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Date: Wed, 2 Mar 1994 14:44:12 -0800 (PST)
From: Dan Victor <dvictor at u.washington.edu>
Subject: Re: Siberian herring gulls
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Date: 02 Mar 94 14:18
From:Skip_Russell at beav.intersolv.com


Dennis Paulson wrote:
>
>The Burke Museum in Seattle has specimens of Siberian herring gulls, both
>from Siberia and Alaska. They look like smithsonianus herring gulls but are
>distinctly darker on the mantle. I have wondered if some of the "pale"
>Slaty-backed could possibly be L. a. vegae, or--not much more
>far-fetched--hybrids between vegae and slaty-backed. Vegae is certainly
>paler than northern western gulls, so it doesn't seem as if it should be
>mistaken for slaty-backed

I believe that's exactly what at least one of the birds was - a
vegae/Slaty-backed hybrid! Most of the Slaty-backeds here last winter
fit the description of pure Slaty-backed Gulls. They were very dark
mantled. At close range their mantle color was a dark slate, quite
obviously darker than even the darkest gray of our northern Western
Gulls (although at a distance they didn't always look that dark,
depending on light, angle, etc.). At one point, three of these birds
were together in the same flock. We studied them carefully, looking for
slight differences in head streaking or other plumage characteristics
that would enable us to distinguish them when we saw them alone. The
fact that we couldn't find any differences lends credence to the theory
that they probably came from the same breeding population.

There were others, however, that showed some variation. One in particular
was lighter mantled than the others. Those birders that were looking for
a Slaty-backed to add to their list, 'counted' it, but had a little bit of
a guilty conscience until they saw one of the dark ones. A couple of
other birds were intermediate. Also note that Slaty-backed and Herring
are almost identical in shape and jizz. I got to wondering [warning -
rampant speculation alert!] whether there might not be an intergrade zone,
somewhere near the east ends of the ranges of Slaty-backed and vegae,
where the two mix freely; and whether Slaty-backed might not show a cline
between the darkest backed birds at Lake Baikal to the west and the
lighter mantled birds farther east? I've heard that a significant number,
possibly even a majority, of Slaty-backed Gulls wintering in Japan show
some evidence of hybridization. If so, [wild, rampant speculation
alert!!] can the day when all northern Larus get lumped into "Sea Gull" be
far away? I hope that never happens.

> Question to Skip Russell--do you feel the gull concentrations near
>Portland have anything to do with the early spring smelt run on the
>Columbia River? That's what I had thought.

I'd imagine that the smelt run has a lot to do with the historical
wintering patterns of the northern gulls in Oregon, but I really don't
know for sure. I can say that we seem to get more birds than usual
(including Loons, diving ducks, etc.) in the Columbia during the smelt
run. We also seem to find the unusual gulls (and the largest
concentrations of the common gulls) along the rivers, and not at the
coast as might be expected. It's absurd how hard it can be to find
even a Thayer's at the coast sometimes, but they are always present in
the Portland city parks.

The more immediate factor influencing last winter's extravaganza
certainly, I believe, has to be the feed proceessing plant ("pellet
plant") on Sauvie Island. There was a huge supply of fat-rich food,
free for the taking. Enough to support even the ten thousand gulls that
were present at the time. Since the 'demise' of the pellet plant, it
appeared to me that the flocks of gulls arrived on schedule during the
winter, checked out the place, and then moved on, as evidenced by the
report of one or two Slaty-backs in our vicinity (Washinton side
of the Columbia) earlier in the winter.

Skip
--
Skip_Russell at beav.intersolv.com
Aloha, Oregon