Project title
We acknowledge funding from University Paris-Sud. H. Robles was funded by FUNDAME and Xunta de Galicia (“ Angeles Alvari~no” and “Plan I2C” postdoctoral programs). M. Eens and R. Pinxten acknowledge funding of FWO-Flanders and the University of Antwerp. E. Barba acknowledges funding of project CGL2013- 48001-C2-1-P (Spanish Ministry of Science and Innovation). The Montpellier blue tit team acknowledges funding from the OSUOREME, the French ANR, and the ERC (ERC- 2013-StG-337365-SHE to A. Charmantier).