Just in case you weren't bored enough of argy Herring Gulls last time, here's another post which to really send you to sleep. All of photos taken while seawatching at Whitburn Obs (Durham) today. Large gulls pass close inshore daily at this site, but particularly in northerlies. Adult argentatus are often easy to pick out (except a few borderline cases), as the crashing white waves really bring out the contrasts in their plumage. This results in the underwings giving an appearance vaguely reminiscent of adult Slaty-backed Gull. Ooof....now there's a thought. Immatures, particularly juvs/1st-winters, are however more difficult to separate from argenteus, and it's often difficult to be certain.