Dead Bird Quiz answers…if I had some

28 07 2015

This latest quiz was a challenge, not least for me. Mary Wright wrote in about Bird A (just a sternum actually) saying that she has no idea, and I felt the same. I admit, as a seabird oriented sort of person, I am blindered to the other orders of birds, and there is no reason this has to be a seabird, just because it was found on a beach. I have tried to keep my mind open in terms of identifying this sternum, but it may still not be open enough. Luckily, we live in an era of complex algorithms where computers can do many sorts of work, including identification of images. Unluckily, I operate in a less technical world where I like to utilize the “shot in the dark, based loosely on gut feelings,” technique of identification. Understanding this, let us begin.

Bird A: Found in North Carolina.

Bird A: Found in North Carolina.

It’s a bit diffcult to gauge the size of this sternum, given its angle, and it is both foreshortened and enlarged by the camera. These distortions are a complication. I don’t really want to venture any guesses as to size, so I am doing what I can with shape. The first thing that jumped into my mind was a pouch bill like a pelican, perhaps. What bothered me about this is that pouch bills very often have a furcula (or wishbone) that is fused to the forward point of the keel. Where the fingers are gripping the tip of the keel, there appears to be nothing attached, nor a broken end of any sort. This does argue against pelican and friends. There are also those projections curving off the lateral surfaces of the sternum. Those are odd, and not something in keeping with any of the standard issue seabird keels I look at all the time. There is a keel, but it tapers off about mid sternum, so that the back end of the sternum is pretty flat with no central ridge. This caught my eye as well, since most birds we deal in have a continuous ridge all or most of the way to the back end of the sternum.

Given all this, I decided to pull up one of the coolest resources I know of when it comes to identifying bird bones. Aves3d.org allows you to view and manipulate 3D images of various skeletal elements of many, many bird species. These specimens are not just from North American birds either; you can rotate the sternum of an emu through 360 degrees if you so choose. And I do. In the case of our mystery sternum, Aves 3D allows us to look up various sternae, and then rotate them into a similar position as we see in our photo from Bird A. Check out this image of a White Pelican’s sternum, which I rotated into such a position:

White Pelican sternum. Photo copyright Yale Peabody Museum and Aves 3D

White Pelican sternum. Photo copyright Yale Peabody Museum and Aves 3D

Where this sternum is consistent with Bird A is in that tapering of the keel to a flat surface a little more than half-way down the sternum’s length. Compare that with a sternum that is much more typical of other orders of flighted birds:

Sternum of a Scaled Pigeon. Photo copyright Harvard Museum of Comparative Zoology and Aves 3D.

Sternum of a Scaled Pigeon. Photo copyright Harvard Museum of Comparative Zoology and Aves 3D.

In this pigeon, the keel is much more prominent, which is typical of birds that use fast, flapping flight. The keel is very large in order to provide attachment for the robust pectoral muscles. The keel, then, is very much unlike Bird A’s. But this pigeon does show the lateral projections of Bird A, and I have struggled to find many other birds that possess such a feature.

As I browsed through Aves3D, selecting birds fairly well at random, I came across this Black Stork.

Black stork sternum. Photo copyright Harvard Museum of Comparative Zoology and Aves 3D.

Black stork sternum. Photo copyright Harvard Museum of Comparative Zoology and Aves 3D.

I include this one mainly for the rounded silhouette of the back end of the sternum, which is very like our Bird A. Bird A lacks those longer, rearward pointing projections, but Bird A’s sternum looks rather weathered, and those long bits are often the first to snap off, so we should entertain the idea that we are missing some bits.

In the end, I remain puzzled. It’s summertime, so response rates to the DBQs are in their usual summer slump. I may recycle this one at a later date, or, I may just watch many, many more hours of my life get swallowed up by playing with images on Aves 3D. If you decide to do the same, be aware that I had to update my Java, and also change some weird security certificate on my computer in order to be able to view the images. Hopefully, you will have a smoother ride.

Tomorrow, I will post the answers for Bird B. I know, you can’t bear the suspense! But you must. Because I have to take my kid to summer theater camp. The glamour!

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6 responses

28 07 2015
Edward

My idea is that this sternum belonged to a common loon. The aspect is a bit strange because of the angle in which it is photographed. Here a pic that I stole from the internet.

28 07 2015
scourc01

Loon is on the list, and is actually what the finder thought it was. If we assume the distortion is totally blocking the rib attachments, then I’m with you. I think I will use the original photo as the poster child for why pics should be taken head on!

28 07 2015
scourc01

I can’t actually make the rib attachments disappear at any angle on the loon, but I agree, it’s a close match in other respects, and is the most likely candidate. I just held out hope for the emu. Or dodo.

28 07 2015
Edward

I’ve been fiddling with the sternum of a common loon from my collection. I attach a pic taken at the same angle. Not ther Yellow-billd Loon in the back ground. 🙂

31 07 2015
Emily

You all are fantastic, thank you! Plus, I love a little personal vindication of my limited bird bone ID skills… 😉
I know just who to contact next time I am offered an awkwardly-positioned image of a bird sternum!

18 08 2015
scourc01

Satisfying, isn’t it?

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