To me it's pretty obvious that it's not an GBBGull. As Ruud have pointed out I allso beleave it's a mix with tatus. If you look away from the fact that it has been ringed as a GBBG, what would you have id'ed it as? As the colony are a mix of GBBGulls, tatus and LBBGulls, can a hybrid with LBBG be ru...