SEEN - SE European Bird Migration Network
Time-dependent bimodal programme in the orientation behaviour of the European Paddyfield Warblers (Acrocephalus agricola) along E-W axis

Mihaela Ilieva & Pavel Zehtindjiev

Institute of Zoology, Bulgarian Academy of Sciences, Sofia, Bulgaria

By means of orientation experiments the endogenous directionality of local Paddyfield Warblers breeding in Durankulak Lake was studied in the autumn of 2005. The species breeds only in the northernmost part of the Bulgarian Black Sea coast and winters in the region of Indian peninsula. The question is if they migrate along the historical expansion pathway (NNE) circumventing Black Sea in autumn or choose the direct route across the sea (ESE). Birds were mistnetted in early autumn and tested in the field experiments. The same birds were kept in aviaries during the rest of the autumn season and tested regularly in Emlen funnels. It was found out that the Black Sea has prevented this species to adapt a more direct flight route, which means that the Black Sea is (at least for this species) an efficient barrier. The species demonstrated in the set of experiments change in the migratory direction from NE to SE during the ongoing course of autumn migration. It means that the westernmost population of the Paddyfield Warbler in Europe still follows the historical breeding range expansion and selection has not forced them to take the direct route. The Bulgarian population starts autumn migration in NNE direction – along the Black Sea coast tracing possible former time expansion of the species (registered for the first time in Bulgaria in 1968) and following shift to SE migratory direction towards present wintering sites is confirmed by our experiments. Time-dependent bimodal programme (Zugknick) in the orientation behaviour of a migratory species along E–W axis has been demonstrated for the first time.

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