Wanstead patchwork: Part XXI (When is a Caspian Gull not a Caspian Gull?)

In the last few days I have studied 1st winter gulls more than ever before. Here is a 1st winter Caspian Gull:

Caspian Gull (Larus cachinnans) - PHOTO BY NICK CROFT

Caspian Gull (Larus cachinnans) – PHOTO BY NICK CROFT

It has been on the patch for a few days and several people have seen it and photographed it (see here and here ). When I first saw a photo of it, I doubted that it was a Caspian. The gonys angle on the bill looked too deep (although not so much in this photo), the eye mask was instantly reminiscent of the Yellow-legged Gulls I had recently seen in Ibiza, and it seemed to have an under-advanced moult when I compared it with my field guide drawings. But now, I can see how wrong I was.

Although I had been looking at a slightly different picture where the tertial feathers were not as clear, I can now see that this bird does have a relatively parallel bill, it has a clear ‘shawl’ of streaks on the neck around the otherwise white head, and it has a white-edged set of tertial feathers that are otherwise uniformly brown. In sum, it is a Caspian Gull.

Today, I was half-fooled by a 1st winter Herring Gull. It had a beautiful white-ish head (although in my photos this doesn’t seem quite as striking as in my mind’s eye), seemingly long legs, and an upright stance.

Not a Caspian Gull

Not a Caspian Gull

When it flew, it seemed quite pale under the wing:

Not a Caspian Gull

Not a Caspian Gull

But, it had one thing above all that made me want to believe it was a Caspian Gull: it looked different. It walked about, pecking at bits of rubbish alongside a couple of other Herring Gulls (not shown) that had darker heads and just looked more like proper Herring Gulls.

A couple of us followed it about and took photos of it in various different spots:

Not a Caspian Gull

Not a Caspian Gull

But (yes, another ‘but’), something was wrong. At the time, it wasn’t really careful observation that identified the problem areas, it just simply looked wrong. I just wasn’t happy ticking it off in my mind. Different, maybe; but Caspian… not so much. Now I am home, of course, I have had a chance to study the photos more and I can see how ‘wrong’ it was. The main thing is the tertial feathers, they are chequered instead of pure brown with a white edge like the first photo. Pale head maybe, but no clear streaking on the neck, and the bill is just not long or narrow enough. It was a Herring Gull all along.

Whilst there were plenty with dark heads that I didn’t photograph, as I walked around I saw other Herring Gulls with quite pale heads:

Herring Gull (Larus argentatus)

Herring Gull (Larus argentatus)

The one above has quite a round head, whereas the one that confused me was more sharply defined like a Caspian, but even so, this shows that I shouldn’t have been so obsessed with a single feature.

So, no patch or life tick for me, even though the real Caspian Gull was apparently out there today (I look forward to studying the photos of it carefully!) But I have probably learned more about Herring Gulls and Caspian Gulls than if I had seen a definite Caspian, ticked it, and moved on.

I had shown a couple of guys where the ‘Caspian (not Caspian)’ had flown to and was pointing it out by saying “it is just to the right of the Great Black-backed Gull” when one of them said, “are you sure that’s not a Lesser Black-backed Gull?” On that particular call, I am confident that it was indeed a ‘Great’, and not a ‘lesser’. Phew!

Great Black-backed Gull (Larus marinus)

Great Black-backed Gull (Larus marinus)

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