Terns

2 rings (without code) on right tarsus (usually on right, occasionally on left) and aluminium ring on left tarsus (usually on left, occasionally on right) (adults/juveniles).

note 1: before 1995 : only aluminum rings with code on left tarsus.

note 2: 1995 : light-green and white (both at the top as well as at the bottom) and green-yellow.

note 3: 1996 : no colourrings, only aluminium rings with code on left tarsus.

note 4 : 1997 : green at the top and yellow at the bottom (exceptional opposite).

note 5 : 1999 : some 600 juv. birds have been marked with a ring (green at the top and yellow at the bottom).

note 6: in 2000 only ad. birds have been marked with colourrings.