About the Authors
Department of Cognitive Biology, University of Vienna, Vienna, Austria
Max-Planck-Institute for Ornithology, Seewiesen, Germany
Department of Zoology, University of Oxford, Oxford, United Kingdom
The authors have declared that no competing interests exist.
Conceived and designed the experiments: AA, AB. Performed the experiments: AA, Constanze Riha (see acknowledgements). Analyzed the data: AA. Contributed reagents/materials/analysis tools: AA AB AK. Wrote the manuscript: AA AK AB.