[1] Univ Copenhagen, Ctr Macroecol Evolut & Climate, Dept Biol, DK-1168 Copenhagen, Denmark
[2] Univ Turku, Sect Ecol, SF-20500 Turku, Finland
[3] Inst Avian Res, Vogelwarte Helgoland, Germany
[4] Univ Copenhagen, Zool Museum, DK-1168 Copenhagen, Denmark