The answer to my quiz photo is male Bobolink in breeding plumage (http://flic.kr/p/eJ1DrY). Perspective and comparative size made this a difficult identification. Only a few people answered correctly, and only one, Will Russell, noted the pale tips to the primaries as being a field mark. The bird is clearly long-winged, which Bobolinks are--they migrate back and forth to Argentina. I think wing shape threw many people, who considered swallows and swifts or goatsuckers. Those long wings are even vaguely like American Golden-Plover, which also flies as far. The spikey tail tips likely encouraged many to think Chimney Swift (31% submitted that), and that makes sense. The tail is too long for that species, however, among other things. Some did notice a little bit of white showing on the rump (a few pixels!), and that helped them clinch Bobolink while dismissing the wing tip pattern as wear or photo effect. In the end, I received guesses for ten different species in eight different families (only three passerine).
Maybe this was too difficult. To make up for it, what follows is an explantion of why I thought this quiz was a useful lesson.
This bird possibly could have been identified by shape alone, but the pale wing tips are, I think, unique to Alternate (breeding) plumage male Bobolink, which is otherwise so distinctive that these pale tips are never really necessary for identification, except in a view like our quiz bird. I have a couple of photos illustrating the wing tip pattern here http://flic.kr/p/eLoTdm and here http://flic.kr/p/ek1C5J.
No field guide or monograph that I know describes this character of male Bobolinks. The Birds of North America account, for example, says: "outermost primary (P10) edged on outer web with white, 2 adjacent primaries edged with maize yellow." That describes a different pattern, which they show, and not the pattern on the entire tip of the outer 3-5 primaries. The excellent monograph on the "New World Blackbirds" by Alvaro Jaramillo and Peter Burke likewise only mentions whitish "edges" to the primaries. Peter Burke's illustration does depict the gray wing tips, but it is otherwise not noted. Field guides sometimes mention the pale edging and ignore the wing tip, e.g. the Stokes guide, which otherwise has a glaringly obvious, and superb, photo illustrating the pattern! The only guide that will show it, I'm assured by the author, is David Sibley's upcoming revision to his field guide. I am looking forward to that.
I've thought about how odd this pattern is among birds, having pale tips to the primaries, which are so exposed to wear and bleaching. This isn't the same as the far more common trait of showing white at the base of the primaries (e.g., Black Vulture to Rose-breasted Grosbeak). The only other bird that I know, of off hand, with a similar pattern is a vagrant to North America, Northern Lapwing. The wing tip pattern on that species, however, is seen in all plumages to greater or lesser degree depending on age and sex. In the Bobolink, the pattern is, as far as I know, a feature only of the spring (Alternate) plumaged male. In fall after a complete molt, the males look like females. I have never seen this pale tip to the wing on the abundant overhead fall migrants. Both species do perform flight displays, however.
The Bobolink's molt is uncommon among birds, having two complete molts per year. Complete means all feathers, including wing and tail. Unlike most small passerines that grow a new set of primaries and tail feathers once per year and then "dress up" the body feathers for spring (think Blackpoll Warbler), the Bobolink has the ability to change its wing and tail pattern, as well as its body, for the spring fashion show. That is unusual. Kenn Kaufman had a great series called the "Practiced Eye" that was published in American Birds (now North American Birds), and he highlighted the changes the Blackpoll and Bobolink. His discussion and painting of the Bobolink, however, does not show the pale wing tip, even though he carefully notes how the Blackpoll's primaries are wear away pale edging by spring (http://sora.unm.edu/sites/default/files/journals/nab/v048n01/p00029-p00032.pdf).
The unique and striking pattern of the male Bobolink is probably one reason these pale tips have not received any attention. Who needs to look for them to know what the bird is! The other reason this might have been overlooked is that once prepared as a specimen, the closed wing makes it difficult to see the pattern.
Why would Bobolinks change their wing and tail patterns? (The tail tips also show pale spots not seen in fall plumage.) In their flight display, males beat their wings so rapidly that the wing tips seems to disappear. This makes them look short- and rounded-winged. Maybe that makes them seem stronger to females, which we know prefer males exhibiting longer duration display flights. These pale wing tips may be worth studying in terms of ageing Alternate plumage Bobolinks, which according Peter Pyle's detailed plumage guide cannot be done on current understanding. I don't think anyone has measured the breadth of these pale wing tips to see if it changes with age. Maybe older males have more (or less) dusty gray in the wing tip, and first year males might be identifiable by this method. The one study that attempted ageing criteria measured the width of black across the forehead, this becoming broader in older males (J. Nocera, North Am. Bird Bander 30: 1-5, 2005).
The plumage changes in the Bobolink were last a hot topic in the early 1890s when Frank Chapman described the two complete molts. His papers from 1890 and 1893, which includes a plate of the key specimen from sw. Brazil, can be seen free on SORA:
http://sora.unm.edu/sites/default/files/journals/auk/v007n02/p0120-p0124.pdf
http://sora.unm.edu/sites/default/files/journals/auk/v010n04/p0309-p0311.pdf
The most amazing birds are ever more amazing.
Louis Bevier
Fairfield
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