Monday, March 22, 2010

Quiz #341 (2010-1-12) Solution

Click the picture for a larger view.

Answer by Judi Owens and Tony Leukering

Judi Owens, a fairly new player of the Mr. Bill Mystery Quiz, provided a thorough answer to this week's quiz. Her answer just goes to show what focused study of available materials can do to enable figuring out gulls -- they're really not THAT hard! Since Judi's answer covered all the bases, I'll let her take it away.

"It is a gull. :( I don't do gulls. But I am going to make this a learning experience (and embarrass myself further) by attempting it.

"First I will describe the bird. The mantle; scapulars; and the lesser, median, and greater coverts are all the same shade of medium gray. Primaries 6-10 are blackish with bold white tips. The tail is white. The head is heavily streaked with brown from the base of the bill to the hindneck. There is no other visible brown on the individual. The iris appears golden brown and the orbital ring is red. The bill is yellow with a straight culmen and downward curved maxillary tip. The legs are pink.

"I am not confident calling this a large or medium gull with a large or small bill without much more experience on which to base these comparisons. However, in your previous quizzes, you lend some clues that are not as easy to glean from Sibley and Howell/Dunn. In quiz 335, you call that bird's bill 'substantial;' this bird has a bill that is less substantial, but not small. Also learning from your earlier Mr. Bill Mystery Quiz #335, the bird in that photo has a mantle that is close to the color of the mantle of this week's quiz bird. So, I think that I will be in the ballpark if I assume the mantle shade of this week's bird to be in the 6-7 range and not outside the 5-9 range.

"I note that there is very little, if any, brown on the bird other than on the head, so I am going to assume that we are dealing with an adult or nearly-adult bird. This is good! I don't have to give up yet.

"OK, now I am catching on! The color [red gonydeal spot] and size of the bill allows us to eliminate the small and medium-sized gulls, leaving us with the large white-headed gulls. In Quiz #335. I learned about 'skirts' and this bird lacks such, thus saving me from submitting Glaucous-Winged X Western as a wrong answer. So, I am not going to consider Slaty-backed, Glaucous-winged, Western, or Yellow-footed, as these are skirted gulls.

"Looking at large white-headed gulls with pink legs and lacking skirts, I hope that these do not change with breeding or age and send me down the wrong road. The contenders, then, are: Iceland, Glaucous, Thayer's, and Herring. Iceland and Glaucous are lighter than this bird and have little to no black on the wingtips. That leaves Thayer's and Herring to consider.

"The following features favor Thayer's Gull over Herring Gull:
-- deep pink rather than pale pink legs,

-- purplish-red orbital rim rather than a yellow orbital rim (Siberian Herrings may have a red orbital rim),

-- streaking at the base of the neck becomes smudgy rather than clear streaking as would be expected in Herring (but this may be an artifact of the focus),

-- bill color, as per Mr. Bill Mystery Quiz #203, looks two-toned, yellow at the tip (especially the distal portion of the maxilla) and more green near the base, and

-- wingtips with bold white tips on p6-p10.

"Unfortunately, the head shape appears flatter to me rather than round and would support Herring. This could be due to the photographic angle or my lack of experience, but I still think the head shape is more suggestive of Herring. I also find that shape is often a better predictor of species than is plumage (at times), so this is bothering me.

"Other distinguishing features include jet black wingtips of Herring Gull compared with slaty-black wingtips of Thayer Gull. I'm not convinced that I can make a determination of that feature from this photo.

"While quiz 203 states that the color and pattern of the underside of the 'far wingtip' separates Thayer's and Herring, the underside of the wingtip is not visible.

"Well, I know a lot more about gulls than I did a few hours ago."

Thanks, Judi!

A number of respondents noted that they thought the bird was a "classic Thayer's Gull" and I agree with them, though the eye is a bit on the pale side for such. However, as Thayer's eyes can reach even yellow, this bird's eye color does not bother me a bit. Unlike Judi, I would say that the bird's head is pretty round, not the distinctively flattened and sloped head typical of Herring Gull. Though we have no comparisons available, the bird's mantle still looks too pale for various Siberian forms of Herring Gull, even the ones named Vega Gull. Finally, I will reiterate Judi's point about the primary tips -- I can often pick Thayer's out of pods of gulls in Colorado because they have such large white tips.

One quiz to go in the quarterly competition and Aaron and Al are still tied with perfect scores. No pressure, guys!

Incorrect species provided as answers:
Yellow-legged Gull - 1
Herring Gull - 3
Herring x Thayer's Gull - 1

Congratulations to the 23 of 28 getting the quiz correct:
Thomas Hall
Peter Wilkinson
Marcel Such
Joel Such
Tom Wilberding
George Cresswell
Al Guarente
Kevin Kerr
William Velmala
Chuck Carlson
Peter Burke
Tyler Bell
Bryan Guarente
Aaron Brees
Andrea Smith-Guarente
Joe Bens
Chishun Kwong
Su Snyder
John Bissell
Judi Owens
Nick Komar
Chris Warren
Margaret Smith

Answer: Thayer's Gull