Carry-over effects of seasonal migration on reproductive success through breeding site retention in a partially migratory bird

Understanding the maintenance and dynamics of phenotypic polymorphisms requires unpicking key ecological mechanisms shaping the fitness costs and benefits of expressing alternative phenotypes, generating selection. Seasonal migration versus year-round residence expressed in partially migratory populations represents one common polymorphism that can experience strong selection through differential reproductive success. Yet, key hypothesised pathways that could generate such selection remain to be empirically tested.
One hypothesis is that migratory tactics affect subsequent reproductive success through carry-over effects on breeding site retention and resulting breeding dispersal. By remaining in breeding areas all year round, residents could retain their preferred breeding site between years, and consequently have higher reproductive success. Conversely, migrants that escape harsh non-breeding season conditions could return in better condition, with high resource holding potential, and ..., This data consists in observational data that have been collected in the field based on bird rings. Migratory tactic estimation are based on a modelling approach, as detailed in the article. , , # Data from: Carry-over effects of seasonal migration on reproductive success through breeding site retention in a partially migratory bird

[https://doi.org/10.5061/dryad.ffbg79d2t](https://doi.org/10.5061/dryad.ffbg79d2t)

These datasets were used to study the link between migratory tactic, dispersal behaviour and reproductive success in a partially migratory seabird, the European shag. This work is published in the Journal of Animal Ecology. Thanks to observations of ringed shags along the coast of Scotland year-round, we had access to nesting and non-breeding location of many ringed birds.

## Description of the data and file structure

The data consists in two files: \"migratory_tactic_2017-2021.csv\" and \"dispersal_2018-2021.csv\". We describe below the meaning of each column. All missing data are coded as *NA*.

### migratory\_tactic\_2017-2021.csv

This file is set up at the non-breeding season level, providing migratory tactic estimation, individual age, and for most, reproductive...