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Résumé :
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Despite millions of ringed and recaptured birds, local as well as transient ones, questions about their migratory strategy are still under discussion. Numerous studies of captured individuals do not adequately reflect their behaviors. One of the least understood periods of migration is the period of preparation for the first migratory flight. Here, we show that adult Eurasian Reed Warblers (Acrocephalus scirpaceus) can accumulate considerable fat loads while still on their breeding sites. Seventeen local Reed Warblers were radio-tagged at the latest stages of breeding and tracked until their migratory departure. Eight of them were recaptured at least once prior to their nocturnal take-off from the breeding grounds. Recaptures during the pre-migratory period, including one on the actual day of departure, revealed significant fuelling (up to a fat score of 7 on a 9-point system) and a fuel load up to 40 % more than lean body mass. These reserves could allow them to fly several nights without refuelling.
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