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Résumé :
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Nocturnal passerine migrants ringed at daytime stopovers can be retrapped at the moment of initiating nocturnal flight by the original method of high mist-nets. This technique was developed and applied at the field site 'Rybachy' where thousands of birds, primarily nocturnal passerine migrants, are annually trapped in a joint research project of the Biological Station and the Vogelwarte Radolfzell. Two lines of high mist-nets (overall length 220 m) are placed on wooden pathways over the tops of bushes and reed ca. 7 m above the ground. Nets are opened daily 2 h before sunset and checked every hour until sunrise. At spring migration in 1998-99 a total of 67 previously ringed individuals of 16 species were trapped by this method. At autumn migration in 1997-98 107 birds of 23 species were trapped. Largest data sets are available for Robins (Erithacus rubecula, 49 birds in autumn and 13 in spring) and for Reed Warblers (Arcocephalus scirpaceus, 10 and 21 individuals respectively). This method allows to determine (1) stopover length, (2) departure time, and (3) body condition (body mass, fat stores). In each species a very broad variation in departure time and in body condition were recorded. For marked local birds information on date, period of night, body mass, fat stores and moult status at departure for their first migratory flight are obtained.
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