Photo Bombing the Oystercatchers

The young Herring Gull didn't seem to care that it was surrounded by Oystercatchers (Shalders as they are known here). To be fair the Oystercatchers photo-bombed it as it was there first.
I noticed the difference in the bill colouring and read that a pure red bill is an adult bird while a black tip would signify either an adult that is already in winter colouring or a juvenile bird. While some birds over-winter here the bulk of them gradually depart as the year draws on. 
One pair I photographed a few years ago has rings on them from their winter in the Merseyside.