Spring nocturnal migration of Reed Warblers Acrocephalus scirpaceus: departure, landing and body condition

Abstract

Nocturnal migration of Reed Warblers Acrocephalus scirpaceus was studied by trapping with ‘high nets’ on the Courish Spit (Eastern Baltic) during spring 1998–2000. In spring, Reed Warblers left the stopover site between 45 and 240 min after sunset (median 84 min), although 85% of birds took off between 45 and 120 min after sunset. Birds did not arrive until the fifth hour after sunset; 67% of birds ended their nocturnal flights in the penultimate hour before sunrise, i.e. at dawn. At the moment of migratory departure, the average Reed Warbler body mass was 12.79 ± 0.66 g (n = 60). Average body mass of birds ending migratory flight was 11.69 ± 0.67 g (n = 18). The difference was highly significant. However, more than half of the birds completed migratory flights with a considerable fuel load, and some even had energy stores sufficient for a migratory flight on the next night. The spring migratory strategy of Reed Warblers over Central and Northern Europe probably includes a succession of short migratory flights (4–6 h) during several subsequent nights with 1‐day stopovers.