Herring Gull with thayeri wing pattern at Alnwickhill

A very brief visit up to the water treatment works at Alnwickhill yesterday produced this Herring Gull with a nice so-called thayeri type wing tip. That referes to the long white tongues running down the inner edges of the primaries and especially P9. This is a common wingtip pattern in Northern argentatus Herring Gulls though this bird appeared to be very much like the other local argenteus in all other respects - other than the iris speckling which gave a dark-eyed appearance to the bird. I photographed a similar bird in Dunbar in August of last year and there is a short thread in Gull-Research about that bird. Essentially I was interested to see whether this wing-tip pattern is found in argenteus Herring Gulls. The answer, based on research in Belguim and the Netherlands, appears to be that it is an uncommon pattern among pure argenteus and more common where intergrades between argenteus and argentatus occur. As for this bird, it could fit any of the above categories...