1. Population Biology/EBCNorbyvägen 18DSE‐752 36UppsalaSweden
2. Department of Zoology, Chinese Academy of SciencesBeijing100080PR China
3. Max Planck Research Centre for Ornithology, Vogelwarte Radolfzell, Schloss MöggingenSchlossallee 2D‐78315RadolfzellGermany