Although I was the first one who dared to ID the bird as a female first-winter
Slaty-backed Gull (see old posting below), I still would NOT say that we
'SETTLED' on a definite ID.
We clearly ruled out Thayer's Gull, American Herring Gull (see below), the
fuscus complex including Heuglin's Gull (heuglini and taimyrensis), Eurasian
Herring Gull, and most of the "yellow-legged gull complex". Moreover, as I
indicated a week ago, tail and primary patterns speak against Mongolian and
Steppe Gull.
And also Vega doesn't fit 100%. But - although it was my favorite - does
Slaty-back fit 100%? No, it looks good for a Slaty-back, but apparently not
100%! Look at all the divergent comments from experts from all over the world!
I think, the final ID at this point should be "possible Slaty-back".
Two years ago, two friends of mine (Eric Pilotte and Simon Thompson) and I
found two interesting subadult gulls in Barrow, Alaska. We nailed them down to
Heuglin's Gull (heuglini or taimyrensis) but were never able to 100% rule out
Lesser Black-backed Gull - so we decided to call them possible Heuglin's Gulls.
(of course, we had plenty of Vega and Slaty-backs there...)
Cheers,
Nikolas
Here my posting from a week ago:
Jon, Mike, Richard et al.,
Yesterday when I saw the first two pictures of the perched gull my "gut
feeling" immediately ruled out Thayer's and I indeed thought of Vega Gull,
barabensis-Steppe Gull, mongolicus-Steppe Gull or Slaty-backed Gull.
Now I've seen Richard Baxter's flight shots. The large pale window in the
primaries indeed immediately rules out the fuscus complex including Heuglin's
Gull (heuglini and taimyrensis), but it is in my opinion also way too large for
so-called "Herring Gull Complex" (Eurasian Herring Gull, American Herring Gull
and Vega Gull) and for the "Yellow-legged Gull group", including mongolicus and
barabensis. The pale window (formed by the pale inner webs of the primaries vs.
dark blackish brown outer webs and tips) in the Cooktown bird actually reaches
P9!
The pattern of the primaries (which looks good for Slaty-backed, but also for
Thayer's), the spotted/barred upper and under tail coverts with broader white
than dark bars (looks better for Slaty-backed Gull than for Thayer's and also
rules out American Herring Gull), the almost solid dark blackish brown tail
(which speaks against Eurasian Herring Gull and the "Yellow-legged Gull
complex", but also against Vega Gull), the bleached scapulars (which in my
opinion don't necessarily rule out a first-winter Slaty-backed Gull), and the
bill shape with a relatively flat gonydeal angle (which would rule out a male
Slaty-backed Gull) makes me think of a female first winter Slaty-backed Gull.
I am looking forward to more comments that hopefully will finally lead to a
positive ID of this interesting bird!
Nikolas
and another one:
However, typically first-cycle American HG appear very dark: the underparts of
a first-cycle American HG are typically uniformly brown and not as splotchy as
in the Cooktown bird. Also the upperparts are typically darker due to narrower
pale fringes of mantle feathers and scapulars. The most important field mark
are the under tail coverts which are densely barred with the dark proportion of
ore than 50% leading to the impression of dark brown undertail coverts with
very narrow white barring (and not white undertail coverts with some brown
spotches and bars as in the Cooktown bird). This pattern is somewhat
reminiscent on that of a juvenile Pomarine Skua! Similar 'rules' apply for the
upper tail coverts. The tail of a first-cycle American HG should typically be
totally dark brownish black, but there are many birds
with barring at the bases of the outer three rectrices. Another interesting
fact is that typicalley American Herring Gulls still have juv. mantle feathers
and scaps in February.
Cheers,
Nikolas
P.S. Two friends of mine (Martin Gottschling and Andreas Buchheim) and I just
had a paper (unfortunately in German) accepted for publication in Limicola. I
spent the last five years in the US and documented a lot of American Herring
Gulls of various populations, whereas my friends did the same in Europe with
European Herring Gulls.
----------------
Nikolas Haass
Sydney, NSW
----- Original Message ----
From: Tony Russell <>
To: Mike Carter <>; BIRDING-AUS
<>
Sent: Saturday, February 23, 2008 2:29:38 PM
Subject: Cooktown Slaty-backed Gull happily post sitting today
So, have we settled on Slaty-backed now ? Going Tuesday.
-----Original Message-----
From:
On Behalf Of Mike Carter
Sent: Saturday, February 23, 2008 10:45 AM
To: BIRDING-AUS
Subject: Cooktown Slaty-backed Gull happily post sitting
today
The floods have subsided, fine weather has returned to Cooktown and the
Slaty-backed Gull is extant on her post. Colin Judkins took 3 hours 40
minutes to drive there from Cairns this morning.
Notice David (Taylor), it is a 'she' not a 'he'!
Mike Carter
30 Canadian Bay Road
Mount Eliza VIC 3930
Tel (03) 9787 7136
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