Institute of Ornithology Croatian Academy of Sciences and Arts Gunduli?eva 24 10000 Zagreb Croatia;
Poultry Centre Croatian Veterinary Institute Hein-zelova 55 10000 Zagreb Croatia;
Balaton-felvidéki National Park Directorate Csopak 8229 Hungary;
Department of Limnology University of Pannonia Veszprém 8200 Hungary;
Balaton Limnological Institute MTA Centre for Eco-logical Research Tihany 8237 Hungary.;