In the context of rapid climate change, phenological advance is a key adaptation for which evidence is accumulating across taxa. Among vertebrates, phenotypic plasticity is known to underlie most of this phenological change, while evidence for micro-evolution is very limited and challenging to obtain. In this study, we quantified phenotypic and genetic trends in timing of spring migration using 8032 dates of arrival at the breeding grounds obtained from observations on 1715 individual common terns (Sterna hirundo) monitored across 27 years, and tested whether these trends were consistent with predictions of a micro-evolutionary response to selection. We observed a strong phenotypic advance of 9.3 days in arrival date, of which c. 5% was accounted for by an advance in breeding values. The Breeder’s equation and Robertson’s Secondary Theorem of Selection predicted qualitatively similar evolutionary responses to selection, and these theoretical predictions were largely consistent with our estimated genetic pattern. Overall, our study provides rare evidence for micro-evolution underlying (part of) an adaptive response to climate change in the wild and illustrates how a combination of adaptive micro-evolution and phenotypic plasticity facilitated a shift towards earlier spring migration in this free-living population of common terns.

Data used for models presented in: Micro-evolutionary response of spring migration timing in a wild seabird by Moiron M, Teplitsky C, Haest B, Charmantier A†, Bouwhuis S† († = shared last authors) published in Evolution Letters. for information regarding the analyses, please contact mariamoironc@gmail.com for information regarding the data, please contact sandra.bouwhuis@ifv-vogelwarte.de if you'd like to use the data, please also contact sandra.bouwhuis@ifv-vogelwarte.de These data are part of those collected in an ongoing individual-based longitudinal population study additional data are likely to be available, and we are often very happy to collaborate provided that none of our own staff or students is working on a conflicting project.