Body mass and fat reserves of Sedge Warblers during vernal nocturnal migration: departure versus arrival

Abstract

Body mass and fat reserves of Sedge Warblers (Acrocephalus schoenobaenus) on nocturnal departure and arrival were studied by two methods (capture in high nets and playback of songs) on the Courish Spit (Eastern Baltic, Russia) in spring 1998–2000. The average body mass of departing Sedge Warblers was 13.7 g, and the average body mass of arriving birds was 13.1 g. The difference between arrival and departure masses was not significant. The calculated flight range of departing Sedge Warblers in still air varied from 19 to 665 km, with a mean of 295 km. The high fuel loads of Sedge Warblers on departure and on arrival may be explained by the necessity for Scandinavian populations to cross the Baltic; the risk of drifting out to sea for birds migrating over land; or the general vernal migratory strategy of Sedge Warblers, involving a series of short (4.5–6.2 h) flights on several consecutive nights.