1. Department of Biology, University of Pisa, Via Volta 6, 56126 Pisa, Italy
2. Department of Oceanography and Fisheries, IMAR centre of the University of the Azores, 9901-862 Horta, Azores, Portugal
3. Max Planck Institute for Ornithology, Department of Migration and Immuno-ecology, Schlossallee 2, Radolfzell 78315, Germany
4. CNRS/CEFE, 1919, route de Mende, 34293 Montpellier Cedex 5, France