Acknowledgements
We are grateful to Frédéric Angelier, Muhammad Asghar, Els Atema, Michaël Beaulieu, Staffan Bensch, Pierre Bize, Piérre Blevin, Olivier Chastel, François Criscuolo, Adriana Dorado-Correa, Mathieu Giraudeau, Dennis Hasselquist, Britt Heidinger, Lisa Jacquin, Alexander Kitaysky, Sophie Lardy, Jimena López-Arrabé, Pat Monaghan, Jose Noguera, Joacim Näslund, Mats Olsson, Marco Parolini, Lorenzo Pérez-Rodrígues, Sophie Reichert, Nicky Rollings, Pablo Salmón, Manrico Sebastiano, Joanna Sudyka, Mathilde Tissier, Oscar Vedder, Simon Verhulst, Hannah Watson, Tony Williams, and Rebecca Young for sharing raw data of their published work. We especially thank Mark Haussmann and Barbara Tschirren for sharing their unpublished data on the Japanese quail. This study was financially supported by the Finnish Cultural Foundation Varsinais-Suomi Regional Fund (TK), Turku University Foundation, Finnish Cultural Foundation (TK), the Ella & Georg Ehrnrooth Foundation (MB) and the Turku Collegium for Science and Medicine (AS).