[obol] Hybrid Gulls - Comments and Questions

[Cindy Ashy]

I stopped by Boiler Bay last Sat mid-day. There were several dozen
Glaucous-winged and Western Gulls. As they greeted me at the car in a cluster
and later lined up on the fence it made side by side comparisons very easy.
Judging from the color of the mantle and wings, on one end of the spectrum some
were obviously westerns and at the other end of the spectrum some were
obviously glaucous-winged. With them all lined up, especially on the fence, it
made picking out intermediate "hybrids" easy......or so I thought until I began
studying the head streaking situation....I didn't have time to do a precise
survey but this is pretty much what I found:

All the "for-sure" glaucous-wing gulls (on the extreme end of the color scale)
had streaked heads.

Although the intensity of it was quite variable (more variable than on the
extreme glaucous-wings), all the obvious intermediates (I presumed to be
hybrids) had head streaking.

All the "for-sure" westerns (on the extreme dark end of the scale) had white
heads with no streaking.

OK, so I'm thinking this head streaking thing is a dominant trait and is a sure
fire way to tell who's a hybrid in the winter....but then I took a look at
another group of gulls that had gathered on another fence.....uh oh...

Everything was the same as above EXCEPT the darkest most obvious "western gull"
did NOT have a white head and in fact had a more than average streaked head. So
much for an easy method dang-it!

So my concluding comment is that gulls are darn difficult to identify but in a
very interesting way that prompts one to ask all sorts of questions.

Is it possible to have a gw x w hybrid that is NOT intermediate in mantle/wing
color?

Could this just be variation in the timing of molting and not related to
hybridization? or even a molting malfunction? where the one obvious western
gull with the streaked head was lagging behind for some reason.

Could virtually all these guys have some degree of introgression? so when we're
looking at what we think is a really solid 100% western gull, maybe we're
really not. I vaguely remember a DNA study being mentioned once but can't
remember any of the details or even if it was for these particular gull
species.

I've read about dark feathers resisting wear better than light feathers and
white feathers being a structural color...and the structure of feathers with
prisms, air granules, and pigments....I scanned a paper on the molting patterns
in western gulls that would require much more of my time to fully
comprehend....but I'd what I'd really like is a simple explanation for the
possible selective advantages (if any - or is it just an artifact of molting)
of a streaked white head in the winter....and why in glaucous-winged and
usually not in westerns?

Cindy Ashy


 
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