>I'm not impressed by whether it looks fierce or innocent, and I think
that Charlie Wright's comments that the bird has looked like both of
these subjective impressions ought to be taken seriously. I firmly
believe we should once and for all desist in using these impressions
as field marks, as I think they confuse more than enlighten. I have
photos of Thayer's and Mew Gulls with flat heads, as they're not
supposed to have. But why shouldn't they be able to flatten their
head feathers just as much as a Glaucous-winged Gull can? Their
skulls are not differently shaped than those of the other gulls.


I have to disagree with what Dennis wrote above. Jizz-type impressions
are only confusing because they are hard to convey to someone used
to looking at marks on a coarse level, so in that sense they are of
little use to the inexperienced. However to those who study them on
a finer level they can be extremely enlightening. For example on a fine
level Glaucous and Iceland on avg certainly do have discernably
different skull shapes (Glaucous typically being more elongated).
So while head shape can be confusing in one or a few photos due
to changing posture and feather position, if a bird can be studied
closely the differences usually are readily apparent. Also a "fierce"
facial expression is more than just flattened crown feathers - it is also
the
result of other subtle things such as eye position in the face, proportional
size of the eye vs the head, proportional size of the bill, etc that do vary
consistently among species and can be studied if one wishes to take
it to that fine of a level. To someone used to studying gulls that closely
an Iceland would not typically have the facial expression apparent
in Ruth's shots even with its crown feathers flattened. Certainly
impressions are more subjective and more likely to be misleading
at greater distance, but Ruth's shots are quite close and show the
bird in a wide range of postures, virtually all of which suggest
Glaucous over Iceland in terms of facial expression.

Rather than discouraging using "impressions" as marks I'd suggest
those who are really interested study what lies behind the impressions
so that they might be more usefully conveyed, since for an experienced
birder there is almost always physical substance to them.

>It really is too small to be a typical Glaucous Gull

Why specifically is it too small? There is known wide size overlap
between Glaucous and G-w, and in Ruth's shots the bird appears
nearly as bulky as what appears to be an avg size G-w hybrid. The
bill is virtually as wide at the base and as long as the G-w, and
Glaucous avg less gonydeal angle than G-w so that shouldn't be
an issue. Also again, the legs appear almost as long, and if anything
slightly thicker than the G-w, which would be strange for a Thayer's,
let alone an Iceland. Like Steve if it were far out of range I wouldn't
confidently call it a Glaucous either due to possibility of leucism
in Herring or other unknown, but it is in range, and at least in Ruth's
shots appears to be well within the known range of variation for
Glaucous in every way phenotypically. I see no reason at all to
suspect it isn't one - occam's razor and all that.

Cheers,

Phil