A couple of months back I found this odd looking LBB gull at Oxenhope which stood out with the bright white upper wing patches, something I had,nt come across before.
Today I saw a similar bird at Ogden but with less white markings.
I asked if anyone else had come across this with no response so its obviously not a common sighting.
MC replied to say he thought it would be due to moulting.
Reading up tonight, ( Helm gulls ) it is caused by when the birds moult is at its peak and the primary moult reaches the mid primaries ,then the white patches are the white bases of the secondries showing through when the greater coverts are shed.
So if you see a white patched LBB from now you,ll know what its all about.
BS