Authors: Kira E. Delmore, Benjamin M. Van Doren, Greg J. Conway, Teja Curk, Tania Garrido-Garduño, Ryan R. Germain, Timo Hasselmann, Dieter Hiemer, Henk P. van der Jeugd, Hannah Justen, Juan Sebastian Lugo Ramos, Ivan Maggini, Britta S. Meyer, Robbie J. Phillips, Magdalena Remisiewicz, Graham C. M. Roberts, Ben C. Sheldon, Wolfgang Vogl and Miriam Liedvogel
Publication: Proceedings of the Royal Society B
Publication Link: https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1339
Keywords: migration, divide, timing, songbird, speciation, assortative mating
Abstract: Seasonal migration is a complex and variable behaviour with the potential to promote reproductive isolation. In Eurasian blackcaps (Sylvia atricapilla), a migratory divide in central Europe separating populations with southwest (SW) and southeast (SE) autumn routes may facilitate isolation, and individuals using new wintering areas in Britain show divergence from Mediterranean winterers. We tracked 100 blackcaps in the wild to characterize these strategies. Blackcaps to the west and east of the divide used predominantly SW and SE directions, respectively, but close to the contact
zone many individuals took intermediate (S) routes. At 14.0° E, we documented a sharp transition from SW to SE migratory directions across only 27 (10–86) km, implying a strong selection gradient across the divide. Blackcaps wintering in Britain took northwesterly migration routes from continental European breeding grounds. They originated from a surprisingly extensive area, spanning 2000 km of the breeding range. British winterers bred in sympatry with SW-bound migrants but arrived 9.8 days earlier on the breeding grounds, suggesting some potential for assortative mating by timing. Overall, our data reveal complex variation in songbird migration and suggest that selection can maintain variation in migration direction across short distances while enabling the spread of a novel strategy across a wide range.