1. Ornithological Station, Faculty of Biological Sciences, University of Wrocław, Wrocław, Poland
2. Lower SIlesian Division, Silesian Ornithological Society, Wrocław, Poland
3. Division of Nature Protection, Chełmy Countryside Park, Myślibórz, Poland
4. Natural History Museum, Faculty of Biological Sciences, University of Wrocław, Wrocław, Poland
5. Ecology of Animal Societes, Max Planck Institute of Animal Behavior, Radolfzell, Germany
6. Department of Behavioural Ecology, Faculty of Biological Sciences, University of Wrocław, Wrocław, Poland