1. a School of Biology , University of St Andrews , Bute Building, St Andrews, Fife , KY16 9TS , UK
2. b AP Leventis Ornithological Research Institute , University of Jos Biological Conservatory , PO Box 13404, Laminga, Jos , Plateau State , Nigeria
3. c Hawk Conservancy Trust , Weyhill, Andover , SP11 8DY , UK
4. d Ottenby Bird Observatory , Pl 1500, SE-380 65 , Degerhamn , Sweden
5. e Scottish Natural Heritage , Inverdee House, Baxter Street, Aberdeen , AB11 9QA , UK
6. f BioConsult SH , Brinckmannstrasse 31, 25813 , Husum , Germany