Common Tern

White ring with a 3 alpha-numeric code (on left tarsus) (to be read from bottom to top) and metal ring (on right tarsus).

note 1 : used codes are : letter/number/number OR letter/letter/number OR letter/number/letter.
NOT used letters are : B, D, G, I, O, U, Y while used letters are : A, C, E, F, H, J, K, L, N, P, S, T, V, X, Z.

note 2 : example of the 3-digit codes : A9A- A9Z, CAA-EZZ or LA1-LZ9 .

since 2016 also letter/letter/number rings have been used, starting letters L and E.

since 2019 E00-E99 have been used in Eemshaven.

in 2021 letter/letter/number rings wil start with A or C.

note 3 : from 2009 on, the middle digit stand for ringing year.
We used C0#, C1#, C2, (used in Limburg) , C4#, C5#. For the Eemshaven: E2#, E5#.

note 4 : some birds -starting letter 'C' are ringed belong the eastern part of the river the Maas in the Netherlands and the used codes are : C2x, C3x (where 'x' is a letter). 

note 5 :

White ring with a three alpha code, starting letter "X".

note 1 :

White ring with a black two alpha code.

note 1 :

Dark-green ring with a black three alpha code (on one leg) and metal ring (on other leg).

note 1 : starting letter "A", followed by two letters.
Used codes are : AAA-AZZ.

note 2 : birds ringed since 2022.

note 3 :

White flag with a black three alpha code.

note 1 : used letters as first letter : A, B, C, E, F ,H , J,K, L, M ,U, V, Y, Z.

note 2 :

Dark-blue ring with a white three numeric code (first number "4").

note 1 : used codes: 400 - 499.

note 2 : birds ringed in Cumbria and North Lancs, UK.

note 3 : 

Dark-blue ring with a white code :
a plus symbol before OR in the middle OR at the end of
a two alpha code OR a two alpha-numeric code OR a two numeric code.

note 1 : used codes are : +AA to +ZZ ; A+A to Z+Z ; AA+ to ZZ+

note 2 : used codes are : +A1 to +Z9, +1A to +9Z,  A+1 to Z+9, 1+A to 9+Z, A1+ to Z9+, 1A+ to 9Z+

note 3 : used codes are :  +00 to +99,  0+0 to 9+9, 00+ to 99+

note 4 :

Dark-green ring with a white code :
a plus symbol before OR in the middle OR at the end of
a two alpha code OR a two alpha-numeric code OR a two numeric code.

note 1 : used codes are : +AA to +ZZ ; A+A to Z+Z ; AA+ to ZZ+

note 2 : used codes are : +A1 to +Z9, +1A to +9Z,  A+1 to Z+9, 1+A to 9+Z, A1+ to Z9+, 1A+ to 9Z+

note 3 : used codes are :  +00 to +99,  0+0 to 9+9, 00+ to 99+

note 4 :

Black ring with a white code :
a plus symbol before OR in the middle OR at the end of
a two alpha code OR a two alpha-numeric code OR a two numeric code.

note 1 : used codes are : +AA to +ZZ ; A+A to Z+Z ; AA+ to ZZ+

note 2 : used codes are : +A1 to +Z9, +1A to +9Z,  A+1 to Z+9, 1+A to 9+Z, A1+ to Z9+, 1A+ to 9Z+

note 3 : used codes are :  +00 to +99,  0+0 to 9+9, 00+ to 99+

note 4 :

Red ring with a white code : a plus symbol before OR in the middle OR at the end of
a two alpha code OR a two alpha-numeric code OR a two numeric code.

note 1 : used codes are : +AA to +ZZ ; A+A to Z+Z ; AA+ to ZZ+

note 2 : used codes are : +A1 to +Z9, +1A to +9Z,  A+1 to Z+9, 1+A to 9+Z, A1+ to Z9+, 1A+ to 9Z+

note 3 : used codes are :  +00 to +99,  0+0 to 9+9, 00+ to 99+

note 4 :