1. aDepartment of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
2. bMax-Planck-Institute for Ornithology, Eberhard-Gwinner-Str., DE-82319 Seewiesen, Germany
3. cMax-Planck Comparative Cognition Research Station, ES-Loro Parque Fundación, 38400 Puerto de la Cruz, Tenerife, Spain