|The Rainham Slaty-backed Gull (above right) with Great Black-backed and argenteus Herring Gulls.|
If you compare Steve's latest images on his website with those here on my blog (also earlier posts), and photos by others, critical details of the bird's plumage, and especially the wing-tip pattern, can be seen to be the same. What is interesting is that these new clearer images show that the wing-tips are asymmetrically marked, with eg a small white spot on the inner web of P9 on the left wing which is not present on the right, and other minor differences. How common is this in large gulls? Does it suggest that the bird may not yet have developed a fully adult wing-tip pattern?
In the three weeks since the gull was first seen, it has also 'cleaned up' a little, especially around the head and bill. This would be expected in the passage of time towards spring, but as well as losing a little of the head streaking, the small dark markings on the bill have reduced, the bill is brighter towards the tip, and the legs are also a brighter, clearer pink. Even the eye now looks subtly more yellow, though this could partly be related to the brighter conditions in which it was photographed. Taken together, though, perhaps these characters suggest the bird is a near-adult rather than an adult, and help explain some of the points of concern about its appearance ...
Doubtless it will be looked for again today, but note that there is no public access whatsoever to Pitsea tip. To quote Steve on BirdForum: "The only options for looking for this bird are as [follows]: Wat Tyler Country Park main scrape viewable from hide, Bowers Gifford Marshes (most large gulls are going here as only a short flight from the tip) but is not accessible due to work being undertaken by the RSPB, and Vange Wick which can be either scanned distantly from Wat Tyler or by taking a very long walk out from the A127, many thousands of birds gather here though. The tip itself is strictly out of bounds and they are hot on access at the security gate."
Good luck to those who try. In the meantime, on today's to-do list is finalising the story on the bird for the next issue of Birdwatch, which goes to press this evening. It will include previously unseen images (including the best I managed to get of the bird) and further discussion of the ID.