Dark blue ring with a white 2 alpha-numeric code (on tarsus) and metal ring on the opposite tarsus.
note 1 : a joint project of the Research Institute for Nature and Forest/INBO, Bureau Waardenburg and Ringgroup Delta on breeding and feeding ecology. This project will run for the next five years. Some 30 birds ringed in 2010.
note 2 : the colour-ring is added to aid identification of birds (formerly) carrying transmitters in the breeding colonies in the southwest of The Netherlands. Reports from further afield are more than welcome !