Quiz #313 (2009-3-08) Answer

Click the picture for a larger view.

Answer by Tony Leukering

Mark Peterson took this week's quiz photo at Fountain Creek Regional Park, El Paso Co., CO, 27 August 2008 and it was obvious to this week's respondents that it was of a cormorant and a youngster at that. Because the face pattern is not crisp and the bird's plumage is not blackish, our bird is almost certainly a juvenile. The presence of a large and bright orange gular area should bring us to a dichotomy that is often much more difficult than most field guides suggest: Double-crested vs. Neotropic. Even though some Great Cormorants can have an orange gular area, the bird's lack of white on the belly rules out that species.

Typical juveniles of both species are fairly readily identified correctly, but there is an unfortunate number of 'tweeners that demand very careful scrutiny. This fact is not illustrated any better than with the following story.

When I started contemplating writing the answer for this week's quiz, I looked at the picture again and was suddenly not so certain that I had correctly IDed the beast. So, I sent a request to four of North America's best birders (1 west coastal, 2 east coastal, and 1 interior) asking them to let me know what they thought the correct ID was. I don't know why I didn't send that request to an odd number of experts, because I should have expected what I got: a tie score, 2 for Double-crested, 2 for Neotropic. However, after further discussion, they were unanimous in their ID, so I shall continue.

Most juvenile Double-cresteds are more extensively white below than the quiz bird while most Neotropics are less white. Unfortunately, it's difficult to be certain of the extent of white, as the photo is overexposed and the white that is present may be an illusion caused by that overexposure. So, we'll have to check other features. Additionally, Double-crested is more variable in plumage as juveniles than is appreciated by most birders, as is illustrated by two darker-breasted cormorants illustrated on my flickr site, one from

California

and one from

New Jersey.

We can be certain that both of those cormorants are juveniles, as their remiges (wing flight feathers) are all of the same generation and there is only one time when that is true of cormorants, when they're in juvenal plumage. This is because cormorants exhibit staffelmauser, a molt strategy that limits the number of large, energy-expensive feathers that they replace in any one molt (see the paper on molt, figure 6, by Peter Pyle), causing adults to always have at least two ages of remiges.

So, let's continue.

Tail length is a good indicator of species in this duo, but the angle of the picture makes it a bit tricky to be certain of our bird's tail length. It does not look particularly long to me, but I am not willing to base my ID entirely on that feature in this bird. That leaves us only head pattern on which to base an ID. Even juvenile Double-cresteds typically sport a supraloral strip of bare orange facial skin that our quiz bird lacks. Additionally, there is a distinct white band behind the orange gular skin. These two features point directly at Neotropic Cormorant and, generally, away from Double-crested. Unfortunately, the latter of these two characters is often present on juvenile and immature Double-cresteds, but the lack of supraloral orange is considered by many to be diagnostic: Double-cresteds always have it and Neotropics always lack it.

Of course, this is biology we're talking about, and biology is rarely that neat. Colorado birders have a slight advantage in this in that I wrote a piece for Colorado Birds on this duo, highlighting a picture taken by Michael O'Brien of a Neotropic Cormorant that exhibited an orange supraloral band (Leukering, T. 2008. Neotropic Cormorant (In the scope column). Colorado Birds 42:226-228.). And, if Neotropic can sport such, surely some Double-cresteds can lack that feature. If this is true, what about gular area shape characters?

Though I've been wrong often enough before now, I believe that our most certain road to correct ID of this quiz bird and the two species, in general, is through careful analysis of the shape and size of the bare skin in the gular area and the shape and orientation of the meeting of that area with the feathering posterior to it. In Neotropic, the area of bare skin is small and the meeting with the feathering behind it angles forward from the gape at about 135 degrees. In Double-crested, the orange gular area is large and the meeting with feathering is nearly vertical (or 180 degrees).

So, despite our bird lacking a supraloral patch of orange and its fairly dark neck, this week's quiz bird is a Double-crested Cormorant. The photographer believes that it is the indivdual that was reported from the site as a Neotropic Cormorant, a review species in Colorado, and one can certainly see from Mark's picture how that mistake could be made.

Incorrect species provided as answers:
Neotropic Cormorant - 7
Great Cormorant - 3

The 8 of 18 providing the correct answer:
Nick Komar
Tyler Bell
George Cresswell
Victor Germain
Al Guarente
Margie Joy
Mark Gilsdorf
Barbara Deneen

Answer: Double-crested Cormorant

Quiz #312 (2009-3-07) Answer

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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
flickr.com/photos/tony_leukering/1994650566/.
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