Monday, August 10, 2009

Quiz #312 (2009-3-07) Answer

Click the picture for a larger view.

Answer by Tony Leukering

All respondents got this week's quiz bird to the right genus and then they were perfect from there -- in that none of the world's five species of loons were lacking from the answers. The correct response was received from a plurality of respondents, but not a majority.

Starting with the bird being a loon, the important features to note are bill shape and size, head pattern, neck pattern, and pattern -- if any -- on the upperparts feathers. In fact, we'll start with the last item, as that will enable us to age the bird, a feature that could be quite helpful. There are fairly distinct pale edgings on those feathers, indicating that our bird is either an adult Red-throated Loon (which option is negated by our bird's head pattern) or is in its first plumage cycle and retains much (if not all) of its juvenal plumage; other adult loons are plainer-backed in basic plumage (and the bird is certainly not in alternate plumage!).

Moving up to the bill, a few respondents noted, either directly or through their estimation of the species, that the bill was quite large. However, note that for its length, the bill is quite thin (top to bottom) virtually throughout its length and comes to a fairly fine point and with no particular gonydeal angle. Yes, the bill is pale, but it's certainly not the typical bright yellow or creamy-yellow of Yellow-billed Loon and the aforementioned lack of a distinct gonydeal angle pretty well puts that species in the trash bin of possibilities.

The bird's face is mostly dark, with just a bit of white below the eye and before the auriculars. Also, note that the neck is heavily marked and, from this angle, lacks any white. These features do a pretty good job for us in eliminating the second-most-frequently-guessed species, Common Loon. In all non-alternate plumages, that species has a fairly sharp demarcation between the dark of the hindneck and the white of the foreneck, with the dark intruding into the white around mid-neck and the white intruding into the dark just above that.

The above eliminations leave us with the three smaller-billed loon species. Arctic Loon is actually much more like Common Loon in bill size and our bird doesn't seem to be holding its bill upraised, as is typical for the species, so let's tentatively rule that species out. With the head angle mentioned, we should also be able to rule out Red-throated, because that species also typically holds its head above horizontal. All that should leave Pacific Loon as the answer, right?

But, Pacific Loon (and Arctic Loon) should show strong demarcation between the dark of the hindneck and the white of the foreneck, which, as we noted above, our quiz bird lacks; there is no white on our bird's neck. Well, remember that we aged the bird as a juvenile. Could juvenile Pacific Loons have dark throats? Absolutely! Though not pictured all that well in many field guides, juvenile Pacific Loons can be quite similar in neck pattern to that of juvenile Red-throated Loons, as is illustrated by one of my pictures
So, our ID is confirmed.

Well, wait a minute, let's go back to the upperparts feathers. All loon species in juvenal plumage, have upperparts feathers entirely fringed with pale; all, that is, except for Red-throated, which has those edges restricted to short bars of pale on the sides of the feathers. In the four bigger loons, the feather pattern results in scalloping, in Red-throated, of elongated spotting. Our bird's upperparts are quite typical of those of Red-throated Loon and wrong for those of the other four loon species. This, then, agrees with our bird's very thin and quite pointed bill.

I took this picture of a juvenal Red-throated Loon at Sunset Beach, Cape May Co., NJ, on 8 February 2008. Recall that single pictures can often mislead us as to shape and posture -- as those features are rather fluid -- and the fact that the quiz bird's head is not elevated above the horizontal, while suggestive, is not at all definitive in assisting our identification attempt. I would suggest that the quiz bird is a male, in that its bill is on the long end and its head is on the square end for Red-throated Loon.

A number of those at the top of this quarter's leader board stumbled this week, leaving five in a tie at the top with 6 of 7 correct. For the annual competition, Aaron Brees has a whopping four-quiz lead over Andy Dettling and Robert McNab, with 25 of 33 correct.

One incorrect answer was received 2.5 hours after the deadline.

Incorrect species provided as answers:
Common Loon - 5
Yellow-billed Loon - 3
Pacific Loon - 2
Arctic Loon - 1

The 7 of 18 providing the correct answer:
Tyler Bell
Kevin Kerr
Mark Gilsdorf
Tara Nelson
Margie Joy
Al Guarente
Robert McNab

Answer: Red-throated Loon