Acknowledgements
We are grateful to Dr C. Saraux and Dr B. Warren for helpful comments on the phylogenetic and statistical analyses. The authors wish to thank Dr A. Pauliny, Dr D. Lank, Dr M. Enstipp, Dr P. Bize and Dr D. Gremillet for providing us with personal information on their biological models. We are grateful to Sebastian Sosa for providing us with R script for the radial distribution of bird species in relation to Adult TL and PC axes. FSD thanks the Institute of Advanced Studies of the University of Strasbourg for their financial support through an USIAS fellowship, and the Région Grand Est and the Eurométropole de Strasbourg for the award of a Gutenberg Excellence Chair that supported this project.