Gulls.

species: 
Herring Gull
scientific name: 
Larus argentatus
notes: 

Black ring with a white four alpha-numeric code, starting letters 'KU' or 'KX'.

note 1 :  

email sighting submit: 
colour-ring type: 
Legring : one, coded.
colour-ring colour (of the c-ring): 
Black (Niger) [N]
colour-ring code (of the c-ring): 
Four alpha-numeric code (4 letters/numbers).
countries where ringed: 
Russia.
First letter/number (of the c-ring): 
K