No more shirking or dodging; I must at last face those wings known as Bird B. To jog your memories, here’s what we’re working with:
Dennis, who found the wing, wondered if this might not be something other than a standard issue species. Everyone who has looked at the wing (and ventured to reply) concurred that this is a loon of some kind. The clean white underwing by itself could indicate a few different species groups, including shearwaters and grebes. But looking at the upper wing, we see buff colored chevrons at the terminal ends of the secondary coverts. The wing chord looks to be around 28cm. These features together tell us this is a loon, and a pretty small one (common loons have a wing chord in the 33-40cm range). Red-throated loon is the default i.d. for a small loon on the east coast, but it’s not the only possibility. Dennis granted that it could certainly be a RTLO, but thought something just seemed a bit off about in terms of its overall coloration and the nature of those pale chevrons. Since Dennis has seen many, many a dead bird, I think it worth a look when he notes something atypical about a carcass. Dennis thought perhaps Pacific loon should be on our consideration list. If we consider Pacific, we should also consider Arctic since the two are almost always uttered in the same breath and can be difficult to distinguish themselves. Both Arctic and Pacific loons would have a wing chord in the range of Bird B’s; both average larger than RTLO, but a wing chord of 28cm would fit with any of the three species. Strangely, given what one might assume from the names, the Arctic loon would be much more of a rarity than the Pacific in these parts.
This situation calls for the use of two of my favorite resources: Peter Pyle’s identification guide, and the Slater Museum’s online wing collection. You can check out a whole suite of loon wings from various species and times of year here. Fortunately for me, they have a few Pacific loon specimens there to look over, in breeding and non-breeding coloration. As with many loons, breeding plumage includes bold, clear, pure white spots on otherwise black upper wings. Our Bird B does not have any white spots or dots at all, but that lack is typical of a bird no longer in nuptial raiment. Beyond being a non-breeding bird though, what we have here in Bird B appears to be a young bird. In the case of RTLO and Pacific loon, both have pale edges to the secondary coverts during the first year, and that first year plumage is retained into well into the first winter, so the timing is right for Bird B, which was found at the end of November. To parse out the differences between juvenile RTLO and Pacific loon wings, we can look at Peter Pyle.
Considering this, I am of the opinion that Bird B is decidedly chevroned and now crescented. And so, though I had fervently hoped we might have a first ever Pacific loon in our database, I fear it is not, and is, instead, our old friend the Red-throated loon. As ever though, if I am missing something critical, I know all you super-pros will write it with the correction.