Not only did I get FOUR responses on this latest quiz, but all four respondents were in full agreement and concord on what these specimens were. This might well be a first. While I love a good debate, I also love feeling like our database identifications are being backed up in quadruplicate. John, Wouter, James, and Edward all submitted Common Tern, Common Loon (Edward using the European name that I adore, “Great Northern Diver”), and Sooty Tern (juvenile) for our candidates. I am not always strongest on tern i.d. in particular, so I was especially happy to see my suspicion that Bird A was a COTE fledgling had been backed up by very smart and experienced people. That still does not, however, discharge my responsibility to explain how we reached these i.d.’s. Let us begin with Bird A.
It’s a tern, certainly, and so we need to note the features that can help us differentiate terns. We’ll leave aside measurements for now, though size is a big factor in making the i.d., and look at appearance.
This bird has a pale, orangish bill with a darker tip, a dark cap, pinkish legs, and a scalloped pattern over the mantle with a darker black bar running over the mid wing. The tail is moderately forked, I would say, with a thin black line running along the outside edge of the outermost tail feathers. That scalloping on the back suggests that this bird is a youngster, hatched this summer. The possibilities that came to my mind given at least some of those features were Common Tern (COTE) and Least Tern (LETE) juveniles. Young birds can be particularly tricky as they acquire adult characteristics gradually. A feature like the depth of the tail fork, for instance, that would be of considerable use in an adult, can be difficult to judge in juveniles. We can presume, at least, that the depth of the tail fork in our Bird A has not achieved its ultimate, adult appearance.
The presence of the dark lines running along the outside of the tail, however, is useful. This feature is present in adult COTE, but not in LETE. The leg color can also be useful. While adult COTE have either black or reddish legs (depending on season), very young birds have pale orange or pinkish legs. LETE, on the other hand, have more yellowish legs when very young. COTE fledglings also have a more complete black cap than LETE of similar age, which I can persuade myself is the case for Bird A. Finally, when we add in the measurements, this bird is a good deal larger than a LETE would be. Putting all this together, my vote was for COTE, and it seems you folks agree. Any other characteristics you found useful in making this call, dear readers?
For Bird B, despite the degraded state of this carcass, it was clear to our respondents that this was a Common Loon. This specimen drives home the point that in many cases, an i.d. can be made based on the feet alone. Loon legs are distinctive in their side-to-side flatness, and adding in the tarsus length, we know this is a large loon, telling us we have a Common, rather than a Red-throated Loon here. A nice simple one.
Bird C was also fairly simple–this is a juvenile Sooty Tern. I mainly included this one because it is a good example of how birds turn up dead at just the wrong time. We are going to press now with our Field Guide to Beached Birds of the Southeastern United States, and this bird, with the fine pics taken by my friend Emily, waited to die until it could not possibly be included in that volume. Next edition, to be sure. These photos also demonstrate the proper dead bird photo technique–spread wings, head in profile. There are few species this might be confused with, but the field marks that I find of particular use when, say, only the wings are present, are those white spangles over the upper wing, and the contrasting whiteness of the underwing. Thanks to all for playing!