Data from: Temporal dynamics of selection on early-life phenotypic plasticity in seasonal migration versus residence

In this study, we quantified selection on early-life plasticity in the
ecologically critical trait of seasonal migration versus
residence, by fitting a novel multi-state model to spatio-seasonal
resighting data from 13 newly-fledged cohorts of partially migratory
European shags (Gulosus aristotelis). To obtain the required data, during
the 2010-2022 breeding seasons (April-August; 13 cohorts), all breeding
attempts on IoM were monitored, and >95% of fledglings were marked
with uniquely coded metal and colour rings. During the 2010-2024
non-breeding seasons, we undertook regular (approximately biweekly)
resighting surveys on IoM (and adjacent day roosts) to detect current
residents, and at core roost sites spanning the north-east UK coast
(predominantly ca. 100-500 km from IoM) to detect current migrants. We
formulated individual encounter histories as occasion-specific summaries
of resightings of 10,788 colour-ringed shags fledged during 2010-2022. We
defined five primary temporal ‘occasions’ spanning the natal breeding
season (June-July, when chicks are typically ringed before fledging) to
the following March (~8 months post-fledging, Figure 2), and an 'ever
after' occasion. The model outputs, i.e. posterior samples of the
model parameters and derived parameters, are the primary results of our
analyses.