Upwelling systems in the migration ecology of Roseate Terns (Sterna dougallii) breeding in northwest Europe

Abstract

For migratory seabirds, staging and wintering areas may be important targets for conservation. Declines of Roseate Tern Sterna dougallii populations have led to conservation initiatives at breeding sites on both sides of the North Atlantic. However, these could be compromised by environmental conditions in non-breeding areas. The migratory ecology of Roseate Terns is poorly known and we used light-level biologgers (geolocators) to identify the migratory routes, staging and wintering areas of Roseate Terns from two European colonies. Most birds wintered off the Ghanaian coast in the Gulf of Guinea, but some wintered further west off Sierra Leone and Liberia, or changed locations during the winter. In these areas, cold-water upwellings of the Guinea Current Large Marine Ecosystem (GCLME) may provide vital foraging resources. Geolocations in combination with temperature measurements and satellite sea-surface temperature data show that cold-water upwellings of the Canary Current Large Marine Ecosystem (CCLME) were important areas for migratory staging, particularly on the return migration which was slower than the outward journey. These results emphasize the importance of productive cold-water upwellings in the migratory ecology of Roseate Terns. The GCLME and CCLME are under threat from over-exploitation, pollution and climate change; effective conservation of these environments will be important to secure the long-term future of these and other seabirds.