1. aDepartment of Cognitive Science, Lund University, Sweden
2. bDepartment II of Biology, Ludwig-Maximilians-University Munich, Germany
3. cMax Planck Comparative Cognition Research Station, Loro Parque Fundacion, 38400 Puerto de la Cruz, Tenerife, Spain
4. dMax Planck Institute for Ornithology, Seewiesen, Germany