Early-life variation in migration is subject to strong fluctuating survival selection in a partially migratory bird

Population dynamic and eco-evolutionary responses to environmental variation and change fundamentally depend on combinations of within- and among-cohort variation in phenotypic expression of key life-history traits, and on corresponding variation in selection on those traits. Specifically, in partially migratory populations, spatio-seasonal dynamics depend on the degree of adaptive phenotypic expression of seasonal migration versus residence, where more individuals migrate when selection favours migration.
Opportunity for adaptive (or, conversely, maladaptive) expression could be particularly substantial in early life, through initial development of migration versus residence. However, within- and among-cohort dynamics of early-life migration, and of associated survival selection, have not been quantified in any system, preventing any inference on adaptive early-life expression. Such analyses have been precluded because data on seasonal movements and survival of sufficient young individ..., The data come from a long-term study of European shags (Gulosus aristotelis) breeding the Isle of May National Nature Reserve, Scotland (56°11'5.40\"N, 2°33'16.19\"W). The data  comprise capture-recapture history data derived from field-ring-resighting data from 11 cohorts of first-year juveniles between 2010 and 2020. Codes for bespoke multi-state capture-mark-recapture models are provided. , , # Data from: Within- and among-cohort variation in early-life migration is subject to strong fluctuating survival selection in a partially migratory bird

[https://doi.org/10.5061/dryad.r4xgxd2mf](https://doi.org/10.5061/dryad.r4xgxd2mf)

The data comprises summaries of field observations required to reproduce the analyses presented in the manuscript: Within- and among-cohort variation in early-life migration is subject to strong fluctuating survival selection in a partially migratory bird. Associated R and STAN code are also provided.

Authors: Cassandra R. Ugland, Paul Acker, Sarah J. Burthe, Rita Fortuna, Carrie Gunn, Thomas R. Haaland, Michael P. Harris, Timothy I. Morley, Mark A. Newell, Robert L. Swann, Sarah Wanless, Francis Daunt, and Jane M. Reid
January 2024

Study population: A population of European shags (*Gulosus aristotelis*) breeding on Isle of May National Nature Reserve (hereafter ‘IoM’), Scotland (56°11'5.40\"N, 2°33'16.19\"W).

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