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Recent declines of many European bird species have been linked with various environmental changes, especially land-use change and climate change. Since the intensity of these environmental changes varies among different countries, we can expect geographic variation in bird population trends. Here, we compared the population trends of bird species among neighbouring countries within central Europe (Czech Republic, Denmark, Germany, Switzerland) between 1990 and 2016 and examined trait-associations with population trends at both national and international scales. We found that Denmark had the highest proportion of declining species while Switzerland had the lowest. Species associated with farmland had negative trends, but the effect size tended to differ among countries. A preference for higher temperature was positively associated with population trends and its effect size was similar among countries. Species that were increasing across all four countries were associated with forest; while species that were decreasing across all countries were long-distance migrants or farmland birds. Our results suggest that land-use change tends to be a more regionally variable driver of common bird population trends than climate change in central Europe. For species declining across all countries, international action plans could provide a framework for more efficient conservation. However, farmland birds likely need both, coordinated international action (e.g. through a green agricultural policy) to tackle their widespread declines as well as regionally different approaches to address varying national effect trajectories. [ABSTRACT FROM AUTHOR]

Global climate change is driving species' distributions towards the poles and mountain tops during both non‐breeding and breeding seasons, leading to changes in the composition of natural communities. However, the degree of season differences in climate‐driven community shifts has not been thoroughly investigated at large spatial scales.We compared the rates of change in the community composition during both winter (non‐breeding season) and summer (breeding) and their relation to temperature changes.Based on continental‐scale data from Europe and North America, we examined changes in bird community composition using the community temperature index (CTI) approach and compared the changes with observed regional temperature changes during 1980–2016.CTI increased faster in winter than in summer. This seasonal discrepancy is probably because individuals are less site‐faithful in winter, and can more readily shift their wintering sites in response to weather in comparison to the breeding season. Regional long‐term changes in community composition were positively associated with regional temperature changes during both seasons, but the pattern was only significant during summer due to high annual variability in winter communities. Annual changes in community composition were positively associated with the annual temperature changes during both seasons.Our results were broadly consistent across continents, suggesting some climate‐driven restructuring in both European and North American avian communities. Because community composition has changed much faster during the winter than during the breeding season, it is important to increase our knowledge about climate‐driven impacts during the less‐studied non‐breeding season. [ABSTRACT FROM AUTHOR]