Lk. Estes gull (Beware: post contains gull jargon and minutiae and the thing is long)

[colorad...@aol.com]

Hi all:

At Nick's request, I have looked at the pix available of the bird that Scott Rashid found yesterday, and I must respectfully disagree with him about the bird's age and I am not sure that I agree with his species ID, at least in whole.  The pix available of the beast are not the best and any analysis is restricted in its definitiveness by the poor quality of the pix.  With that said, though, I will go ahead and discuss what look to me to be relevant features visible in these pix and referable to species ID.

1)  I don't feel that the beast is a "molt-retarded second-cycle" gull for a number of reasons that the bird's plumage makes fairly certain.  However, understanding my rationale requires a not-short-enough primer in gull plumage development and molting strategies, and here it is.

Most northern hemisphere-breeding four-year gull species (those scheduled to achieve adult plumage in their fourth year) conduct a preformative molt in fall/early winter, replacing juvenal head and (some) back plumage, but retaining nearly all juvenal wing plumage -- particularly the flight feathers -- and tail, along with some/much/most of the juvenal underparts feathering.  It has been shown that the high-arctic breeding species, specifically Thayer's and Iceland, conduct very little of that molt (if any), instead, having most of the plumage change in their first cycle being part of the first prealternate molt conducted in late winter/spring.  Thus, first-cycle Thayer's and Iceland gulls in Colorado in Nov-Dec (and usually much later) are still wholly in juvenal plumage.  They are fairly fresh and have brown heads concolorous with their brown necks and backs.  The Lake Estes gull does not match that appearance, having a whitish head with some odd gray patches.  Another key point is that juvenal primaries in large gulls are narrower and more-pointed than those of older ages of gulls, an excellent feature to assess the age of problematic individuals.

After completing their (fairly limited) prealternate molt in spring, they initiate their second prebasic molt in late spring/early summer and replace all feathers.  Such birds should then be intermediate in appearance between juv and adult -- having whitish head, at least some adult-type gray in the back, and variable amounts of brown underparts feathering.  Additionally, bill color changes in this time to be bicolored, often with the pale base being more extensive than the dark tip.  A scruffy, but reasonable example of such can be found here (http://www.flickr.com/photos/guylmonty/89023691/).

If the Lake Estes gull were to be a "molt-retarded second-cycle," it would have to have skipped its second prebasic molt.  However, such gulls are still wearing their juvenal flight feathers and much of their juvenal body plumage, particularly the wing coverts and scapulars, which are subject to extreme bleaching and wear, particularly when discussing Thayer's Gull, most of which winter on or near Pacific Ocean beachs, exposed to salt water and the abrading effects of sand and, for some/many, the bright, bleaching effects of southern California sun.  This bird is not at all bleached, and not at all worn.  In fact, the bird's outer primaries look to be juvenal primaries -- narrow, pointed -- and they are not at all worn, in fact, retaining the typical pale-fringed pattern of juvenal Thayer's Gull outer primaries.  This gull is not a second-cycle gull.

2) If the bird is a first-cycle gull, we have new problems.  As noted above and by Nick (http://www.pbase.com/quetzal/mysterygullad), this bird has a whitish head with some odd gray bits, a very sloped forehead, and very flat crown, all of which features are fine for a Glaucous-winged Gull in its first November.  Unfortunately, that bird's bill is WAAAY too small to belong to a Glaucous-winged Gull.  In fact, it's nearly perfect for a Thayer's Gull, but that head plumage is not that of a Thayer's Gull in its first November, and I've already shown that it cannot be an older Thayer's Gull.  Impasse.

I think that this is another gull that many birders consider anathema:  an unidentified and unidentifiable bird.  If I had to throw a possibility out there, I would consider Glaucous-winged x Thayer's Gull, as the bird seemingly has features of both species.  However, personally, I would call it "Interesting."  I would greatly appreciate Steve Mlodinow's thoughts on this beast, with his extensive experience in the Pacific Northwest, even if he thinks that I'm off my rocker.

Respectfully,

Tony

Tony Leukering
currently Smith Point, TX, but heading back to Villas, NJ, soon

[Nick Komar]

Many thanks to Tony for his in-depth and educational contribution to the discussion. I was not at all sure of my assessment of the wing molt on this “interesting” bird. I would support Tony’s assessment of the non-identifiable status of this immature gull. I’m sure this is not what the observers of this gull want to hear, but it is a great reminder that:

1. Gull ID is tough

2. Not all gulls (especially immatures) can be identified, partly due to extensive hybridization among large gulls

3. a high percentage of immature “white-winged” gulls that reach Colorado, many from the high arctic, are enigmatic and not identifiable with confidence. I have some photographic examples of at least 6 other enigmatic gulls in this category on my Mystery Gulls page at http://www.pbase.com/quetzal/mysterygulls.

 

If it were easy, it wouldn’t be as much fun! Thanks again, Tony.

 

Nick Komar

Fort Collins, CO

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