Populationsutveckling hos kentsk tärna Thalasseus sandvicensis i Sverige 2007–2023

The breeding grounds of the North Atlantic population of Sandwich Tern Thalasseus sandvicensis range along the coasts of western Europe and in the Baltic Sea: predominantly in the Netherlands, UK, France, Germany, and Denmark, with a smaller fraction of the population breeding in southern Sweden. This population has fluctuated strongly in size in recent decades due to human activities, pollution, changing availability of food, and outbreaks of highly pathogenic avian influenza. To evaluate whether management actions to further protect the species are needed in Sweden, better knowledge about the recent development of the breeding population is required. We found that the total number of breeding pairs in Sweden between 2007 and 2014 fluctuated between c. 390 and c. 570 pairs. Later, the number increased markedly from c. 630 pairs in 2015 to c. 1,830 pairs in 2021. In 2022 and 2023, the number decreased partly due to avian influenza outbreaks and c. 1,540 pairs bred in 2023. Most pairs bred in the provinces of Blekinge, Gotland, and Skåne. The four largest colonies hosted c. 55% of the cumulative number of breeding pairs between 2007 and 2023. This aggregated distribution makes the species vulnerable to various threats.