Date: 10/30/18 2:15 pm
From: Lars Norgren <larspernorgren...>
Subject: [obol] Gulls on the rocks demystified
Ed McVicker has provided a lovely photo that reminds me of the bird books
of my parents' era, or a diorama at the American Museum of Natural History.
The adult gulls portrayed in field guides are predominately in alternate,
what l grew up with as "breeding", plumage. But only one species breeds on
most of our coast. That is the Western Gull, J in Ed's photo. Note the
gleaming white head. All the other birds in the picture are hooded to
various degrees, in their winter plumage. Is this called "basic" in gulls?
A lot of them only have it for four months. Western Gulls never acquire the
winter hood. They wear their glad rags the year round. Likewise the bright
yellow bill, almost orange at times, remains bright throughout the winter,
while the other pink-footed gulls tend to get paler beaks in the off
season. In combination with its white head, the Western has a significantly
darker mantle than all the other routine species. Compare the folded wings
and back feathers on J to all the other gulls in the photo. No other is
charcoal gray. A final very helpful field mark is attenuation. How far out
beyond the tip of the tail do the folded primaries go?
On this Western we see pure black primaries with three apical spots
visible. One apical spot even with the tail tip, one beyond. This bird has
a relatively blunt silhouette at the back end. The bird above it,H, also
has black primaries,but 4 apical spots are visible, 3 of them beyond the
tail tip. It is a highly attenuated gull. Think of bubblegum being
stretched to its limit from between the clenched teeth of an indolent
scholar. Now check out the attenuation of the other gulls in this picture.
B matches H ( although only 3 apical spots are clearly visible because the
outer two merge) and another such bird is hiding unlabeled behind C. I was
so intent on primary projection at first that I didn't notice the dirty
yellow feet on all these highly attenuated gulls. They are California
Gulls. They average about 700 grams while the Western and all the other
pinkfoots in the picture are closer to 1000g. If lighting were more
favorable the mantles of these Calgulls would appear lighter than the
Western but darker than the other gulls. As it is they are facing into a
southwest wind with the westering sun behind them. We are seeing the shady
sides of the gulls, and the gray tones are deceptive.
"A" is a Herring Gull, but its mantle looks deceptively dark. This is
the " silver gull" to science(Larus argentatus) and many European languages
other than English."F" above it shows a somewhat paler, more typical mantle
tone for Herring Gull. In favorable light the mantle of a Herring Gull
looks cooler, perhaps bluer, than gray in our other gulls. At a glance A
could be mistaken for an "Olympic Gull". The darkish mantle is accompanied
by low attenuation. But A isn't finished with primary molt. P10, the
outermost primary, is still growing. Look closely and you will see two
apical spots merging at the very tip of the folded wings. This situation is
more evident in E, which appears to be further behind in molt and show no
primary extension beyond a single white feather tip. D shows the
attenuation typical of Herring Gulls. It is in its second calendar year
plumage. The primaries are not black, but more like dark roasted coffee
beans. The clincher in all these Herrings is the mean look to their head
profile. This is particularly pronounced in A. A high,rounded forehead
flattens out on top to abruptly end in a delicate crest at the top of its
nape. Compare with the more rounded profile of J. Herring gulls' head
silhouette tends to suggest a stereotyped hawk's head. The fierceness is
reinforced by a pale yellow eye under an overhanging eyebrow.
The beak of A looks heavy for a Herring. It's probably a large male
bird. D and E have more typically delicate beaks relative to J, the
Western. The two Calgulls have beaks that have faded to a dull yellow, but
retain the signature black and red spots on the gonys, that widened spot
near the end of the beak. They may well lose it during the winter. Fleshy
parts often lose much of their color outside breeding season.The two adult
Herrings show fairly organized streaking in their grey winter helmets. C is
a Glaucous-winged Gull. It will eventually develope a very grungy helmet,
often quite dark, devoid of striped pattern. C has very little attenuation,
like the Western J, and no black in the wingtips. A pure Glaucous-winged
has gray wingtips, no darker than its mantle. This species nests on the
Oregon coast in limited numbers from Yaquina Head northward. In winter
large numbers arrive from our north and are sometimes present in the
thousands around Tillamook, in the hundreds in metropolitan Portland and
the Willamette Valley.

 
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