Tuesday, 3 November 2020

White Gulls

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...

8 comments:

  1. A Leucistic Herring Gull has caused similar problems in Northumberland since summer...

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    1. Ha! I guess it's true that while they might be interesting they are also a bit of a nuisance! 😄

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  2. Very nicely dealt with, buddy. And I particularly like the way you snuck in that melanistic white winger in the final pic. Iceland due to wing length?

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  3. A lot of 'jizz' and 'white stuff' for so early in the day but interesting for all that.

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    1. Thank you Dave. Of course, in a birding context 'jizz' has a U-certificate and is appropriate for any time of day... :0)

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  4. Thinking about this bird more, it was present at SBR again yesterday, the long wing projection and slightly daintier look could suggest a leucistic LBB Gull rather than Herring?

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    1. I guess it's possible Tim. The Axe bird depicted above raised the same question. However, certainly as far as the Axe goes, LBBG is pretty much migratory, and far less likely to hang around/reappear than HG. Also, on one occasion the Axe bird was chased about by a large male HG with obvious intentions. Structurally, HG is massively variable. Personally I would say the balance of probability is against LBB, but that's just my opinion.

      Once again, grateful thanks for letting me use the photos! :)

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