The top three images are of a juvenile gull currently present in Lissadell Bay in County Sligo (Ireland) (Michael Casey) whilst the remainder are of a juvenile gull that ranged widely throughout the London area and Home Counties in February-March of this year (Mike McKee).
Both birds are fairly similar and perhaps represent dark clades of juvenile GLAUCOUS-WINGED GULL plumage. On the other hand, perhaps there is North American Herring Gull influence and both birds may be unidentifiable hybrids. Whether or not such vagrants are identifiable to form is debateable, particularly when one realises the amount of convergence that is represented in northern California in winter.
