Posted by Phil Pickering (188.8.131.52) on August 16, 2000 at 14:38:01:
In Reply to: gull posted by Phil Pickering on August 13, 2000 at 08:45:26:
Since I'm undoubtedly guilty of trying to oversimplify a complex situation, and since I think these are two potentially important points, I'll risk adding further comments and more cautious rephrasing to attempt to add some clarity (hopefully Joe likes excessive speculating about his quizzes!)
To be precise, my wording should have been "the bill is among the last things to appear this mature in Glaucous-winged", not THE last, since GWs with adult-like bills and overall mature appearance sometimes do show traces of immaturity in their plumage, such as gray spots in the tail or brown in the tertials. However, to be very specific, I don't recall ever seeing a GW of this level of maturity, that is with the clean head and underparts, and mature-looking bill, scaps, and secondaries evident in this scan, that did not also show obviously grayish greater coverts - no matter how worn.
The situation seems to be different for Glaucous. Glaucous Gulls that are of this 'apparent' level of maturity - clean head, adult-like secondaries & bill etc., seem to often show real (not due to molt) whitish patchiness in the coverts, often particularly evident in the greater coverts. Perhaps due to this, it is my impression that the greater coverts of many near-adult Glaucous will fade/wear nearly or completely white by summer.
I may be wrong, but I'm interpreting the stringy, whitish things hanging over the secondaries on this gull as the annihilated remnants of whitish, immature greater coverts. Again, I have never seen this on a near-mature GW. This is based on summering and early fall GWs seen in Oregon (maybe the situation is different in Alaska where introgression with Western isn't such a factor?)
Unfortunately, I don't have the advanced knowledge of molt timing to know if there is an actual difference in molt sequences, or maturity of different plumage groups at different ages between the two species (does anybody?) It also may simply be that the 'last pre-adult' greater coverts (in particular) in GW are just more adult-like (grayish, maybe with remnant brownish tones) and less prone to wear, whereas in Glaucous they are relatively immature (and/or just more whitish) and much more susceptible to extreme wear. I may be misinterpreting the scan (maybe the gull is just in extreme molt or something), but in any case, I think whitish patchiness or pronounced clean-whitish wear in the coverts, particularly the greater coverts, is potentially a very good supporting mark for near-adult Glaucous vs. worn near-adult GW.
The black on the bill of a gull in the Western/GW complex can fade in a myriad different ways, but I have never noticed one with the exact pattern displayed by this gull - that is with two well-defined spots lying completely outward beyond the gonydeal point, on an (apparently) otherwise clean bill. The last black to fade on a GW seems to most typically be either inward from, or on both sides of the gonydeal point, or at the very least, obviously vertically level with it. The last black also most often tends to border the cutting edge, at least in part. When I stare at the bill in this scan it just seems to have the clean look of a fading Glaucous, that I personally find fairly distinctive.
I wanted to expand on one more point to which I had previously referred, because it may relate to the issue with the coverts - the large white wedge created by the pattern of white/adult-gray in the tertials of this gull may actually be diagnostic for Glaucous vs. GW at this age. I don't recall ever seeing a GW of this level of maturity that did not also have obvious brownish or adult-grayish tones much farther outward towards the tips of all the tertials - again, no matter how worn. Near-adult Glaucous Gulls, on the other hand, frequently show extensive clean-white in the tertials, as is evident here.
As Dave Fix and others have stated, the bill and head are clearly too large, and the forehead too flat for Iceland (at least as I know them from photos - I'd like to see one live someday!) I'm also now somewhat confident that the apparent problem with the shade of the mantle being too dark, and the mantle/primary contrast being too extreme for Glaucous is just an effect of the increased contrast in the photo. I suppose it could be argued that this gull is leucistic, or even a hybrid of some kind, but I don't see anything at all evident in the scan that would lead me in either of those directions. Glaucous "fits".
Hopefully, I'm not too far out in left field with this stuff. I've learned quite a bit about potential things to look at in the future thanks to thinking about this quiz gull. More gulls, Joe! (yeah, right)
Too much free time on my hands.
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