Re: Unidentified Gull

Alvaro Jaramillo


This gull is a real tricky one, for at least two reasons. But it is, in
my opinion, a worn and faded Glaucous-winged Gull. Most Glaucous-winged are
north of us at this season, and the whitish faded birds are something that
many of us do not get to see that often. However in May to July…they can
look extremely white. That is the first trick. The second trick is that this
bird shows a much more bicolored bill than is typical of a Glaucous-winged
Gull, but again this is more likely to be shown in the summer months for
first year birds. The reason is that that the sex hormones rise during this
time, even on young non-breeding birds, and this causes the bill to become a
bit more “adult like” if we can call it that. The bill will regress to a
less adult like state at the end of the summer, when the hormone levels go
down. The hormone level in immature birds is variable however, so it doesn’t
happen in every bird. I have been tracking bill colors in immature known age
(color banded) Western Gulls, and there is definitely a change between
summer and winter bills on youngsters in that species and I have no reason
to believe it doesn’t happen in other gulls as well.

Some additional points vs. Glaucous gulls: 1) This bird is not
white enough. If you look at the wingtips (primaries) they are creamy, not
white. Glaucous Gulls are white, absolutely white there, particularly on a
faded bird. 2) The black on the bill “bleeds” in towards the gape. This is
not shown by Glaucous Gulls which will have a cleanly set off black tip, a
straight-cut black tip essentially.



Alvaro Jaramillo

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Half Moon Bay, California

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From: SFBirds@... [mailto:SFBirds@...] On Behalf Of
Sent: Saturday, May 24, 2008 1:35 PM
To: SFBirds@...
Subject: [SFBirds] re: Unidentified Gull

I'm certainly not a Gull expert but I've been studying gulls in Joe
MOrlan's class (Wed. nights) and it certainly looks like a First Cycle
Glaucous Gull to me. The bi-colored bill, light pink legs, pretty
white primaries and overall lightness of the body are good. A first
cycle Iceland Gull would have an all black bill, besides a more
delicate looking one. According to the National Geo.field guide the
Glaucous Gull is 27". The Western Gull is only 25", so pretty close
but the Glaucous is pretty large. It could be a bleached something
else, who knows? Help Joe!
Martha Wessitsh

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