Location data
Positions were obtained from light-level data using a threshold method (supporting information) following established procedures (Lisovski et al. 2019). Areas of apparent residency were identified over the non-breeding season (August to March) using Lavielle segmentation, following methods from Amelineau et al. (2021), and mean distance to the colony of each area of residency was calculated. Migratory effort was described as the distance to the furthest point of residency from the colony.