Thanks for the responses to my query about the large gull. Unlike the
previous query which elicited unanimous identification of a Pacific loon
in breeding plumage, responses in this case were divided, with three
saying western, two saying hybrid, and one saying glaucous-winged. The
latter is in fact impossible given the large black triangle at the tip
of the wing.

Where, however, does one draw the line between westerns and hybrids? To
the extent that one can rely on the Sibley field guide illustrations, a
solid dark triangle at the tip of the wing (as opposed to a streaked
one) would be definitive of a pure (or almost pure) western. The other
seemingly clear line of demarcation is an orange-yellow (as opposed to
pink) orbital ring. To inspect the orbital ring I zoom in close with my
telephoto and examine it from digital photographs.

Perhaps from an overabundance of caution, I have noticed a tendency on
the part of many local birders to automatically label any darker gull as
a glaucous-winged x western hybrid, forgetting that it is only possible
to have so many hybrids if there are a decent number of pure strain
westerns around. Otherwise there would be no way to hybridize!

I also have doubts about using depth of mantle color as a criterion.
There is a clinal variation among westerns in which the degree of gray
declines as one goes north. So a lesser amount of gray does not
necessarily mean it is not a western.

The other possibility is that western and glaucous-winged are really
just a single species with continuous clinal variation. There is always
something suspicious in biology about having too many hybrids.

While on the subject of taxonomy, isn't it peculiar that we are now told
to lump the easily distinguishable red and yellow-shafted flickers as a
single species, yet still told to distinguish the indistinguishable
northwestern crows from common crows?

Andrew

Here are two mystery gulls:
http://picasaweb.google.com/aareding/Wildlife

One of them has helpfully raised his wings. From the Sibley guide
illustrations, i am guessing western gull ... am i right?

Please click on "view largest photo" or "download largest photo" to get
closer to original size.

Thanks,

Andrew Reding
Port Townsend
aareding at gmail dot com