Adult Summer - Cross Ness, London 7th July 2013 - Note the differences in size and plumage to the adult summer Black-headed Gulls. Bonaparte's Gull has a black not brown hood which emphasis the white eye-lids, slender black and not deep read bill. The upper-parts are also a tone greyer.
Adult Summer - Cross Ness, London 7th July 2013 - The primary pattern is distinct with white primaries with black limited to the feather tips creating a black trailing edge.
Boneparte's Gull - Larus philadelphia
Adult Winter - Eastbourne, East Sussex 8th February 2013 - Note the grey hind-neck that is characteristic of winter Bonaparte's Gulls and the large dark ear spot. The bill is especially slender and black and the legs are a subtle to bubble gum pink colour. The eye has black just in front adding to a rather cute facial expression.
Adult Winter - Eastbourne, East Sussex 8th February 2013 - Here the typical primary pattern can be clearly seen; lacks the dusky inner primaries on the underwing of Black-headed Gull