Wetlands are highly productive habitats that are largely used by many avian species as stopover sites during their migrations. However, these habitats are highly threatened by anthropogenic activities, such as land use changes, the introduction of exotic species and global warming. Further understanding on the spatiotemporal use of wetlands and their surrounding areas by migrating birds is essential to predict how these changes might affect avian en route ecology. We selected a habitat-generalist passerine of conservation concern, the Bluethroat Luscinia svecica, as model of how migratory birds exploit a highly anthropogenic river basin in southwestern France (i.e. Barthes de la Nive) during autumn migration. We captured and radiotracked 29 young Bluethroats in this region to shed light on different aspects of their stopover ecology and behaviour, such as stopover duration, habitat selection and home range size. We also complemented the study with a characterization of Bluethroat diet and arthropod availability in different habitats. Bluethroats positively selected reedbeds (pure or mixed associated with carex), hydrophilous tall grasslands and corn crops. Birds staying more than just one day, 8.4 days on average, used preferably corn crops. Home range sizes were on average 5.8 ha (fixed kernels K95) and high occupancy area (K50) was 1.36 ha with large individual variation. Bluethroats stopping over with low body reserves tended to have larger home ranges and used preferentially corn crops, wet or mesotrophic grasslands and rural paths. Reedbeds were typically used as roosting habitat for the majority of birds, being on average 397 m apart from their daytime core areas. Short-staying birds tended to show higher body reserves and restricted their activities to a smaller home range (1 ha) in pure and mixed reedbed. The diet of Bluethroats was dominated by ants Hymenoptera Formicidae, Araneidae and Coleoptera that were most abundant in the corn crops. The use of corn crops by migrating Bluethroats during autumn in our study site appears to be a reasonable solution in a highly altered environment. Reducing the use of insecticides in these crops and delaying the harvesting time after mid-October are two measures that could favour Bluethroats and other migratory species while natural wetlands are restored and reedbeds protected from tree encroachment. ACKNOWLEDGEMENTS -This work was supported by the Conseil Départemental des Pyrénées Atlantiques, Syndicat Nive Maritime, Villefranque and Bayonne councils. We are particularly grateful to F. Esnault, S. Valles, R. Damestoy and R. Dufourcq. We are extremely thankful to L. Delalande, F. Delfour, A. Glad, M. Janczyszyn-Le Goff, T. Sarraude, for their commitment in the collection of the radiotracking data, to L. Julien for invertebrate sampling, and members of OISO association who made this research possible, especially F. Lartigau. National Museum of Natural History authorized the bird-ringing and radio-tracking scheme. The experiments were complied with the current laws of ...
