Continent-wide drivers of spatial synchrony in breeding demographic structure across wild great tit populations

Variation in age structure influences population dynamics, yet we have limited understanding of the spatial scale at which its fluctuations are synchronised between populations. Using 32 great tit populations, spanning 4○W–33○E and 35–65○N involving >130,000 birds across 67 years, we quantify spatial synchrony in breeding demographic structure (subadult vs. adult breeders) and its drivers. We show that larger clutch sizes, colder winters, and larger beech crops lead to younger populations. We report distance-dependent synchrony of demographic structure, maintained at approximately 650km. Despite covariation with demographic structure, we do not find evidence for environmental variables influencing the scale of synchrony, except for beech masting. We suggest that local ecological and density-dependent dynamics impact how environmental variation interacts with demographic structure, influencing estimates of the environment’s effect on synchrony. Our analyses demonstrate the operation o..., Study systems and data collection
The great tit Parus major is a passerine bird found in mixed woodlands across much of the Western Palearctic. Their reproductive lifespan ranges from 1–9, averaging 1.8 years (Bouwhuis et al. 2009; Woodman et al. 2022). Although there are some continuous changes with age (Bouwhuis et al. 2009), the main age effects on individual-level traits and population processes are captured by two age-classes: 1-year-olds (hereafter subadults) and older (hereafter adults, Gosler 1993; Harvey et al. 1979; Perrins 1979; Gamelon et al. 2016, 2019; Woodman et al. 2022). Great tits generally undertake one breeding attempt during a single annual breeding season April–June (in some parts of their range second clutches can occur, Verhulst 1998; Visser et al. 2003). Data used here are from 32 populations, the geographical range of which represents a large part of the species’ breeding range (Sullivan et al. 2009). Generally, data collection at these sites included regular v..., , # Continent-wide drivers of spatial synchrony in breeding demographic structure across wild great tit populations

[Access this dataset on Dryad](https://doi.org/10.5061/dryad.k0p2ngfgg)

Presented here is the raw data (\"bred_dem_synchrony.RData\") and annotated R Script (\"Continent-wide drivers of spatial synchrony in breeding demographic structure across wild great tit populations.R\") needed to run analyses for the project \"Continent-wide drivers of spatial synchrony in breeding demographic structure across wild great tit populations\".

## Description of the data and file structure

\"bred_dem_synchrony.RData\": R-data file needed to run analyses. Descriptions of the three datasets within this file are found in the R script, and also below.

1. \"bred_dem_variables\" = Base data for annual breeding demographic structure variables of great tit populations. Only includes populations with annual population size equal or greater than 20 individuals and where 25% or more of individuals have be...