Data from: 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 towards residence. However, these cross-cohort means obscured
substantial among-cohort variation in initial partial migration, and in
the subsequent effects of both plasticity and selective disappearance.
Here, plasticity reinforced versus counteracted selection at different
times, thereby reshaping the pattern of among-cohort variation in partial
migration across ages. These results show that early-life plasticity and
selection are both highly changeable, causing dynamic cross-age cohort
effects in a key life-history trait, yet preventing cross-cohort
age-specific phenotypic change.