van der Winden J. (2002) The odyssey of the Black Tern Chlidonias niger: Migration ecology in Europe and Africa. ARDEA 90 (3): 421-435

After breeding, Asian and European Black Terns Chlidonias niger concentrate in two European wetlands, IJsselmeer (The Netherlands) and Sivash (Ukraine), prior to their non-stop migration to wintering areas in coastal West Africa. Studies on their plumage, moult, body mass and feeding ecology in the post-breeding staging sites and in three African wintering areas (Ghana, Benin and Namibia) are reviewed in this paper. Throughout the year, Black Terns moult body feathers and primary moult is suspended only during the breeding period. Up to three waves of primary moult may occur simultaneously. The wing gap due to missing and growing primaries is largest just before migration in spring and late summer. At the IJsselmeer, body mass increased with 25-30% within a period of two to three weeks and such departure masses enable long non-stop flights of more than 3600 km. Black Terns ascend in the evening to high altitudes (>500 m) and start migration at night, a behaviour similar to long-distance migrating waders. Indeed, no important Black Tern stopover sites are known between IJsselmeer/Sivash and West Africa. In Namibia a similar mass increase was noticed prior to northward spring migration. In both areas Black Terns were able to moult primaries and store fat simultaneously. During the non-breeding season Black Terns depend mainly on relative large prey, especially shrimps and fish. Shrimps were the dominant prey type in Namibia and Benin. Food availability seemingly explained their migration patterns to a major extent. IJsselmeer and Sivash appear rich enough for Black terns to combine a rapid moult with fat storage. In West Africa, Black Terns concentrate at rich coastal ecosystems characterised by deep-water upwellings and high primary production. In Aug-Oct, upwellings occur locally along much of the West-African coast line and in Feb-Mar warm water eddies in Namibia increase the availability of shrimps. In March, high shrimp abundance in coastal lagoons in Benin again provides Black Terns with excellent feeding conditions. In Dec-Feb large concentrations of Black Terns have not been reported, but this study suggests these to be present at the productive offshore upwelling in the Gulf of Guinea or off the Angolan coast