Monday, November 28, 2011
Quiz #427 (2011-4-09) Solution
Click on picture(s) for a larger view.
Solution by Margie Joy and Tony Leukering
Margie Joy submitted a detailed answer that covers most of the bases, so we'll start with that.
"This week's quiz bird is a diving bird: grebe, loon, or duck. Since I can only see the bird's back and sides, I'm using the pattern on the back (very dark with crisp, randomly-arranged white speckles) to collect possibilities for the ID. Some grebes and diving ducks show an indistinct scaly pattern, but it's usually gray on gray, never the sparkly effect shown in the photo; I'm going right to loons.
"Several ABA-area loons show similar patterns to that of the quiz bird. Common and Yellow-billed loons in breeding plumage show bold black-and-white spots that are arranged in a tight checkered pattern. Non-breeders and juveniles of these two species show more indistinct patterns. Arctic and Pacific loons in breeding plumage show larger white patches in a barred pattern. Non-breeders of these two species show very indistinct patterns, while juveniles show small pale areas arranged in a distinctive scalloped pattern. That leaves Red-throated Loon. Non-breeding adults have the same sparkly pattern of white on dark gray or black that's shown on the quiz bird, so I'm guessing that this bird is a Red-throated Loon. To confirm my guess, I have found other marks that are good for Red-throated: white sides and speckled rump."
Thanks, Margie. To round out this solution, I have some disparate comments. All loons have black primaries and all have long wings such that they sport fairly extensive primary projection. Unfortunately, The Sibley Guide illustrates Red-throated with the wingtips obvious, but with those of the other loons not. Juveniles of all loons other than Red-throated have pale fringes to the scapulars and coverts forming a scalloped pattern to the upperparts on swimming birds. Red-throated Loon shows such in no plumage, with the pale marks on these feathers being restricted to well-defined spots or short bars on the interior of the feathers, not on the edge. Thus, the species, as Margie described it, looks sparkly. Like stars, which may be the cause of the species' specific epithet being stellata (meaning "starry").
Peter Wilkinson noted that he "hadn't realised how hard it can be to
distinguish from juv Northern Gannet." Indeed, the patterns on the scaps and coverts are remarkably similar. However, a Northern Gannet with that pattern on the wings would not have bright white sides. Finally, as noted by multiple respondents, the bird's legs are set well back on the body, unlike that for Northern Gannet.
I took this picture of a diving adult Red-throated Loon in basic plumage at the Cape May ferry terminal jetty, Cape May Co., NJ, on 18 February 2011.
Incorrect species provided as answers:
Common Loon - 1
Arctic Loon - 2
Congratulations to the 14 of 21 getting the quiz correct:
Answer: Red-throated Loon