[obol] Hybrid Glaucous x Glaucous-winged Gulls (Invasion?)

[Cindy Ashy]

I've been taking a really close look at gulls lately and I'm wondering if we're
not only experiencing an "invasion" of Glaucous Gulls this winter but maybe
also an invasion of Glaucous x Glaucous-winged hybrids.

Maybe these Glaucous x Glaucous-winged hybrids are always here in fair numbers
(especially immatures in winter?) but it's just we're overlooking them. It is
easier to see the blending of traits between the Glaucous-winged and Westerns
with the obvious differences in pigment. I think perhaps the differences
between Glaucous and Glaucous-winged Gulls are more subtle....coupled with the
fact that this season most of us seem to be making a strict dichotomy based on
the presence or absence of a two-toned beak....I don't think it's this simple
however....and the subtleness of the differences definitely makes picking out
hybrids more difficult.

Last Saturday at the gull puddle, I saw a supposed first winter Glaucous-winged
Gull (not the one that was killed) with not even a hint of pink on the base of
the bill. HOWEVER, the shape of the beak was definitely shaped like a Glaucous
Gull....and it was so obvious to me I'm virtually 100% sure of this....but a
Glaucous-winged gull in every other way...a year ago I would not have noticed
the bill shape difference. The plummage was pale enough it could have been
either species but not as "patterned" as the Glaucous Gull....and for those who
care, the iris was as dark as the pupil. Several times recently I have seen
two-toned bills where the black was too extensive and/or too smudgy to be a
pure Glaucous Gull...and also many supposed first winter Glaucous-winged Gulls
with a hint of pale pink at the base of their bill. Then I've also been
studying the extensive variation in the plummage of first winter
Glaucous-winged Gulls...a very significant difference in "paleness" but more
importantly I think, a big difference in pattern, ranging from those that
basically lack a regular pattern entirely to those that show some pattern to
those that show a pattern very similar to what I've seen on the most patterned
first year Glaucous Gulls on the coast this winter. Bottomline, I think there
are A LOT of first year Glaucous x Glaucous-winged Gull hybrids out there this
year, most of which are likely being misindentified as pure Glaucous-winged
(because they're pale enough to not have Western Gull ancestry which is what
people seem to look for mostly). I would like to hear from some of the experts
on OBOL as to whether or not there have been Glaucous x Glaucous-winged hybrids
here in numbers in past winters/years.

If you look at the gulls long enough, the subtle differences start to become
more apparent. There is a definite difference in bill morphology. I think I was
noticing the difference before I could even put into words the difference. One
website describes the Glaucous Gull bill as, "long, parallel-sided" and I think
this is the trait that begins to jump out at you after a while. The website is:


http://www.chlorophonia.com/GLGUxGWGU_04082001.htm (excellent webpage!) 

...which shows some very detailed pics of Glaucous x Glaucous-winged hybrids
and points out some of the subtle traits to look for including also the flatter
crown and more gently sloping forehead on the Glaucous Gull (I'm beginning to
see this too). Linked from this is also a good page of Glaucous Gulls photos,
including a nice photo of 3 first cycle ones showing the range of plummage
pigment....and very good close-ups of that long parallel-sided bill:

http://www.chlorophonia.com/GLGU_11102000.htm

This Japanese website has some good pics of Glaucous-winged Gull hybrids as
well:

http://larus.hp.infoseek.co.jp/a_hybrid.html

...with particular attention to the "smudginess" between the black and pink on
the beak of hybrids...and how the black is more extensive on hybrids....and
some apparent Glaucous-winged Gull immatures (possible hybrids) showing a bit
of pink at the base of the bill.

Finally, I am wondering if these "southern invasions" are somehow triggered by
global warming. I remember a gull expert once telling me that the hybridization
zones are trending south in recent years....and hybridization more extensive. I
believe he was referring specifically to the Glaucous-winged x Western Gull
hybrid situation so I don't know if this applies to the Glaucous x
Glaucous-winged Gulls also but it is interesting to think about how global
warming may be affecting gull hybridization (gull evolution)....and if this is
also affecting the introgression between ducks species, owl species, and other
species that hybridize. I did also read that in Western Alaska, Glaucous x
Glaucous-winged hybrids can make up 50% of the gull population.

Cindy Ashy


 
____________________________________________________________________________________
Sucker-punch spam with award-winning protection. 
Try the free Yahoo! Mail Beta.
http://advision.webevents.yahoo.com/mailbeta/features_spam.html