Caspian Gull

Note the almost snow-white appearance to the underwing with a long white tip to P10 complemented by a large mirror on P9 (together forming a white roundel isolated at the wing tip by an arc of black across the outer primaries).Ê

The black region is itself quite restricted (importantly, it tapers right back to include a clear black bar on P5 - not visible in photo) and roughly echoes the rounded shape of the wing tip.Ê Put another way, the pale (whitish) primary bases look 'scooped out' against the black wing hand.Ê

Especially, note the distribution of black and white along the underside of the P10.Ê Effectively what you see in the picture is the broad inner web of P10 with a long white tip, a subterminal black bar and then a resumption of white running back along the remainder of the feather.Ê

For aÊ (clearer) comparable example, see a flight shot taken by Lars Jonsson of an adult Caspian Gull published in Alula (4:76 figure 3).