A white-winged gull, ie Glaucous or Iceland, is a realistic
late-season prize for many birders. I managed to miss both last winter, but
around here they are pretty much annual. Locally I'm not sure I've seen either
species any earlier than February though, and for me Iceland Gulls have
outnumbered Glaucous at least three to one. However, an 'early'
white-winger is not unknown in the southwest; certainly I've seen
Iceland Gull on Scilly in mid-October, and I recall Steve finding a
smart juv Glaucous Gull on the Axe in November one year. So when Tim
Farr spotted a smallish white-winger out on the water at Sutton Bingham
Reservoir on October 15th he was pretty chuffed about getting an early
Iceland Gull. A few photos, courtesy Tim...
|
Exciting stuff! An early white-winger at Sutton Bingham
|
|
The bill pattern and dark eye point to 1cy Iceland Gull,
but...
|
At this point the bird flew to the causeway of the reservoir and perched up
among other gulls. It really was as white as it had looked out on the water, but Tim soon had doubts about the identification. He concluded that it was not
an Iceland Gull after all, but rather a leucistic version of something much
more common.
Here's what it looked like on the bank...
|
Not an Iceland Gull?
|
Tim posted some pics on Twitter, mentioning that he had written the bird off
as a leucistic job. However, that was not the end of the matter...
Some disagreed with Tim's diagnosis, suggesting that it looked
fine for a rather bleached, worn Iceland Gull. So I looked at it again...
My gut reaction had been the same as Tim's. Although I thought it promising on
the water, the photos on the deck portrayed a bird which to me just 'looked'
wrong. I too would have written it off. But now I tried to view it a
bit more critically. Had I got it wrong? Was this bird in fact an
Iceland Gull?
For me this bird nicely illustrates an aspect of gull-watching which has
struck me as becoming more and more evident in my own analysis of tricky
birds: the 'look' of a bird, its jizz. When you have sifted through thousands
and thousands of gulls in that search for something different you begin to
realise how much you rely on jizz for picking out the oddity. However, the
problem with jizz is its subjectivity. And because it is subjective it is open
to interpretation. In the case of this particular individual, some birders are
happy that it's an Iceland Gull, others quite the opposite. Logically
it has to be one or the other, so how do you get past jizz and make a
convincing case for its true identity?
I shall try...
Age
First up, the bicoloured bill and dark eye point to this being a first
calendar-year (1cy) bird. I would concede it might be older, but I highly doubt it.
Iceland Gull in its second calendar-year (2cy) would normally have a paler
iris and less black on the bill. A Herring Gull of that age might have
a similar bill to Tim's bird, but ditto a pale iris. So let's stick with the
age being 1cy.
Which means it's been out of the nest and independant for what, three months?
Four at the outside? A bleached, worn juv/1w Iceland Gull in late
winter I can accept, but mid-October?
Okay, suppose it is actually a 2cy bird. And suppose it
is actually an Iceland Gull. A 2cy Iceland Gull with an
atypical bill pattern and atypically dark iris...
If that is the case it will recently have completed its wing moult. The outer
primaries especially should be very fresh. Likewise the head and body moult
will have taken place through the summer months, so the bird should look
pretty neat and tidy by October. As we shall see, this bird is neither.
Structure
Structure-wise, Iceland Gulls are normally quite obvious. Smallish for
a large gull, with fairly short legs, a full body, long wings, and a
lightweight bill. Vaguely dove-like I suppose. I thought it might be helpful
to put together a collage of random Axe Estuary birds to give an overall idea
of what your average Iceland Gull looks like structurally...
|
Axe Iceland Gulls. At least 7 or 8 individuals are depicted
here.
|
There's a fair bit of variation evident among those birds, from the diminutive
little thing at bottom left, to the rather more butch individual bottom right.
And here's Tim's bird again...
|
Hmmm...
|
Personally I find it hard (okay, impossible!) to reconcile the appearance of
this individual with what Iceland Gulls normally look like structurally.
Doesn't the bill look hefty in this pose? Note too the scraggy plumage; it
doesn't look neat and tidy at all.
Finally...
Plumage
A white gull has no plumage characters, right? Thankfully that is not always
true, because white doesn't necessarily mean white. In the photo above you can
clearly see some darker markings on the scapulars, and possibly the head. So I
reduced the highlights on one of Tim's shots and got this...
|
No longer white
|
The scapulars are noticeably darker than the rest of the plumage, and what is
particularly helpful is the shape of those markings you can see. They are very obviously
anchor-shaped. Iceland Gulls typically do not have bold,
anchor-shaped markings in their scapulars. Take another look at the collage of
Axe birds and note what a normal Iceland Gull looks like. Those are
late-winter birds, but in October the patterns would have been just the same,
albeit fresher and more contrasting.
And note especially the central photo in the collage. Immediately right of the
Iceland Gull is a first-winter Herring Gull...with anchor-shaped
markings in its scaps.
I'll leave it there.
Personally I reckon Tim's analysis of this bird was spot on. It's a leucistic
1cy Herring Gull. Leucism leads to a bird's feathers being much less
robust than normal, which means they wear very quickly. So leucistic birds
often look rather scraggy, like this one.
Back in 2010 I got pretty excited about a white gull which had just dropped in
among the Coronation Corner gathering on the Axe. I was convinced I had an
Iceland Gull, and called over a fellow birder to point it out to him.
Rather quickly though, I had second thoughts...
|
Even in this apalling digiscoped effort it doesn't 'look' right, does
it?
|
A few days later it gave itself up properly by the tram sheds...
|
The pale eye points to 2nd-winter, but absolutely no plumage features at
all!
|
Subsequent events proved fairly conclusively that this bird was a leucistic
female Herring Gull, though there was initially some debate that it
might be a Lesser Black-backed. Crucially though, its build, its structure quite
clearly did not belong to an Iceland Gull. But that didn't prevent
regular reports of a 'white Iceland Gull' during its stay with us.
Which just goes to show that gulls are difficult. And in this case, even relatively
'easy' species like Iceland Gull are not always straightforward.
At the end of all this I will add a caveat...
I am not infallible and could be wrong. Perhaps Tim's white gull really is an
Iceland Gull. However, I've done the best I can to be objective about
the creature, so would take some persuading!
Finally, I wish you all the best with your winter gulling!
|
Ooh! A white-winger! Er...oh...wait a sec...
|