1. School of Biological Sciences, Monash University, Clayton, Victoria, Australia
2. Behavioural and Physiological Ecology, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, The Netherlands
3. Max Planck Institute for Ornithology, Vogelwarte Radolfzell, Radolfzell, Germany
4. School of BioSciences, University of Melbourne, Parkville, Victoria, Australia