If you are not interested in the finer details of large gull identification, you may as well quit this post now. Come back tomorrow, there is nothing for you here...
I arrived at the Wandle yesterday, and there were two Lesser Black-backed Gulls (LBB) on a post. As you may know, the LBB doesn't have a black back unless it is a fuscus fuscus so the more accurate name for it should be Lesser in-the-top-half-of-the-Kodak-gray-scale-chart-backed Gull. Anyway, it is not uncommon to find slightly different shades on the back of these gulls in this area, and I usually (and sensibly) dismiss them as individual differences, but there was a third bird yesterday that I thought was dark enough to warrant further investigation. You never know, I might find a continental intermedius on the patch. So I peered at it for a bit, took some photos, came to no conclusion at all and left.
Later that day, I pulled out the big scary gull book to see if I had a graellsii or an intermedius. It was all quite inconclusive as the shades of gray differ and there is a certain amount of interbreeding between the two subspecies. That was until I stumbled on the killer bit of ID factness.
And there it is, plain to see.
Once you know, you know. And I now know that the small mirror on P9 makes it an absolute certain graellsii. Excellent, it's just a common bird. Just like all the others on the patch.
See, I told you that you there was nothing else but gulls today.