Seriously, I think this Black-Headed Gull (Chroicoephalus ridibundus) just wanted to show off. As well as giving his tonsils an airing he was also emitting an ear piercing scream, he was sat in the local park waiting to be fed. I know he has not got a Black head, they lose the colour over the winter, just keeping the black spot behind the eye. Come the Spring he will have a lovely Black Hood.
@darylo He sure did. Thanks Daryl.