Warm or Dry Springs (Still) Boost the Reproduction of Most Temperate Songbirds

ABSTRACT Aim Nonlinearities are ubiquitous features of ecosystem dynamics in climate change ecology. The changing climate is expected to reveal hump‐shaped patterns in ecosystem responses, delineating weather optima and constraints. In temperate mid‐latitudes, both cold and warm spring constraints are reported to limit songbird breeding productivity. However, with many studies focusing on specifically declining functional groups, such as long‐distance migrants, our understanding of the overall influence of increasingly warmer and drier conditions on songbird productivity remains limited. Here, we modelled changes in songbird productivity in relation to temperature and water balance anomalies during the breeding season, aiming to identify key weather constraints—whether life‐history dependent or shared across species—in a warming temperate world. Location France. Time Period 1991–2022. Major Taxa Studied Songbirds ( Passeri ). Methods Using standardised capture data of 300,031 birds across 68 species, we quantified changes in songbird productivity along gradients of spring weather anomalies and extremes using generalised linear mixed models. We then conducted interspecific analyses to explore how life‐history traits (e.g., migratory strategy, thermal and hydric affinities) modulate species' sensitivity to weather. Results Songbird productivity increased along gradients from cold to warm and from wet to dry anomalies. Nonetheless, warm‐related constraints also emerged: in early spring, particularly at already warm sites and most strongly for long‐distance migrants; and in late spring, especially for cold‐adapted species. Main Conclusions Warmer or drier springs continue to enhance songbird productivity in temperate France, reaffirming the detrimental influence of cold and wet snaps. Beyond the well‐known benefits of earlier breeding phenologies, these effects are likely driven by the impacts of such weather conditions on ecosystem productivity and resource availability. Non‐linear patterns and early signs of negative effects of late spring temperatures, however, suggest that productivity gains are likely to fade, if not turn negative in already warm regions, as warming intensifies.