1. Department of Environmental Sciences, Faculty of Natural Sciences , Constantine the Philosopher University in Nitra , Tr. A. Hlinku 1, SK- 949 01 Nitra , Slovakia .
2. Raptor Protection of Slovakia , Trhová 54, SK- 841 01 , Bratislava , Slovakia .
3. Swiss Ornithological Institute , Seerose 1, CH- 6204 Sempach , Switerzland .