---------- Forwarded message ----------
Date: Thu, 22 Dec 1994 13:45:02 -0800 (PST)
From: Joe Morlan <jmorlan at slip-1.slip.net>
To: Dan Victor <dvictor at U.WASHINGTON.EDU>
Cc: Multiple recipients of list BIRDCHAT <BIRDCHAT at ARIZVM1.CCIT.ARIZONA.EDU>
Subject: Re: Hybrid Western x Glaucous-winged Gulls

On Thu, 22 Dec 1994, Dan Victor wrote:

> Forwarded from the Washington State (+B.C.) email group "tweeters"
> Dan Victor, Seattle, WA <dvictor at u.washington.edu>
> ==========================
>
> Date: Thu, 22 Dec 94 10:13:26 -0800
> From: Dennis Paulson <dpaulson at ups.edu>
> To: Multiple recipients of list <tweeters at u.washington.edu>
> Subject: Re: hybrid gulls

> I'm impressed that Chris Hill took the time to look that closely at a flock
> of over 100 "Larus vulgaris," and he touched on a subject that probably
> puzzles many.
>
> About this particular hybrid pair; my rule of thumb (or of alula) has been
> that the mantle color varies with the wingtip color, so that westerns, with
> their essentially black primaries, have a dark gray mantle (but in this
> region not so dark as many field guides show for western), and
> glaucous-wings, with their gray primaries, have a much paler gray mantle.
> This is pretty straightforward, but there is a caveat: in neither species
> is the mantle and primary color the same. It is rare to find a
> glaucous-wing with wingtips as light as its mantle, contrary to the
> illustration in the NGS field guide. I think this is most likely in summer,
> when the wingtips have faded more than the mantle and approach it in
> coloration, but even in a bunch of wings from AK (where there should be no
> western influence) from summer, there are obvious slightly darker gray
> spots at the wingtips corresponding to the black tips in other gull
> species. The more proximal parts of the primaries are about the same color
> as the mantle, whereas in westerns the entire wingtip, including the
> outermost primaries, is always darker than the mantle--*not* the same
> color.

This reminds me of the point I was trying to make in an earlier thread on
BirdChat in which I expressed the opinion that wingtips somewhat darker
than the mantle was not necessarily indicative of hybridization between
Western and Glaucous-winged gulls, but rather a matter of normal variation
within Glaucous-winged.

Chris Corben replied with the question "How can we test this?" which is
an excellent question. Looking at Glaucous-winged Gull specimens
collected well away from the range of Western or Herring Gulls would be
the best way to evaluate the extent of individual variation within
Glaucous-winged Gull. Dennis Paulson's observation that normal
Glaucous-wings from Alaska have wingtips darker than the mantle should
settle the question. His refinement that the bases of the wingtips
(anterior portion) are paler than the tip and are the same as the mantle
in Glaucous-winged Gull is an important caveat.

I also previously discussed the problem of immature hybrids in which I
expressed the opinion that the bird in the Nat. Geo. guide labeled a 1st
winter hybrid, would not strike me as odd and I would identify such a
bird in the field as a Glaucous-winged Gull. Real hybrids usually have
much darker wing-tips than that (including the bases).

> If one accepts the assumption that mantle color varies with wingtip color,
> then there shouldn't be hybrids with primaries much darker than the mantle.
> A typical hybrid should be rather inbetween--dark gray wingtips, mantle
> about intermediate between western and glaucous-wing. The birds that Neil
> Fergusson described as having "jet black wing-tips, but sporting a mantle
> of the same color as a glaucous-winged" by my definition could not be
> hybrid GWGU x WEGU. Mantle and wingtips do vary somewhat independently in
> hybrids, but not enough, in my opinion, to produce birds colored like this.
> There are no such birds among the many, many specimens of this group in
> the Slater and Burke museums. By my criteria these should be herring,
> Thayer's, or possibly herring x glaucous-winged hybrids. This last type is
> apparently not all that rare in this area and may be manifested by a bird
> that looks like a herring but has brown eyes! At least that's what we're
> calling such birds; if they're not HEGU x GWGU hybrids, something else is
> going on.

On the Oakland, California CBC on Sunday, I noticed a gull on the parking
lot at Golden Gate Fields race track which I called a Herring Gull at
first. It had a mantle the same as Glaucous-winged Gull, but much darker
(blackish or charcoal gray) wing-tips including the bases. Closer
approach revealed an all dark eye, eliminating Herring Gull. The
underwing tips appeared pale and so the next logical choice was
Thayer's. Unfortunately this gull was about the same size as a male
Glaucous-winged Gull and had a large bill. We agreed the wing-tips were
much too dark for a pure Glaucous-winged, but other than wing-tip color
there was nothing wrong with the bird for Glaucous-winged.

We ended up reporting it as a Western X Glaucous-winged hybrid, which
satisfied me at the time. However if Dennis' observation above is
correct, it might have been a Glaucous-winged X Herring.

[deletions]

> Like Thayer's, glaucous-wings and westerns vary in eye color from dark
> brown to light brown, even yellowish. Some of this is probably due to
> hybridization (westerns tend to have paler eyes than glaucous-wings). A
> good mark for "typical" western is a white head retained through the
> winter. I don't know if the fact that so many of our birds that look as
> dark as typical westerns have smudgy heads in winter indicates more
> hybridization than we realize or just variation in this population. It
> really seems as if there is a cline from glaucous-wings (which get darker
> to the south) to westerns (which also get darker to the south), but there
> *is* a break between paler and darker populations in WA, and hybrids are
> still a minority on the outer coast where the two come together, so there
> isn't complete interbreeding by any means.

I have never seen a Glaucous-winged Gull with a clear yellow eye, like a
Herring, but certainly agree that the eye color of Thayer's is quite
variable. The one Glaucous-winged that I have seen that did have a
yellow eye, we finally identified as Herring X Glaucous-winged, but it
had some black spotting mixed with gray spotting on the wing-tip.

I have often wondered about dusky head shading on Western Gulls in
winter. When I look at those closely it usually turns out that they are
either 1) not adult or 2) not really Western Gulls. They often show
other anomalies (especially pale underwings) suggesting hybridization
with Glaucous-winged.

[deletions]

> Well, only one more comment. I wish I could add these essays to my list of
> publications! I think a lot of people are doing a lot of their writing on
> e-mail now, at least some of it of lasting value, but destined to remain in
> the memory banks of main frames rather than be out on the printed page and
> accessible to everyone. I guess it's just another one of our many class
> systems. There are ways to search for old e-mail messages, and most
> bulletin boards are archiving them, but I wonder how much will actually be
> stored over the years. And just think how much we write that *isn't* worth
> storing, yet it'll be there too.

I think some of these discussions could be reprinted as
"Point/Counterpoint" in _BIRDING_.

>
> Dennis Paulson phone: (206) 756-3798
> Slater Museum of Natural History fax: (206) 756-3352
> University of Puget Sound e-mail: dpaulson at ups.edu
> Tacoma, WA 98416
>

Joe Morlan
Albany, CA