ACKNOWLEDGEMENTS

We thank Gary Nunn, Jeremy J. Austin, Chris Gaskin, Juan E. Martínez-Gómez, and Maite Louzao for collecting tissue and blood samples from the field and/or providing tissue samples from museum skins for this study. We would also like to thank the many institutions that provided tissue loans for this research: Smithsonian National Museum of Natural History, Louisiana State University Museum of Natural Science, University of Washington Burke Museum, American Museum of Natural History, the University of Kansas Biodiversity Institute, and the Muséum National d’Histoire Naturelle. We thank the pertinent authorities for issuing the permits needed for this work. Finally, we would like to thank Josephine R. Paris for her comments on an early version of this manuscript and Martí Franch for his wonderful shearwater illustrations. Research funding was provided by the Fundación BBVA (program “Ayudas a Equipos de Investigación Científica 2017”, project code 062_17 to M.R.).