face, especially in the region extending up the forehead from the bill base. Without the usual hallmark of the RTLO though–the jaunty and somewhat smugly upturned look to the bill–it’s not a slam dunk i.d. As Edward pointed out, the upturned appearance of the bill of RTLO is largely due to the shape of the mandible, the upper bill being actually quite straight, as in this specimen. Alarmingly though, Edward suggested Bird B might be NOT a RTLO, but an Arctic Loon! We have never, in the history of SEANET, gotten one of those. Given this dearth, I am tempted to heed that old vet school warning about jumping to rare diagnoses: “When you hear hoofbeats, think horses, not zebras.” But then I am whipsawed by indecision when I consider all my rotations in zoos, and the memorable day I got to blow dart a zebra with its vaccinations. And then, coming out of my reverie, I remember about identifying Bird B again.

I perused the internet for some nice photos to share with you, and I found one by someone else in the world who likes to photograph rotten old carcasses! Here is a mostly skeletal Arctic Loon (known in other parts of the world as a “Black-throated Diver”:


Photo by Miika Silfverberg via wikimedia commons

You may note that this species has what looks almost like a droopy, downturned bill: just the opposite of what we see in a RTLO. And here is a cartoon version of the birds by L. Shyamal, which gets across the main aspects of their patterning:

I argue that our Bird B has more white on the face than an Arctic Loon would. Add that to the extreme rarity of that latter species in our neck of the woods, and I think I am right. But I love to argue and debate, so if anyone can convince me this is something other than RTLO, bring it on!!!




One response

18 03 2015

I’m convinced: RTLO. I had my doubts, because there is so little left and a resolution of the picture that didn’t allow a very close examination of the details such as the shape of the bill. But I agree with you on the horse-zebra thing. I was not aware of the rarity of ther Arctic Loon, so it is most likely, almost certailny a RTLO.

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