Herring Gull (Larus argentatus argenteus / argentatus) - Portland Bill, Dorset, UK
Adult bird: photographed 27th May, 2017
On the morning of May 27th there was a flock of mainly large gulls, close onshore, at Portland Bill. Among them was this adult Herring Gull. It was noticable among the other birds, particularly while in flight, due to the large amount of white on p10 (both wings).
Inspection of these photos reveals a trace of black present on the inner edge of p10, near the tip, on the left wing at least. P9 shows a small white mirror. More interestingly, feather p5 has 'no black', except for a slither on both edges. Large, white wingtips were most obvious on the resting and swimming bird.
I have read that this combination of features can be shown by L.a. argentatus. The Portland gull's mantle was the same colour grey as the many L.a. argenteus birds present, but it is recorded that Denmark and the NW German L.a. argentatus can be similarly pale-mantled. re. http://www.gull-research.org/hg/HG5CY05.htm
I would be grateful for an opinion and comments from those with expertise and experience on this subject as to whether this bird is likely to be racial intergrade, or L.a. argentatus - as I have seen photos of a bird with what appears to exactly this upperwing pattern and colouration, (taken in the Netherlands), labelled as L.a.argentatus. on the gull-org website.