Monday, September 13, 2010
Click on picture(s) for a larger view.
Answer by Margie Joy, Peter Wilkinson, and Tony Leukering
Margie Joy provided a fairly thorough answer, so the solution will start there.
"This week’s quiz bird, shown from below (so no upper markings) seems to be fairly small. It has a short, dark, somewhat-forked tail; dark head and throat with a fairly well-defined lower border; a pale band or collar that extends at least around the side of the neck; small, pointed bill; pale undersides with some erratic dark streaking extending onto the undertail coverts; and pointed wings. The underwing coverts are fairly dark, contrasting with slightly paler flight feathers. Because the underside of the bird is in shadow, it’s difficult to tell if the flight feathers are really this pale or if bright sunlight from behind makes it seem so. But there is at least some contrast.
"The pointed wings restrict the possibilities to swallows and a few flycatchers. The short tail eliminates the flycatchers, leaving me with the swallows (including martins) to consider. The wings of Cliff and Cave swallows are generally less pointed and the tails more square than those of the other swallows. Underwing coverts are pale, not dark like the quiz bird’s. I looked twice at Cliff Swallow, however, because of the dark head/throat, heavily streaked undertail coverts, and pale collar or neck band, but couldn’t make the other marks fit. Tail shape eliminates Barn Swallow.
"Swallows with white or pale throats in all plumages (Bank, Violet-green, Tree, and Bahama) can be eliminated. Northern Rough-winged Swallow can have a dusky (but not really dark or with a well-defined lower border) throat in some plumages, muted (not dark) streaking on the underparts, and the tail is square. That doesn’t quite fit so it’s out, too.
"That brings me to martins. There are several accidental martins on the ABA list, but none fits the quiz bird’s description, leaving me with Purple Martin. Sibley shows this kind of dark, erratic streaking (incoming dark adult feathers) on underparts on male Purple Martin in first summer plumage. The underwings, as shown in my field guides, are fairly dark overall but do show some contrast between flight feathers and darker coverts. So far, so good. I struggled a bit with the pale collar that I see on the quiz bird; it seems to have more contrast than that shown in field-guide illustrations. I will chalk that up to poor lighting and variability of individuals, and stay with Purple Martin as my answer."
I had meant to provide a caveat with the picture when I posted it indicating that the picture was taken in New Jersey and was not an ABA-area rarity. Fortunately, no one attempted one of the south-of-the border purple Progne martins, as they can be VERY difficult to separate from Purple. Additionally, Peter Wilkinson (our resident UK resident) provided his thoughts (and correct they were) about ageing and sexing the quiz bird.
"Anything but purple, of course, in this plumage. Interesting mo(u)lt limit, apparently suspended after the two innermost primaries. I haven't managed to track much down on this, but this is presumably a second calendar year male (one reference says adults start with the outermost secondary, which this clearly hasn't) but if this isn't going to finish the remaining primaries until it is back in its winter quarters, they are going to be 15+ months old."
I took this picture from the roof of my house in Villas, Cape May Co., NJ, on 20 August 2010, a time at which southbound Purple Martin migration has nearly completed at that latitude.
Incorrect species provided as answers:
Northern Rough-winged Swallow - 2
Cliff Swallow - 1
Congratulations to the 12 of 15 getting the quiz correct:
Answer: Purple Martin