Funding for this research was provided by:
niedersächsisches ministerium für wissenschaft und kultur (74ZN1477)
Institut für Vogelforschung - Vogelwarte Helgoland
Received: 7 July 2021
Accepted: 13 October 2021
First Online: 21 October 2021
: Trapping, ringing and handling of the birds comply with the law of the Federal State of Schleswig–Holstein, Germany.
: Not applicable.
: The authors declare that they have no competing interests.