Skip to main content

Differential changes in lifecycle-event phenology provide a window into regional population declines

Cite this dataset

Hanmer, Hugh; Boersch-Supan, Philipp; Robinson, Robert (2022). Differential changes in lifecycle-event phenology provide a window into regional population declines [Dataset]. Dryad.


Climate change affects the phenology of annual lifecycle events of organisms, such as reproduction and migration. Shifts in the timing of these events could have important population implications directly, or provide information about the mechanisms driving population trajectories, especially if they differ between lifecycle event. We examine if such shifts occur in a declining migratory passerine bird (Willow Warbler, Phylloscopus trochilus), which exhibits latitudinally diverging population trajectories. We find evidence of phenological shifts in breeding initiation, breeding progression and moult that differ across geographic and spring temperature gradients. Moult initiation following warmer springs advances faster in the south than in the north, resulting in proportionally shorter breeding seasons, reflecting higher nest failure rates in the south and in warmer years. Tracking shifts in multiple lifecycle events allowed us to identify points of failure in the breeding cycle in regions where the species has negative population trends, thereby demonstrating the utility of phenology analyses for illuminating mechanistic pathways underlying observed population trajectories.


We leverage observations of three lifecycle events (egg laying, brood patch re-feathering, moult) from two large-scale citizen science schemes, the UK Nest Record Scheme (Crick et al. 2003) and the British and Irish Ringing Scheme (Baillie et al. 1999), collected from 2000 – 2018 across Great Britain and operated by the British Trust for Ornithology (BTO) in partnership with the Joint Nature Conservation Committee (JNCC). Nest recording and ringing occur at volunteer selected sites, with brood patch and moult records generally originating at ringing sites. Both schemes achieve broad coverage across Great Britain, although records south of 51˚N and north of 57˚N were excluded for both schemes due to low sample sizes and inconsistent sampling in these areas.

Usage notes

All files are in text based formats.


British and Irish Ringing Scheme