Among-individual and within-individual variation in seasonal migration covaries with subsequent reproductive success in a partially-migratory bird

Jane M. Reid* (Corresponding Author), Moray Souter, Sarah R. Fenn, Paul Acker, Ana Payo-Payo, Sarah J. Burthe, Sarah Wanless, Francis Daunt

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)
12 Downloads (Pure)


Within-individual and among-individual variation in expression of key environmentally sensitive traits, and associated variation in fitness components occurring within and between years, determine the extents of phenotypic plasticity and selection and shape population responses to changing environments. Reversible seasonal migration is one key trait that directly mediates spatial escape from seasonally deteriorating environments, causing spatio-seasonal population dynamics. Yet, within-individual and among-individual variation in seasonal migration versus residence, and dynamic associations with subsequent reproductive success, have not been fully quantified. We used novel capture-mark-recapture mixture models to assign individual European shags (Phalacrocorax aristotelis) to 'resident', 'early migrant', or 'late migrant' strategies in two consecutive years, using year-round local resightings. We demonstrate substantial among-individual variation in strategy within years, and directional within-individual change between years. Furthermore, subsequent reproductive success varied substantially among strategies, and relationships differed between years; residents and late migrants had highest success in the 2 years, respectively, matching the years in which these strategies were most frequently expressed. These results imply that migratory strategies can experience fluctuating reproductive selection, and that flexible expression of migration can be partially aligned with reproductive outcomes. Plastic seasonal migration could then potentially contribute to adaptive population responses to currently changing forms of environmental seasonality.

Original languageEnglish
Article number20200928
Number of pages9
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1931
Early online date22 Jul 2020
Publication statusPublished - 29 Jul 2020

Bibliographical note

We thank Raymond Duncan (Grampian Ringing Group), whose insatiable enthusiasm for ringing was inspirational. We thank everyone who contributed to fieldwork, especially Mike Harris and David Hunter; Roger Pradel for generous advice on CMR mixture models; and UK Natural Environment Research Council for funding (NE/R000859/1, NE/P009719/1).

Data accessibility
Data are available from the Dryad Digital Repository: [46].
Electronic supplementary material is available online at


  • Annual reproductive success
  • capture-mark-recapture mixture model
  • fluctuating selection
  • partial migration
  • phenotypic plasticity
  • spatial population dynamics
  • annual reproductive success


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