We ring the chicks with metal rings from the bird observatory Helgoland (with the permission of the authorities). This does not bother the birds, and some feel that they are even "proud" of their ring. The ring number allows us to differentiate them individually and to estimate how many chicks will fledge each year.
So we get some information about the flyway of "our" birds (Channel and East Atlantic Coast) and the winter area at the coast off West Africa. There, the terns spend their first summer before they fly back to the breeding areas. For the first time they fly in the age of two or even three years back. They start with their first brood at the age of three or four.