Geography and Site‐Specific Factors, Rather Than Recent Climate, Dominated Spanish Wintering Bird Communities

Aim To assess the extent to which climatic, environmental, geographic and sampling‐related variables shaped species composition and the components of β‐diversity (turnover and nestedness) in wintering bird communities during the last 25 years across the eastern Iberian Peninsula. Location Eastern Iberian Peninsula, across 78 sites in Spain. Taxon Ninety seven thousand one hundred and ninety‐seven birds ringed and recorded from December to February between 1997 and 2022. Methods We used Mixed Graphical Models (Graphical Lasso) to study the covariation between environmental and geographic variables and taxonomy‐based components of β‐diversity (turnover and nestedness), accounting for differences in the sampling efforts. Additionally, we analysed the associations between individual species abundances, overall species richness and the environmental variables. The resulting species groupings were further tested for trait‐based patterns. Finally, we assessed spatiotemporal trends in bird abundance, presence–absence data and climatic variables to evaluate potential long‐term changes. Results Our results indicate that spatial turnover was the dominant process shaping β‐diversity across study sites. The Mixed Graphical Models revealed that dissimilarity in elevation, habitat and sampling effort primarily drove turnover and nestedness, and that the assemblages remained largely stable during the 25‐year study period. Overall, species presence was associated with site‐specific factors, while species richness was incidentally correlated positively with eight forest bird species. Only six species exhibited significant trends driven solely by temporal effects, whereas most species were driven by longitude alone or combined spatiotemporal factors, suggesting strong site‐specific responses and no consistent general pattern in the region. Although not statistically significant, maximum temperature variables exhibited a positive temporal trend, suggesting gradual warming on the condition preceding each survey during the study period. Main Conclusions The stability in wintering bird assemblages in the Iberian Peninsula may be attributed to its geographical position in temperate zones, which could reduce the sensitivity of bird assemblages to climatic variability at intermediate latitudes. This contrasts with patterns reported at northern and tropical latitudes. In addition, this relative resilience might also reflect the dominance of widespread generalist species, which tend to tolerate environmental fluctuations and can mask early signals of climate‐induced community change. These results underscore the need for conservation strategies tailored to spatial variability and local site‐specific conditions, with particular emphasis on maintaining habitat diversity and safeguarding areas that encompass representative elevational and climatic gradients.