Black Headed Gull

I snapped this little fellow on the river in Otley before the rains came today.
Its common name is a black headed gull, although for most of the year they have a white head like this one. I think it's just during the breeding season that their heads are black.
They are quite widespread inland in the UK and are not to be confused with seagulls.
I have often noticed that they seem to like standing on the edge of the wier keeping their toes cool in the running water.