The recent climate change has an influence on the migration phenology of birds. With increasingly warmer winters, an increasing number of species are shortening their migration distance, and especially interesting are the cases of Trans-Sahara migrants, such as the Eurasian Reed Warbler (Acrocephalus scirpaceus), that choose the Iberian Peninsula as a new wintering area. This species is normally present in Spain from February (when it arrives to breed) to November (when autumn migration comes to an end), but the number of wintering records has increased in the last few decades. The aims of the present study are: to compile wintering records of the species in the Iberian Peninsula, to characterize those areas where the environmental conditions are favourable for the species in this period, when the species is supposed to be in Africa (south of Sahara desert) and to study the origin of wintering birds and their preferred wintering areas. Biogeographical favourability models were built and results show that the most favourable areas are coastal zones with mild temperatures, as it seems that minimum temperature is the environmental limitation for the presence of the species. The detailed analysis of the Eurasian Reed Warbler adjustments on migration, in the context of the current climate change, may facilitate to delve into the mechanisms affecting this phenomenon, and the extrapolation of the proposed methodology to other Trans-Sahara migrants with similar phenology shifts.
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