Early-life stasis in partial seasonal migration is underpinned by among-cohort variation in migratory plasticity and selective disappearance

Life-history traits expressed through early life may exhibit considerable among-cohort variation, affecting population age-structure and resulting dynamics. Yet, initial among-cohort variation could be substantially reshaped by dynamic combinations of labile plasticity and selective disappearance acting within and among cohorts across years and ages. However, such dynamics are rarely quantified for any trait, impeding the prediction of phenotypic outcomes. We quantified overall early-life phenotypic stasis versus change, and underlying dynamics of plasticity and selection, for the key life-history trait of seasonal migration versus residence by fitting multi-state models to multi-year ring-resighting data from 11 cohorts of partially migratory European shags (Gulosus aristotelis). Although the cross-cohort proportion of migrants remained approximately constant across the four years following fledging, there was a selective disappearance of sub-adult residents balanced by net plasticity ..., 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 sub-adult individuals fledged on the Isle of May between 2010 and 2020. Codes for bespoke multi-state capture-mark-recapture models are provided. , # Data from: Early-life stasis in partial seasonal migration is underpinned by among-cohort variation in migratory plasticity and selective disappearance

The data comprises summaries of field observation data required to reproduce the analyses presented in the manuscript: 
Early-life stasis in partial seasonal migration is underpinned by among-cohort variation in migratory plasticity and selective disappearance.

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

## Files are summarised below

R scripts are annotated to explain steps and definitions of all variables
Code was written and used with R version 4.3.2 and STAN v2.32.5

## Description of the data and file structure

Here we include two R scripts and one STAN model script, 1 excel file with the capture-mark-recapture histories for all 11 cohorts (2010...2020), in addition to several excel files with the estima...,