Dead Bird Quiz answers

1 05 2015

This quiz didn’t throw our regulars off much at all, which is no surprise since they are a crack team. I agree with all three of our respondents, who all identified this as a Thick-billed Murre (TBMU). We hardly ever get Common Murres on SEANET beaches, but we must remain alert to the possibility. And sometimes, it can be tricky to differentiate the two. The northeast SEANET Field Guide uses measurements as the decisive factor, noting that, in the Common Murre, “bill depth at gonys <1/3 culmen.” The gonys is the point on the lower bill, which is particularly conspicuous in the Thick-billed. Living up to its name, the TBMU has a greater depth at this point. Overall, the bill looks different as well, having a much straighter appearance in the Common Murre. The feature I find particularly useful is the presence or absence of a light gape line running straight back from the corner of the mouth in TBMU. It is not present at all times or all ages, so its absence is not decisive, but its presence definitely indicates TBMU.

Common Murre

Common Murre

Thick-billed Murre

Thick-billed Murre

From these images, it appears that the bill on a TBMU is considerably shorter than that of a COMU. In fact, this can indeed be a useful factor when available. COMU culmen is reported in the range of 39-46 mm, while TBMU range from 30-38 mm.

For Bird B, where we have another beak in closeup, we have to first consider that the feathers at the base of the bill are partially missing and the remainder are matted down. This is common in birds that have been decomposing in the water, where feather and skin slip begin happening soon after death. It also makes it difficult to pick up on the feathering pattern in that area. Thus, we must go solely on the shape of the bill. The chisel-like shape, with the weight of the upper and lower bill appearing similar is reminiscent of a loon. But this appears too short, even for a Red-throated. That leaves us with the cousins of the loons, the grebes, and with something we might offer as an alternative hypothesis, an American Coot.

For prospects among the grebes, we have the Pied-billed, Horned, and Red-necked. When looking at our Bird B, we have both the color and the shape of the bill to go on. However, in dead birds, we must always remember that color can fade and shift with time, so if color and shape seem not to agree, best to defer to shape. And in this case, we have a very pale bill, but that may not be a true finding. As for shape, our Bird’s bill doesn’t look as stubby as a Pied-billed, nor as loon-like and spear-looking as a Red-necked. So, how about the mid-range option in grebes, the Horned?

Pied-billed Grebe. Don't rule it out; the black band is absent in non-breeding adults. (Photo: Factumquintus via wikimedia commons)

Pied-billed Grebe. Don’t rule it out; the black band is absent in non-breeding adults. (Photo: Factumquintus via wikimedia commons)

Red-necked Grebe. (Photo: USFWS)

Red-necked Grebe. (Photo: USFWS)

Horned Grebes have a dark bill when in breeding plumage, but a lighter gray one in the non-breeding season, as you see in the bird here. In that excellent photo, you can make out the whitish tip to the bill. I can’t claim to see that in our Bird, but, then again, all the color appears fairly well washed out of our bird’s bill.

Finally, just because it had occurred to me as the “out of left field option,” why is this bird not a coot? Laying aside the existential aspects of that question, the color of the bill in Bird B actually matches coot somewhat better than grebe, but our Bird B shows a clear flex point where the upper bill meets the head. In a coot, this would be a continuous slope, like such:

American Coot (Photo: Trisha Shears via wikimedia commons)

American Coot (Photo: Trisha Shears via wikimedia commons)

Additionally, a coot or moorhen has more of a droop to the bill tip, unlike our Bird B, which has a quite straight and self-respecting outlook on things.

So, we’ve got a TBMU and a HOGR. That still leaves the severed leg, but this post is overlong already and I have not yet had my supper. Next time, the i.d. revealed, and an anatomy lesson on wing versus leg propelled divers. Until next time, Seanetters.



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