Monday, January 4, 2010
Click the picture for a larger view.
Answer by Tony Leukering, Thomas Hall, Bryan Guarente, and Margie Joy
The first quiz of a new year and felicitations to all in 2010!
I had a lot of help writing this week's solution, more so than usual, as tern ID is such a minefield. Many birders never really work hard enough at it to become proficient at tern ID, even some with otherwise exemplary skills. I, certainly, did not conduct due dilligence on the problem for the first 20 years of my birding career (and still don't feel perfectly comfortable), so I obviously cannot blame those that don't. However, terns have a different way of doing plumage and plumage change than most other bird species, a more complex way in most cases, so this is yet another reason, among many (!), for the difficulties folks encounter when attempting identification of such.
As this venue is not appropriate to delving deeply into the identification processes of tern ID, I suggest referring to sources that do a reasonable job, including Advanced Birding (by Kenn Kaufman) and Identification Guide to North American Birds, part II (by Peter Pyle; published by Slate Creek Press). I cannot stress too much the usefulness of the two Pyle guides to birders -- if you're interested in upgrading your skills, buy the books! Of course, once you do have Pyle in hand, read the chapter on molt in part II (our understanding has changed a fair bit since the publication of part I). Then, after you've pondered it for a bit, read it again. Then, consider how what you learn creates what you see in the field. Then, read it yet again. (The usual caveat applies: I have no financial interest in any books or other such materials recommended here.)
In terns, wingtip pattern is an incredibly important ID feature. So much so, that most species can be reliably identified from wingtip pattern alone. It is, however, not enough to simply note that the wingtip has black or it doesn't. One should determine how many primaries sport black, how black the black is, where -- precisely -- the black is on the individual primaries, and what the overall appearance the distribution of black makes. As many of this week's respondents made this very argument, I will let them do the job of running us through the ID. In fact, respondents provided a variety of tacks to get to the correct ID. Bryan Guarente also supplies the suggestion that I would otherwise have made to AGE THE BIRD! Margie Joy, though she provided a way through the morass of tern ID to get to the correct solution, also made a final comment that I thought particularly appropriate in this case which I quote below, but paraphrase here: start with the obvious bits and see where that takes you!
Thomas Hall wrote:
"One can quickly discern that this week's quiz bird is a tern, one with a snow-white belly and tail, eliminating about half the field of terns with many sporting a darker tail or grayish/black belly. Add to that the fact that the three outer primaries are black -- and only those three, one can eliminate most of the others which sport none or more and that the trailing edge on the underside of the wing is not dark leaves, in my opinion, Roseate and Least terns. A look at the forehead, just barely visible, gives a hint that it is white. The beak, a small and almost unnoticeable projection from the wing, is yellowish with a black tip (Least) and not black (Roseate), and that the feet are orange-yellowish (Least) and not reddish (Roseate). Therefore, I am left with only Least Tern."
Bryan Guarente wrote:
"I am going to try to do what you have desired us to learn to do for so long: age the bird first. This, thankfully, is an easy one to age. All terns with predominantly white upper wings have a juvenile plumage that contains some spotting, barring, streaking, or other form of patterning on mantle, underside, or upper wings aside from primaries or primary tips. The other age tip we have here is the full black cap and nape. With these indicators, we know that we have an adult bird.
"Now to the most important part of this discussion aside from age: bare-parts color. The bare parts of this bird are yellow (feet and beak (yellow with black tip)). There are only two ABA-occurring terns that have yellow bare parts: Least and Large-billed. One can easily rule out Large-billed Tern on many different features: bill size, mantle color, upper wing pattern, tail color, and number of black primaries. This leaves us with the smallest ABA-area tern, Least Tern.
"Another easy method to arrive at the correct conclusion is the number of black primaries. Least Tern is the only ABA-area tern that has three [and only three] completely black primaries in its adult plumage. Roseate Tern, the only other ABA-area tern with three [and only three] primaries with black on them, has just the tips black with the rest of these primaries a varying shade of gray. Although the methods are different, both, thankfully, lead to the same conclusion."
Margie Joy summarized:
"After all that, I think that I could have gone about this in another way, starting with [any one of] the most conspicuous features, like the long and narrow wings, the black wedge on the outer wings, or the distinctive bill and leg color. One or more of these characteristics would have brought me straight to Least Tern. That might have been a simpler process; who's to say!"
I took this picture of an adult Least Tern at Norbury's Landing, Villas, Cape May Co., NJ, on 25 May 2009.
Thanks to all those playing the Mr. Bill Mystery Quiz for keeping an enjoyable endeavor going (without you, there would be no quiz) and to this week's respondents, particularly to those quoted above, for enabling me to see how folks tackled the problem. It is a learning process for me to see where folks went right, or wrong, in their identification processes, and important, as it enables me to provide better written solutions to the various problems with which I task all of you. Here's to a great 2010 Mr. Bill year!
Incorrect species provided as answers:
Common Tern - 4
Forster's Tern - 2
Sandwich Tern - 1
Roseate Tern - 1
The 25 of 33 providing the correct answer:
Answer: Least Tern