1. Max Planck Institute for Ornithology, Vogelwarte Radolfzell, Schlossallee 2, 78315 Radolfzell, Germany
2. Departamento de Ecologia, ICB, Universidade Federal de Goiás, CP. 131, 74001-970 Goiânia, Brazil
3. Imperial College London, Silwood Park, Ascot, Berkshire SL5 7PY, UK