Gulls.

species: 
Great Black-backed Gull
scientific name: 
Larus marinus
notes: 

White ring with a black five alpha-numeric code, starting letter 'C'.

note 1 : up to 2014,a  total of 4 rings delivered since 1995.

note 2 :  

website sighting submit: 
Report form for Finnish ring recoveries.
email sighting submit: 
colour-ring type: 
Legring : one, coded.
colour-ring colour (of the c-ring): 
White [W]
colour-ring code (of the c-ring): 
Five alpha-numeric code (5 letters/numbers).
countries where ringed: 
Finland.
First letter/number (of the c-ring): 
C