The gull-billed tern (Gelochelidon nilotica) is a medium-sized tern whose last colony in Central Europe is located in the Elbe estuary of Dithmarschen (state of Schleswig-Holstein). By 2010, this population had shrunk to 41 breeding pairs, which led the state of Schleswig-Holstein to take responsibility for its preservation by founding a "Species conservation project for the gull-billed tern" in 2011, administrated by the ‘Bündnis Naturschutz in Dithmarschen e.V.’. The aim of the project is to prevent the extinction of the population and to ensure the protection of the large multi-species colony consisting of three species of terns, black-headed gulls, avocets, oystercatchers and other ground-nesting birds. Fencing to minimise mammalian predation pressure and habitat management currently are the main methods employed.

In 2021, we teamed up with the members of the conservation project to investigate the extent to which potential threats other than predation or habitat structure, such as food shortage (Schnelle et al. 2024a), limited genetic diversity (Schnelle et al. 2024b) or pollution could limit the growth of the population. After the outbreak of avian influenza in the breeding seasons of 2022 and 2023, we additionally started monitoring the development of antibodies against this viral disease in both the gull-billed terns and one of their host species, the common tern. Future work would benefit from extending our information about these birds beyond the breeding season or establishing further suitable breeding habitat to mitigate the risk associated with the population being in a single location.