Subject: Hybrid Western x Glaucous-winged Gulls
Date: Dec 21 11:00:25 1994
From: Christopher Hill - cehill at u.washington.edu



On a recent Christmas Bird Count, my party was faced with distinguishing
intergrades from "pure types" in the Glaucous-winged-Western Gull
spectrum. Speaking only of adult gulls, for the present, I only used one
character to separate them: coloration of the primaries in the folded
wing. If the primaries were black, I called the birds Westerns, if the
primaries were the same shade of gray as the mantle, I called them
Glaucous-winged. If the primaries were darker gray than the mantle, I
called them intergrades. The putative Westerns and Glaucous-wings looked
pretty much homogeneous: once I ID'd them by primary color, I couldn't
see any difference in mantle color or anything else within the two
categories (although the intergrades did vary).

Using this approach, in a flock of 101 birds on the ocean beach, we
identified 84 Western Gulls and the rest were split between GWGs and
hybrids (there were only these two species in the flock). I forget
whether there were 6 GWGs and 11 hybrids or vice versa. Anyway, that was
a higher ratio of Westerns to GWGs and hybrids than is usual for that
count, which may not be surprising considering the Western's more coastal
tendencies combined with a strong (30mph) onshore breeze during the count
and the 24 hours preceeding the count. Needless to say, we had plenty of
Gull sp. on the count, but if primary color is reliable, in that flock of
gulls (at close range and sitting still) all seemed to be distinguishable
to type.

What do you longtime gull watchers think of that approach to separating
out the intergrades? Are there any other useful cues?

Also, just where exactly do you tend to find Herring Gulls around
Seattle (wow, I grew up in NY and I *NEVER* thought I'd be asking
directions to HGs)? And how about Thayer's and Glaucous?

Sorry if this is ground that has been trod before on tweeters. Feel free
to refer me to previous (archived) threads on gull ID

Chris Hill
Seattle, WA
cehill at u.washington.edu