Revealing different migration strategies in a Baltic Common Tern (Sterna hirundo) population with light-level geolocators

The Common Tern (Sterna hirundo) is one of Germany's farthest migrating bird species. Ringing studies have shown the use of the East Atlantic flyway, and according to their main wintering areas at the western and southern African coasts, German and European Common Tern populations have been divided into two allohiemic groups. However, first ring recoveries of German Common Terns in Israel indicated that some of the birds breeding in eastern Germany cross central Europe and migrate along the eastern African coast. To investigate the migratory behavior of Common Terns from East Germany, we fitted 40 Common Terns breeding in a colony at the German Baltic coast with light-level geolocators. Twenty-four loggers with analyzable datasets could be retrieved, revealing two different migratory strategies within one population. Seventeen individuals (70.83%) used the eastern Atlantic flyway and spent the winter at the western African coast, the Gulf of Guinea and the southern African coast, while the other individuals (n = 7; 29.17%) crossed central Europe, migrated along the eastern African coast and overwintered in the Mozambique Channel and South African coast. We, therefore, suggest to add a third allohiemic group to complement the picture of European Common Tern migration. Moreover, our results provide new knowledge and open new questions, which can be used for future studies regarding the evolution of different migratory strategies and its consequences in relation to climate change.

Automated summary

The Common Tern population in Germany exhibits two distinct migratory strategies, with some birds wintering on the western African coast and others migrating along the eastern African coast. This study reveals new knowledge about the migratory behavior of Common Terns from East Germany and raises questions about the evolution and consequences of different migratory strategies in relation to climate change.